WO2009111540A1 - Methods for preparing pyridylethyl-substituted carbolines - Google Patents

Abstract

Methods of preparing pyridylethyl-substituted carbolines under reaction conditions that use fewer molar equivalents of MVP to produce the pyridylethyl-substituted carboline as compared to reported methods of preparing pyridylethyl-substituted carbolines using MVP are provided. Also provided are methods of preparing a pyridylethyl-substituted carboline using non-commercial MVP.

Description

METHODS FOR PREPARING PYRID YLETHYL-SUBSTITUTED CARBOLINES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority benefit of United States provisional patent application no. 61/033,759, filed March 4, 2008. The entire content of that application is hereby incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

[0002] Pyridy Ie thy 1- substituted carboline compounds have been suggested for use in the treatment of various disorders, such as Alzheimer's disease, neurodegenerative disorders, and schizophrenia (see, for example, U.S. Pat. No. 6,187,785 and U.S. Pat. Appl. Pub. No. 2007/0225316). Many syntheses of these compounds involve the use of methylvinylpyridine ("MVP"; 2-methyl-5-vinylpyridine). The existing synthetic routes using MVP tend to require about five to about ten molar equivalents, leading to increased cost of reagents and cost and impact of environmentally appropriate disposal. See, for example, U.S. Pat. No. 3,409,628 and U.S. Pat. No. 3,484,449.

[0003] The methods described herein address one or more of the existing drawbacks to using MVP in the synthesis of pyridy lethyl- substituted carbolines such as dimebon (2,8- dimethyl-5-[2-(6-methylpyridin-3-yl)ethyl]-3,4-dihydro-lH-pyrido[4,3-b]indole). Additionally, new solid forms of dimebon and methods of preparing those solid forms are disclosed.

BRIEF SUMMARY OF THE INVENTION

[0004] In one embodiment, the invention relates to new methods for the synthesis of pyridy lethyl- substituted carbolines using MVP. In one method, a pyridy lethyl- substituted carboline is prepared under reaction conditions that use fewer molar equivalents of MVP to produce the pyridy lethyl- substituted carboline as compared to reported methods of preparing pyridy lethyl- substituted carbolines using MVP. In another method, a pyridy lethyl- substituted carboline is prepared using non-commercial MVP, wherein the MVP is either generated in situ in the preparation of a pyridy lethyl- substituted carboline or is prepared just prior to use in the preparation of a pyridy lethyl- substituted carboline. In yet another method, a pyridylethyl- substituted carboline is prepared both (1) under reaction conditions that use fewer molar equivalents of MVP to produce the pyridylethyl- substituted carboline as compared to reported methods of preparing pyridylethyl- substituted carbolines using MVP, and (2) the MVP used is non-commercial MVP, wherein the MVP is either generated in situ in the preparation of a pyridylethyl- substituted carboline or is prepared just prior to use in the preparation of a pyridylethyl- substituted carboline. The methods detailed herein may be used in the preparation of various pyridylethyl- substituted carbolines and salts thereof and solvates of the foregoing. The invention specifically embraces methods of making dimebon (2,8- dimethyl-5-[2-(6-methylpyridin-3-yl)ethyl]-3,4-dihydro- lH-pyrido[4,3-b]indole) and salts thereof and solvates of all of the foregoing. In a particular variation, a method of preparing dimebon dihydrochloride dihydrate (dimebon • 2HCl • 2H₂O) is provided. [0005] In one embodiment, the invention relates to synthesis of, and alternate solid forms of, pyridylethyl- substituted carbolines and related compounds of the formula:

[0006] wherein Ri is Me, Et or PhCH₂ ; R₂ is H, PhCH₂ or 6-Me-3-Py-(CH₂)₂ ; and

R₃ is H, Me or Br, and salts, hydrates, or combined salt-hydrates. In particular, the invention relates to synthesis of, and alternate solid forms of, compounds where the compound is of formula I and:

[0007] (i) Ri = Et or PhCH₂, R₂ = R₃ = H,

[0008] (ii) Ri = R₃ = Me, R₂ = PhCH₂,

[0009] (iii) Ri = Me, R₂ = 6-Me-3-Py-(CH₂)₂, R₃ = H,

[0010] (iv) Ri = R₃ = Me, R₂ = 6-Me-3-Py-(CH₂)₂,

[0011] (v) Ri = Me, R₂ = H, R₃ = H or Me, or

[0012] (vi) Ri =Me, R₂ =H, R₃ =Br, and salts, hydrates, or combined salt-hydrates thereof with pharmacologically acceptable acids and quaternized derivatives. [0013] In another embodiment, the invention relates to synthesis of, and alternate solid forms of, the following pyridylethyl-substituted carbolines: 2,8-dimethyl-5-[2-(6- methyl-3-pyridyl)ethyl]-2,3,4,5-tetrahydro-lH-pyrido[ 4,3-b]indole; or 2-methyl-5-[2-(6- methyl-3-pyridyl)ethyl]-2,3,4,5-tetrahydro-lH-pyrido[4,3-b ]indole; or salts, hydrates, or combined salt-hydrates thereof.

[0014] In one embodiment, the invention embraces a method of making a pyridylethyl-substituted carboline and related compounds, comprising reacting a carboline compound of the formula:

[0015] where Ri and R₃ are as defined above for compound (I), or salts, hydrates, or combined salt-hydrates thereof, with a vinyl pyridine compound of the formula:

[0016] or a salt thereof, of in the presence of a base, to form the pyridylethyl- substituted carboline compound of the formula:

[0017] or salts, hydrates, or combined salt-hydrates thereof, in a yield of about 60% or greater. If the free base is formed, salts, hydrates, or combined salt-hydrates can be formed by further treatment as described herein. If the dihydrochloride dihydrate is formed, alternate salts, hydrates, or combined salt-hydrates can be formed by further treatment as described herein. The reaction above is of the form: base

Ii + in IV solvent where "base" and "solvent" are selected as described herein.

[0018] In one embodiment, the yield of pyridylethyl- substituted carboline compound

(IV) is about 60% or greater. In another embodiment, the yield of pyridylethyl-substituted carboline compound (IV) is about 65% or greater. In another embodiment, the yield of pyridylethyl-substituted carboline compound (IV) is about 70% or greater. In another embodiment, the yield of pyridylethyl-substituted carboline compound (IV) is about 75% or greater. In another embodiment, the yield of pyridylethyl-substituted carboline compound (IV) is about 80% or greater. In another embodiment, the yield of pyridylethyl-substituted carboline compound (IV) is about 85% or greater. In another embodiment, the yield of pyridylethyl-substituted carboline compound (IV) is about 90% or greater. In another embodiment, the yield of pyridylethyl-substituted carboline compound (IV) is about 95% or greater.

[0019] In one embodiment, the carboline (II) is selected from the group consisting of

2-methyl-2,3,4,5-tetrahydro-lH-pyrido[4,3-b]indole; 2,8-dimethyl-2,3,4,5-tetrahydro-lH- pyrido[4,3-b]indole; 2-methyl-8-bromo-2,3,4,5-tetrahydro- lH-pyrido[4,3-b]indole; 2-ethyl- 2,3,4,5-tetrahydro-lH-pyrido[4,3-b]indole; 2-benzyl-2,3,4,5-tetrahydro-lH-pyrido[4,3- b]indole; 2,8-dimethyl-5-benzyl-2,3,4,5-tetrahydrolH-pyrido[4,3-b]indole, or salts, hydrates, or combined salt-hydrates thereof.

[0020] In one embodiment, the carboline compound (II) is 2,8-dimethyl-2,3,4,5- tetrahydro-lH-pyrido[4,3-b]indole, or salts, hydrates, or combined salt-hydrates thereof. In another embodiment, the carboline compound (II) is 2,8-dimethyl-2,3,4,5-tetrahydro-lH- pyrido[4,3-b]indole, or salts, hydrates, or combined salt-hydrates thereof, and the pyridylethyl-substituted carboline compound (IV) is dimebon, or salts, hydrates, or combined salt-hydrates thereof.

[0021] In one embodiment, the carboline compound (II) is 2,8-dimethyl-

2,3,4,4a,5,9b-hexahydro-lH-pyrido[4,3-b]indole, or salts, hydrates, or combined salt- hydrates thereof.

[0022] In one embodiment, about 4 or less than about 4 equivalents of vinyl pyridine compound (III) per equivalent of carboline compound (II) are used for the reaction. In one embodiment, about 3 or less than about 3 equivalents of vinyl pyridine compound (III) per equivalent of carboline compound (II) are used for the reaction. In one embodiment, about 2 or less than about 2 equivalents of vinyl pyridine compound (III) per equivalent of carboline compound (II) are used for the reaction. In one embodiment, about 1.5 to about 2 equivalents of vinyl pyridine compound (III) per equivalent of carboline compound (II) are used for the reaction. In one embodiment, about 1.7 equivalents of vinyl pyridine compound (III) per equivalent of carboline compound (II) are used for the reaction.

[0023] The solvent for the reaction is selected from the group consisting of N-methyl pyrrolidone (NMP), dimethyl acetamide (DMAC), and diglyme (bis(2-methoxy ethyl ether). [0024] The reaction is carried out in the presence of a base, preferably a base having a potassium ion as cation; the base can be selected from the group consisting of KOH, K₃PO₄, tBuOK, tBuONa, tBuOLi, EtOK, EtONa, EtOLi, MeOK, and MeONa. In another embodiment, the base can be selected from the group consisting of KOH, K₃PO₄, tBuOK,

EtOK, and MeOK.

[0025] In one embodiment, the reaction of the carboline compound (II) with the vinyl pyridine compound (III) is carried out at a temperature of about 80 ⁰C to about 130 ⁰C. In another embodiment, the reaction of the carboline compound (II) with the vinyl pyridine compound (III) is carried out at a temperature of about 100 ⁰C to about 120 ⁰C. In one embodiment, the vinyl pyridine compound (III) is added as the last reagent, after the carboline compound (II) and base in the solvent have reached the desired reaction temperature.

[0026] In one embodiment, the reaction is performed for about 8 hours to about 26 hours. In another embodiment, the reaction is performed from about 16 hours to about 26 hours.

[0027] In one embodiment, the water content of the solvent is about 5 wt.% or less.

When K₃PO₄ is used as the base, the water content of the solvent is about 1 wt.% to about 5 wt.%. When tBuOK is used as the base, the water content of the solvent is about 1 wt.% or less.

[0028] In one embodiment, the solvents are degassed prior to use. In another embodiment, the solvents are degassed and then sparged with an inert gas, such as nitrogen or argon, prior to use. In another embodiment, the reaction vessels used are purged with inert gas, such as nitrogen or argon, prior to use. In another embodiment, the reaction is performed under an inert gas atmosphere, such as nitrogen or argon, for example, in a reaction vessel purged with inert gas such as nitrogen or argon prior to use.

[0029] In one embodiment where the carboline compound (II) is 2,8-dimethyl-

2,3,4,5,-tetrahydro-lH-pyrido[4,3-b]indole and the vinyl pyridine compound (III) is 2- methyl-5-vinylpyridine (MVP), about 1.5 equivalent MVP, about 1 equivalent 2,8-dimethyl-

2,3,4,5,-tetrahydro-lH-pyrido[4,3-b]indole free base and about 0.5 equivalent of tBuOK in

DMAC or diglyme are reacted at about 100⁰C - about 12O⁰C for about 8 hours.

[0030] In another embodiment where the carboline compound (II) is 2,8-dimethyl-

2,3,4,5,-tetrahydro-lH-pyrido[4,3-b]indole and the vinyl pyridine compound (III) is 2- methyl-5-vinylpyridine (MVP), about 1.5 equivalent MVP, about 1 equivalent 2,8-dimethyl-

2,3,4,5,-tetrahydro-lH-pyrido[4,3-b]indole HCl salt, and about 1.7 equivalent tBuOK in

DMAC or diglyme are reacted at about 100 ⁰C to about 120 ⁰C for about 8 hours. [0031] In another embodiment where the carboline compound (II) is 2,8-dimethyl-

2,3,4,5,-tetrahydro-lH-pyrido[4,3-b]indole and the vinyl pyridine compound (III) is 2- methyl-5-vinylpyridine (MVP), about 1.75 equivalent MVP, about 1 equivalent 2,8-dimethyl- 2,3,4,5,-tetrahydro-lH-pyrido[4,3-b]indole free base, and about 1.8 equivalent K₃PO₄ in DMAC are reacted at about 120 ⁰C for about 18 hours.

[0032] In another embodiment, the invention embraces a method of preparing a pyridylethyl- substituted carboline, comprising reacting a hydrazino compound of the formula:

[0033] or salts, hydrates, or combined salt-hydrates thereof, where R₃ is as defined above, with the compound:

[0034] to form an intermediate of the formula:

[0035] or salts, hydrates, or combined salt-hydrates thereof, and further reacting the intermediate with a 4-piperidinone compound of the form

[0036] where Ri is as defined above for formula (I), to form a pyridylethyl- substituted carboline compound of the formula:

or salts, hydrates, or combined salt-hydrates thereof. [0037] In general terms, the reactions above can be summarized as:

V + III ^► VI and base vi + vπ IV solvent where "base" and "solvent" are selected as described herein.

[0038] In one embodiment, about 4 or less than about 4 equivalents of vinyl pyridine compound (III) per equivalent of hydrazino compound (V) are used for the reaction. In one embodiment, about 3 or less than about 3 equivalents of vinyl pyridine compound (III) per equivalent of hydrazino compound (V) are used for the reaction. In one embodiment, about 2 or less than about 2 equivalents of vinyl pyridine compound (III) per equivalent of hydrazino compound (V) are used for the reaction. In one embodiment, about 1.5 to about 2 equivalents of vinyl pyridine compound (III) per equivalent of hydrazino compound (V) are used for the reaction.

[0039] In one embodiment, the hydrazino compound (V) is p-tolylhydrazine. In another embodiment, the 4-piperidinone compound is l-methyl-4-piperidinone (N-methyl-4- piperidinone). In another embodiment, the hydrazino compound (V) is p-tolylhydrazine, the 4-piperidinone compound (VII) is l-methyl-4-piperidinone (N-methyl-4-piperidinone), and the pyridylethyl-substituted carboline compound (IV) is dimebon, or salts, hydrates, or combined salt-hydrates thereof.

[0040] The solvent for the reactions is selected from the group consisting of N-methyl pyrrolidone (NMP), dimethyl acetamide (DMAC), and diglyme (bis(2-methoxy ethyl ether). [0041] The reaction of the hydrazino compound with the vinylpyridine compound is carried out in the presence of a base; the base is selected from the group consisting of KOH, K₃PO₄, tBuOK, tBuONa, tBuOLi, EtOK, EtONa, EtOLi, MeOK, and MeONa. In another embodiment, the base is selected from the group consisting of KOH, K₃PO₄, tBuOK, EtOK, and MeOK.

[0042] In another embodiment, when pyridylethyl-substituted carboline (IV) is prepared as the free base, it can be converted to the dihydrochloride dihydrate form by a method comprising: mixing dimebon free base with acetone; optionally heating the solution to about 3O⁰C to about 6O⁰C, about 4O⁰C to about 5O⁰C, or about 45⁰C; adding hydrochloric acid aqueous solution, optionally mixed with additional acetone (such as 37 wt% HCl mixed with acetone); and, if heated, cooling the solution to about O⁰C to about 25⁰C or about room temperature, or about 5⁰C to about 2O⁰C, or about 1O⁰C to about 15⁰C, and recovering the pyridylethyl-substituted carboline (IV) dihydrochloride dihydrate. In one embodiment, the pyridylethyl-substituted carboline (IV) is dimebon.

[0043] After completion of the reaction for preparation of the pyridylethyl-substituted carboline (IV), the product can be isolated by adding water and isolating the pyridylethyl- substituted carboline (IV) from the resultant slurry. In another embodiment, the product can be isolated by adding water and a small amount of water-immiscible solvent (for example, about 5% to about 25% of the volume of water added) to the reaction mixture, and isolating the pyridylethyl-substituted carboline (IV) from the resultant slurry. In another embodiment, the product can be isolated by adding water and a large amount of water-immiscible solvent (for example, about 25% to about 200% of the volume of water added) to the reaction mixture, where the pyridylethyl-substituted carboline (IV) is highly soluble in the water- immiscible solvent, followed by separating the water immiscible solvent from the aqueous layer and isolating the product by crystallization from the water-immiscible solvent; in this embodiment, the water can be extracted with additional portions (e.g., one, two, three, or more portions) of water-immiscible solvent, all portions of the water- immiscible solvent can be combined and optionally concentrated before isolating the product by crystallization. In another embodiment, the pyridylethyl- substituted carboline (IV) is further purified by recrystallization prior to use or conversion to a salt. In any of the foregoing embodiments, the pyridylethyl-substituted carboline (IV) can be dimebon.

[0044] Also described herein are various solid forms of dimebon dihydrochloride: anhydrous Form A, Form B hemi-hydrate, Form C monohydrate, Form D dihydrate, Form F trihydrate, and amorphous dimebon dihydrochloride.

[0045] In one embodiment, the invention embraces anhydrous dimebon dihydrochloride (Form A). This form is characterized by having carbon solid state NMR peaks at about 147.1, about 124.0, about 111.1, and about 21.6 ppm, referenced to an external sample of solid phase adamantane at 29.5 ppm. In another embodiment, the chemical shifts are within ± 0.2 ppm of the values indicated.

[0046] Form A can also be characterized by the following PXRD peaks having the indicated intensity at the specified angle: about 54.6% at about angle (°2-theta) 8.8; about 42.9% at about angle (°2-theta) 11.9; about 31.1% at about angle (°2-theta) 17.8; and about 100% at about angle (°2-theta) 24.9. In another embodiment, the values of intensities and angles can vary by + 5%.

[0047] In another embodiment, the invention comprises a method of making anhydrous dimebon dihydrochloride (Form A), comprising stirring or otherwise agitating dimebon dihydrochloride dihydrate in toluene for at least one day, e.g., 1 to 10 days, optionally evaporating the toluene and replacing with fresh toluene one, two, three, or more times, optionally at elevated temperature of about 30-120⁰C, about 80-100⁰C, or about 85- 95⁰C. The method can further comprise removal of the solvent and subjecting the resulting material to a vacuum of about 500 mbar or higher, about 300 mbar or higher, about 200 mbar or higher, about 100 mbar or higher, about 50 mbar or higher, or about 10 mbar or higher (where "higher vacuum" signifies a lower pressure, e.g., 50 mbar is a higher vacuum than 100 mbar).

[0048] In another embodiment, the invention embraces dimebon dihydrochloride hemi-hydrate (Form B). This form is characterized by having carbon solid state NMR peaks at about 148.5, about 133.8, about 117.0, and about 17.6 ppm, referenced to an external sample of solid phase adamantane at 29.5 ppm. In another embodiment, the chemical shifts are within ± 0.2 ppm of the values indicated. [0049] Form B can also be characterized by the following PXRD peaks having the indicated intensity at the specified angle: about 45.1% at about angle (°2-theta) 9.0; about

17.8% at about angle (°2-theta) 12.3; and about 100% at about angle (°2-theta) 25.2. In another embodiment, the values of intensities and angles can vary by ± 5%.

[0050] In another embodiment, the invention embraces a method of making dimebon dihydrochloride hemi-hydrate (Form B), comprising stirring or otherwise agitating dimebon dihydrochloride dihydrate in ethanol for at least about 5 days or about 5 to about 10 days, e.g., about 7 days, under ambient conditions, isolating the solid (e.g., by filtration such as centrifugal filtration), drying in a vacuum oven at a temperature between about 45-65⁰C, e.g., about 55⁰C, for at least about 30 minutes, e.g., approximately 30 to 90 minutes, or about 45 minutes.

[0051] In another embodiment, the invention embraces a method of making dimebon dihydrochloride hemi-hydrate (Form B), comprising stirring or otherwise agitating dimebon dihydrochloride dihydrate in acetonitrile for at least about 15 days or about 15 to about 30 days, e.g., about 23 days, under ambient conditions, isolating the solid (e.g., by filtration such as centrifugal filtration), drying in a vacuum oven at a temperature between about 45-65⁰C, e.g., about 55⁰C, for at least about 30 minutes, e.g., approximately 30 to 90 minutes or about

45 minutes.

[0052] In another embodiment, the invention embraces dimebon dihydrochloride monohydrate (Form C). This form is characterized by having carbon solid state NMR peaks at about 152.9, about 118.7, about 113.4, about 38.4, and about 30.2 ppm, referenced to an external sample of solid phase adamantane at 29.5 ppm. In another embodiment, the chemical shifts are within ± 0.2 ppm of the values indicated.

[0053] Form C can also be characterized by the following PXRD peaks having the indicated intensity at the specified angle: about 100% at about angle (°2-theta) 6.7; about

17.8% at about angle (°2-theta) 13.3; about 89.3% at about angle (°2-theta) 20.1; and about

41.8% at about angle (°2-theta) 24.5. In another embodiment, the values of intensities and angles can vary by ± 5%.

[0054] In another embodiment, the invention embraces a method of making dimebon dihydrochloride monohydrate (Form C), comprising stirring or otherwise agitating dimebon dihydrochloride in IPA under ambient conditions for at least about 8 days, or about 8 to about 20 days, such as 13 days, isolating the solid (e.g., by filtration) and drying in a vacuum dessicator for about 20 to 60 minutes, e.g., approximately 30 minutes.

[0055] Also described herein is dimebon dihydrochloride dihydrate (Form D). This form is characterized by having carbon solid state NMR peaks at about 149.9, about 132.9, about 22.5, and about 17.5ppm, referenced to an external sample of solid phase adamantane at 29.5 ppm. In another embodiment, the chemical shifts are within + 0.2 ppm of the values indicated.

[0056] Form D can also be characterized by the following PXRD peaks having the indicated intensity at the specified angle: about 100% at about angle (°2-theta) 8.6; about

12.5% at about angle (°2-theta) 12.9; about 14.6% at about angle (°2-theta) 13.5; and about

43.6% at about angle (°2-theta) 25.0. In another embodiment, the values of intensities and angles can vary by + 5%.

[0057] Also described herein is a method of making dimebon dihydrochloride dihydrate (Form D), comprising stirring or otherwise agitating dimebon free base in acetone, heating the solution to about 35⁰C to 6O⁰C, e.g. about 45⁰C, optionally filtering the solution, and adding HCl solution (e.g., 37 wt% HCl with about 0.25 volumes or more acetone, such as about 0.48 volumes). The addition can be done at elevated temperature of about 45⁰C to

85⁰C, e.g. at about 65⁰C. The material can then be cooled, for example to 10-15⁰C, and optionally filtered. The material can be dried at room temperature under vacuum with a nitrogen stream for about 3 hours to 12 hours, e.g., for about 6 hours.

[0058] In another embodiment, the invention embraces dimebon dihydrochloride trihydrate (Form F). This form is characterized by having carbon solid state NMR peaks at about 147.5, about 130.6, about 123.7, and about 44.7 ppm, referenced to an external sample of solid phase adamantane at 29.5 ppm. In another embodiment, the chemical shifts are within ± 0.2 ppm of the values indicated.

[0059] Form F can also be characterized by the following PXRD peaks having the indicated intensity at the specified angle: about 47.0% at about angle (°2-theta) 7.7; about

36.7% at about angle (°2-theta) 14.4; about 48.7% at about angle (°2-theta) 20.5; and about

100% at about angle (°2-theta) 26.0. In another embodiment, the values of intensities and angles can vary by ± 5%.

[0060] In another embodiment, the invention embraces a method of making dimebon dihydrochloride trihydrate (Form F), comprising adding methanol slowly (such as dropwise) to dimebon dihydrochloride dihydrate until the solid dissolves, and allowing the solution to evaporate. The solution can be optionally ground with a mortar during evaporation (in order to pulverize precipitating material).

[0061] In another embodiment, the invention embraces amorphous dimebon dihydrochloride. This form is characterized by having carbon solid state NMR peaks at about 151.5, about 125.0, about 111.3, and about 21.3 ppm, referenced to an external sample of solid phase adamantane at 29.5 ppm. In another embodiment, the chemical shifts are within ± 0.2 ppm of the values indicated.

[0062] In another embodiment, the invention embraces a method of making amorphous dimebon dihydrochloride, comprising dissolving dimebon dihydrochloride dihydrate in methanol, and evaporating the solvent at elevated temperature above about 35⁰C, such as between about 35⁰C and 75⁰C, or about approximately 55⁰C, which under a vacuum of about 500 mbar or higher, about 300 mbar or higher, about 200 mbar or higher, about 100 mbar or higher, about 50 mbar or higher, or about 10 mbar or higher (where "higher vacuum" signifies a lower pressure, e.g., 50 mbar is a higher vacuum than 100 mbar). [0063] The vacuum used for any of the above methods may be about 500 mbar or higher, about 300 mbar or higher, about 200 mbar or higher, about 100 mbar or higher, about 50 mbar or higher, or about 10 mbar or higher (where "higher vacuum" signifies a lower pressure, e.g., 50 mbar is a higher vacuum than 100 mbar).

[0064] The invention also embraces a composition comprising one or more of any of the anhydrous Form A, Form B hemi-hydrate, Form C monohydrate, Form F trihydrate, and amorphous dimebon dihydrochloride and a pharmaceutically acceptable carrier. The invention also embraces a composition comprising any individual solid form of dimebon and a pharmaceutically acceptable carrier. The invention also embraces a composition comprising a mixture of two or more solid forms of anhydrous Form A, Form B hemi- hydrate, Form C monohydrate, Form D dihydrate, Form F trihydrate, and amorphous dimebon dihydrochloride in any proportion. The invention also embraces a composition comprising a mixture of two or more solid forms of dimebon in any proportion, additionally comprising a pharmaceutically acceptable carrier.

[0065] For all novel compounds and/or compositions, the compound and/or composition can comprise the compound and/or composition indicated, consist essentially of the compound and/or composition indicated, or consist of the compound and/or composition indicated. For all novel methods, the method can comprise the method steps indicated, consist essentially of the method steps indicated, or consist of the method steps indicated.

BRIEF DESCRIPTION OF THE FIGURES

[0066] Figure 1 depicts, from bottom to top, a comparison of the proton decoupled

¹³C CPMAS spectra of dimebon dihydrochloride: A. anhydrous Form A; B. Form B hemi- hydrate; C. Form C monohydrate; D. Form D dihydrate; F. Form F trihydrate; and E. amorphous. ¹³C CPMAS spectra were taken at 1O⁰C, with sealed cap, spinning at 15.0 kHZ, referenced to adamantane at 29.5 ppm.

[0067] Figure 2 depicts, from bottom to top, a comparison of the 0-70 ppm region of the proton decoupled ¹³C CPMAS spectra of dimebon dihydrochloride: A. anhydrous Form A; B. Form B hemi-hydrate; C. Form C monohydrate; D. Form D dihydrate; F. Form F trihydrate; and E. amorphous. Peaks included in the unique peak set for each form are noted with arrows. ¹³C CPMAS spectra were taken at 1O⁰C, with sealed cap, spinning at 15.0 kHZ, referenced to adamantane at 29.5 ppm.

[0068] Figure 3 depicts, from bottom to top, a comparison of the 90-160 ppm region of the proton decoupled ¹³C CPMAS spectra of dimebon dihydrochloride A. anhydrous Form A; B. Form B hemi-hydrate; C. Form C monohydrate; D. Form D dihydrate; F. Form F trihydrate; and E. amorphous. Peaks included in the unique peak set for each form are noted with arrows. ¹³C CPMAS spectra were taken at 1O⁰C, with sealed cap, spinning at 15.0 kHZ, referenced to adamantane at 29.5 ppm.

[0069] Figure 4 depicts the powder x-ray diffraction pattern of dimebon dihydrochloride anhydrous Form A.

[0070] Figure 5 depicts the ssNMR carbon spectrum of dimebon dihydrochloride anhydrous Form A.

[0071] Figure 6 depicts the powder x-ray diffraction pattern of dimebon dihydrochloride Form B hemi-hydrate.

[0072] Figure 7 depicts the ssNMR carbon spectrum of dimebon dihydrochloride

Form B hemi-hydrate. The peaks marked by asterisks are spinning sidebands. [0073] Figure 8 depicts the powder x-ray diffraction pattern of dimebon dihydrochloride Form C monohydrate. [0074] Figure 9 depicts the ssNMR carbon spectrum of dimebon dihydrochloride

Form C monohydrate. The peaks marked by asterisks are spinning sidebands.

[0075] Figure 10 depicts the powder x-ray diffraction pattern of dimebon dihydrochloride Form D dihydrate

[0076] Figure 11 depicts the ssNMR carbon spectrum of dimebon dihydrochloride

Form D dihydrate. The peaks marked by asterisks are spinning sidebands.

[0077] Figure 12 depicts the powder x-ray diffraction pattern of amorphous dimebon dihydrochloride.

[0078] Figure 13 depicts the ssNMR carbon spectrum of amorphous dimebon dihydrochloride. The peaks marked by asterisks are spinning sidebands.

[0079] Figure 14 depicts the powder x-ray diffraction pattern of dimebon dihydrochloride Form F trihydrate

[0080] Figure 15 depicts the ssNMR carbon spectrum of dimebon dihydrochloride

Form F trihydrate. The peaks marked by asterisks are spinning sidebands.

DETAILED DESCRIPTION OF THE INVENTION

[0081] Improved methods of making pyridylethyl- substituted carbolines using noncommercial MVP are provided, which use lower equivalent amounts of MVP, base, or both MVP and base, as compared to previously reported methods of making pyridylethyl- substituted carbolines. The MVP used can be commercially prepared MVP, MVP generated in situ in the preparation of a pyridylethyl- substituted carboline or MVP prepared just prior to use in the preparation of a pyridylethyl- substituted carboline. Non-commercial MVP refers to MVP that is not obtained directly from a commercial source and is not purified from commercially available MVP. Non-commercial MVP may be produced in situ from an MVP precursor or can be prepared just prior to use from an MVP precursor by a variety of methods, such as but not limited to those shown in Scheme 1 below.

6

One of X and Y = halo or pseudohalo group (e.g., a triflate); the X or Y that is not a halo or pseudohalo group is a metal such as tributyltin or boric acid.

Scheme 1. Preparation of non-commercial MVP.

[0082] In reaction (I) of Scheme 1, an MVP precursor, 5-(l-chloroethyl)-2- methylpyridine (3), is prepared from l-(6-methylpyridin-3-yl)ethanol (1) in any form (e.g., can be a salt form such as by addition of maleic acid (2)), under appropriate reaction conditions and can generate MVP under appropriate reaction conditions, such as in the presence of KOH or NaOH and a THF or NMP solvent. In reaction (II) of Scheme 1, dehydration of an MVP precursor, l-(6-methylpyridin-3-yl)ethanol (1) or 2-(6- methylpyridin-3-yl)ethanol (5), under appropriate reaction conditions provides MVP (4) (2- methyl-5-vinylpyridine, 5-ethenyl-2-methyl-pyridine, or 5-vinyl-2-picoline). In reaction (III) of Scheme 1, e.g., 5-halo-2-methylpyridine or a like compound is coupled under appropriate reaction conditions to an appropriately substituted vinyl group to provide MVP (4). Other methods for production are possible. In any of the described processes, an MVP precursor may be converted to MVP in a batch-wise or continuous process and the resultant product mixture may be reacted directly with a carboline to provide a pyridylethyl- substituted carboline. If desired, purification or removal of impurities from the reaction product mixture may be conducted. However, MVP can be used without isolation and storage beyond typical processing times.

Scheme IA. Alternate preparation of compound (5)

[0083] Compound (5) can also be prepared by the route outlined in Scheme IA.

[0084] MVP that is prepared in the presence of a carboline or carboline precursor is prepared in situ. For instance, if an MVP precursor and a carboline or carboline precursor are in the same reaction vessel and MVP is generated from the MVP precursor and is available for reaction with the carboline or carboline precursor in the same reaction vessel, the MVP is deemed generated in situ. However, if MVP is prepared from an MVP precursor not in the presence of a carboline or carboline precursor, such as when MVP is prepared in one reaction vessel and is then added to a different reaction vessel for reaction with a carboline or carboline precursor or a carboline or carboline precursor is added to the reaction vessel containing the MVP so produced, the MVP is said to be prepared just prior to use. The advantage of in situ generation of MVP or preparation of MVP just prior to use is that it avoids storage and shipping of large quantities of MVP, which must be stored with stabilizers to avoid hazardous polymerization reactions, and which has a relatively short shelf-life. [0085] Commercially available MVP, MVP prepared in situ, or MVP prepared just prior to use may be reacted with a carboline, such as a tetrahydro-gamma-carboline, to provide a pyridylethyl- substituted carboline. Carbolines and carboline precursors may be obtained commercially or prepared according to existing synthetic methods or those detailed herein. A particular carboline used in the preparation of dimebon and salts and solvates thereof is 2,8-dimethyl-2,3,4,5,-tetrahydro-lH-pyrido[4,3-b]indole shown in Scheme 2 below as compound (8). In this reaction, the carboline (8) is prepared by reaction of p- tolylhydrazine with l-methyl-4-piperidone. Alternative methods may also be used.

8

Scheme 2. Preparation of 2,8-dimethyl-2,3,4,5-tetrahydro-lH-pyrido[4,3-b]indole (8).

[0086] Preparations of pyridylethyl- substituted carbolines are exemplified by the preparation of dimebon. Alkylation of carboline (8) with MVP obtained commercially, generated in situ, or generated just prior to use provides dimebon as a free base (treatment of a free base of dimebon with HCl in acetone provides dimebon dihydrochloride in the dihydrate form; see Example 7 below). Carboline»HCl can be converted to the free base for reaction with MVP, or additional base can be added to the reaction mixture to avoid the additional step of converting the carboline to the free base.

[0087] Regardless of the genesis of MVP, there is a need for a process with increased efficiency to produce pyridylethyl- substituted carbolines, such as dimebon, from MVP and carboline. For instance, the currently used process for the preparation of dimebon uses 5 - 10 equivalents of MVP. This is a large amount of MVP from a cost perspective as well as for storage, handling and disposal. The process also involves several distillations of MVP and MVP/solvent mixtures to drive the reaction to completion, providing about 71% of dimebon free base.

[0088] Improved methods of making pyridylethyl- substituted carbolines under reaction conditions that use fewer molar equivalents of MVP to produce the pyridylethyl- substituted carboline as compared to reported methods of preparing pyridylethyl-substituted carbolines using MVP are provided by this invention. The improved process preferably achieves a similar yield to that reported in the literature, but uses fewer equivalents of MVP, preferably about 4 equivalents of MVP or fewer than 4 equivalents of MVP, more preferably about 3 equivalents of MVP or fewer than about 3 equivalents of MVP, still more preferably about 2 equivalents of MVP or fewer than about 2 equivalents of MVP. The improved processes of this invention are characterized primarily by careful matching of solvent and base for the addition of vinylpyridines to carbolines. The new methods of synthesis detailed herein use lower amounts of base, such as 1.3 to 2, 1.5 to 2, or 1.5 to 3 equivalents of bases such as KOH and K₃PO₄ while also reducing the number of equivalents of MVP needed for the reaction. This process works with MVP, including MVP obtained from commercial sources, or with non-commercial MVP, such as MVP that has been prepared just prior to use. [0089] Examples of compatible solvents, bases, and temperatures, and the resulting reduced amount of MVP required for reaction, are given in the following table.

Solvent Bases Temp MVP Equivalents

DMAC NaOMe, t-BuOK, Na-t- 100-130 ⁰C 1.05 - - 2.0 amylate

Diglyme NaOMe, t-BuOK, Na-t- 100-130 ⁰C 1.5 - 2.0 amylate, KOH, NaOH

NMP NaOMe, t-BuOK, Na-t- 100-130 ⁰C 1.05 - - 2.0 amylate

[0090] The invention also encompasses salts of the compounds generated by the methods detailed herein. For example, the invention embraces a method of preparing dimebon or a salt thereof, including but not limited to the dimebon dihydrochloride salt. Other salts are also embraced by the invention, such as a monophosphate salt of dimebon. [0091] Solvates, in particular hydrates, of the compounds and salts thereof are also embraced. For example, the invention embraces a method of preparing dimebon, a dimebon salt or a solvate of the foregoing, such as the monohydrate, dihydrate or trihydrate. In a particular variation, a method of preparing the dihydrate of dimebon dihydrochloride is provided. Dimebon dihydrochloride dihydrate is thus embraced by this invention, as are methods of making and using it.

[0092] Also described are dosage forms of compounds prepared by the methods detailed herein. All available dosage forms are contemplated, including unit dosage forms prepared with a therapeutically effective amount of compound. As used herein, "unit dosage form" refers to physically discrete units, suitable as unit dosages, each unit containing a predetermined quantity of active ingredient calculated to produce the desired therapeutic effect in association with the required pharmaceutical carrier. Unit dosage forms may contain a single or a combination therapy. [0093] The dosages can be formulated as controlled release formulations.

"Controlled release" refers to a drug-containing formulation or fraction thereof in which release of the drug is not immediate, i.e., with a "controlled release" formulation, administration does not result in immediate release of the drug into an absorption pool. The term encompasses depot formulations designed to gradually release the drug compound over an extended period of time. Controlled release formulations can include a wide variety of drug delivery systems, generally involving mixing the drug compound with carriers, polymers or other compounds having the desired release characteristics (e.g., pH-dependent or non-pH-dependent solubility, different degrees of water solubility, and the like) and formulating the mixture according to the desired route of delivery (e.g., coated capsules, implantable reservoirs, injectable solutions containing biodegradable capsules, and the like). [0094] Any of the compounds disclosed herein, or combinations thereof, can also be combined with a pharmaceutically acceptable carrier, pharmaceutically acceptable excipient, pharmacologically acceptable carrier or pharmacologically acceptable excipient. By "pharmaceutically acceptable carrier," "pharmaceutically acceptable excipient," "pharmacologically acceptable carrier" or "pharmacologically acceptable excipient" is meant a material that is not biologically or otherwise undesirable, e.g., the material may be incorporated into a pharmaceutical composition administered to a patient without causing any significant undesirable biological effects or interacting in a deleterious manner with any of the other components of the composition in which it is contained. Pharmaceutically acceptable carriers or excipients have preferably met the required standards of toxicological and manufacturing testing and/or are included on the Inactive Ingredient Guide prepared by the U.S. Food and Drug administration.

[0095] Any of the compounds disclosed herein, or combinations thereof, can also be formulated as a pharmaceutically acceptable salt or salts. "Pharmaceutically acceptable salts" are those salts which retain at least some of the biological activity of the free (non-salt) compound and which can be administered as drugs or pharmaceuticals to an individual. A pharmaceutically acceptable salt intends ionic interactions and not a covalent bond. As such, an N-oxide is not considered a salt. Such salts, for example, include: (1) acid addition salts, formed with inorganic acids such as hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, phosphoric acid, and the like; or formed with organic acids such as acetic acid, oxalic acid, propionic acid, succinic acid, maleic acid, tartaric acid and the like; (2) salts formed when an acidic proton present in the parent compound either is replaced by a metal ion, e.g., an alkali metal ion, an alkaline earth ion, or an aluminum ion; or coordinates with an organic base. Acceptable organic bases include ethanolamine, diethanolamine, triethanolamine and the like. Acceptable inorganic bases include aluminum hydroxide, calcium hydroxide, potassium hydroxide, sodium carbonate, sodium hydroxide, and the like. Further examples of pharmaceutically acceptable salts include those listed in Berge et al, Pharmaceutical Salts, J. Pharm. ScL 1977 Jan;66(l):l-19. Pharmaceutically acceptable salts can be prepared in situ in the manufacturing process, or by separately reacting a purified compound of the invention in its free acid or base form with a suitable organic or inorganic base or acid, respectively, and isolating the salt thus formed during subsequent purification. It should be understood that a reference to a pharmaceutically acceptable salt includes the solvent addition forms or crystal forms thereof, particularly solvates or polymorphs. Solvates contain either stoichiometric or non- stoichiometric amounts of a solvent, and are often formed during the process of crystallization. Hydrates are formed when the solvent is water, or alcoholates are formed when the solvent is alcohol. Polymorphs include the different crystal packing arrangements of the same elemental composition of a compound. Polymorphs usually have different X-ray diffraction patterns, infrared spectra, melting points, density, hardness, crystal shape, optical and electrical properties, stability, and solubility. Various factors such as the recrystallization solvent, rate of crystallization, and storage temperature may cause a single crystal form to dominate.

[0096] The term "carrier" or "excipient" as used herein means an inert or inactive substance that may be used in the production of a drug or pharmaceutical, such as a tablet containing a compound of the invention as an active ingredient. Various substances may be embraced by the terms carrier or excipient, including without limitation any substance used as a binder, disintegrant, coating, compression/encapsulation aid, cream or lotion, lubricant, solutions for parenteral administration, materials for chewable tablets, sweetener or flavoring, suspending/gelling agent, or wet granulation agent. Binders include, e.g., carbomers, povidone, xanthan gum, etc.; coatings include, e.g., cellulose acetate phthalate, ethylcellulose, gellan gum, maltodextrin, enteric coatings, etc.; compression/encapsulation aids include, e.g., calcium carbonate, dextrose, fructose dc (dc = "directly compressible"), honey dc, lactose (anhydrate or monohydrate; optionally in combination with aspartame, cellulose, or microcrystalline cellulose), starch dc, sucrose, etc.; disintegrants include, e.g., croscarmellose sodium, gellan gum, sodium starch glycolate, etc.; creams or lotions include, e.g., maltodextrin, carrageenans, etc.; lubricants include, e.g., magnesium stearate, stearic acid, sodium stearyl fumarate, etc.; materials for chewable tablets include, e.g., dextrose, fructose dc, lactose (monohydrate, optionally in combination with aspartame or cellulose), etc.; suspending/gelling agents include, e.g., carrageenan, sodium starch glycolate, xanthan gum, etc.; sweeteners include, e.g., aspartame, dextrose, fructose dc, sorbitol, sucrose dc, etc.; and wet granulation agents include, e.g., calcium carbonate, maltodextrin, microcrystalline cellulose, etc.

[0097] Compounds prepared by the methods detailed herein may find use in the treatment and/or prevention of a neurodegenerative or other disease or may find use as an antihistamine. For instance, dimebon and salts thereof and hydrates of the foregoing prepared by the methods detailed herein may be used in the treatment and/or prevention of Alzheimer's disease, Huntington's disease, canine cognitive dysfunction syndrome, ALS, schizophrenia, ischemia/reperfusion injury of the brain, mild cognitive impairment and in methods of slowing aging in a mammal or methods of slowing the aging of a cell, tissue, or organ. They may be administered alone or in combination with other active agents. [0098] The examples provided below illustrate but are not intended to limit the invention. Various modifications to the experimental conditions reported below may be made. For example, the reactions may proceed with different reactant ratios, solvents, temperature, etc. In addition, the invention embraces modifications to the reaction conditions that accompany scale-up to production quantities of drug.

EXAMPLES Example 1. Preparation of l-(6-methylpyridin-3-yl)ethanol (1)

[0099] WBu₃MgLi was prepared by treating ^Bu₂Mg (1 equiv.) in THF (2 vol.) with wBuLi (0.5 equiv.) at 0 ⁰C. 3-bromopicoline in THF (2 vol.) was then added, maintaining temperature between -10 and 0 ⁰C, and allowed to stir for 30 minutes forming the "ate" complex. Acetaldehyde (5 or preferably 3 equiv.) in THF (2 vol.) was added to the "ate" complex and the reaction was complete within one hour. The reaction was quenched with a base such as 2N NaOH and partially concentrated under reduced pressure. 1-Pyridylethanol in any suitable form, such as but not limited to a salt such maleic acid salt, was extracted with isopropyl acetate (IPAC) and azeotropically dried prior to the addition of maleic acid in methanol. The solution was heated to 40 ⁰C for 1 hour and diluted with IPAC. Upon cooling to 5-10 ⁰C, the maleate salt was filtered and washed with IPAC to give the maleate salt in 55% yield and in high purity by ¹H-NMR. The active magnesate species may be further modified by using wBuMgCl (1 equiv) and MeLi (2 equiv) to give «BuMe2MgLi, which increased yield to 80-85% and gave a colorless maleate salt.

Example 2. Preparation of MVP from l-(6-methylpyridin-3-yl)ethanol (1)

[00100] Maleate salt in IPAC (10 vol.) was treated with 2N NaOH and separated. The

IPAC solution was concentrated under reduced pressure, azeotropically removing water, and re-diluted to 2.5 volumes. The 1-pyridylethanol solution was slowly added to a mixture of SOCl₂ (1.5 equiv) in IPAC (2.5 vol.). Upon completion, the reaction was diluted with 2N NaOH, phases separated, and the chloride in IPAC is solvent swapped into NMP (4.2 vol.) and 3.5 equiv. of KOH was added. After 4 hrs. at 50 ⁰C, the elimination to MVP was complete. MVP was obtained in high yield and purity by ¹H-NMR. Reaction completion for the MVP formation is preferably driven to >99% to avoid reaction by-product in subsequent steps via reaction of the intermediate chloride with a carboline, which by-products can be purged via crystallization. Example 3. Preparation of 2,8-dimethyl-2,3,4,5-tetrahydro-lH-pyrido[4,3-b]indole hydrochloride (8)

[00101] Addition of l-methyl-4-piperidone to a stirred solution of p-tolylhydrazine in

IPA (20 vol.) at 40 ⁰C provided the hydrazone intermediate within 1 hour. The solution was treated with HCl and the Carboline«HCl (8) precipitates. Upon cooling to room temperature, the salt was filtered and washed with IPA/MTBE. Carboline»HCl (8) was obtained in good yield with > 99% AUC purity.

Example 4. Preparation of dimebon from MVP and carboline (8)

[00102] To MVP (2 equiv) and KOH (7 equiv.) in NMP (5 vol.) was added carboline free base (8) and the reaction was heated to 100 ⁰C. After 24-48 hrs, 75-80% conversion was obtained and the reaction was cooled to RT and diluted with water (5 vol.) and IPAC (5 vol.). Phases were separated and the aqueous portion was re-extracted with IPAC (2X 5 vol.). The combined organics were washed with water (3 X 5 vol.) to remove NMP and were concentrated under reduced pressure to a minimum, azeotropically removing water, and re- diluted to 5 volumes with MTBE. After stirring at RT, dimebon crystallized and was filtered. Dimebon was obtained in ca. 55% yield (200 mg scale) and in high purity by HPLC (>98.5% AUC).

Example 5. Large-scale Preparation of 2,8-dimethyl-2,3,4,5-tetrahydro-lH-pyrido[4,3- b]indole free base (10)

[00103] Water (26.25 kg) was charged to a 50 L reaction vessel followed by p- tolylhydrazine hydrochloride (1.75 kg). Dissolution occurred after 15 minutes of stirring at room temperature and N-methyl-4-piperidone (1.56 kg) was added over a period of four minutes. The batch was then heated to a range of 45-55 ⁰C and cone. HCl was added (3.97 kg) over 50 minutes. The solution was held overnight (17 hours) before a sample was taken, at which point the HPLC IPC indicated 0.07% AUC /?-tolylhydrazine remaining. The reaction was cooled to 30-45 ⁰C and addition of -4.5 L of 6.25N NaOH brought the solution to pH 3.2. Slight precipitation that occurred at this pH did not re-dissolve after the addition was discontinued. MTBE (1.94 kg) was added and precipitation was continued by further addition of ~4 L of 6.25 N NaOH to bring the final pH to 12.4. The slurry was allowed to stir for 30 minutes at 30-45 ⁰C and then was cooled over 1.5 hours to a range of 5-15 ⁰C. The batch was held for 30 minutes followed by a fast filtration through a table-top filter (sharkskin, 14 minutes). The cake was washed with water (8.75 kg) and cold MTBE (3.89 kg) and then conditioned on the filter for one hour before transferring to drying trays. The batch was dried under reduced pressure at 70 ⁰C for 68 hours to reduce the water level to <1.0%. 1.99 kg of carboline free base (10) was isolated in 90% yield. Example 6. Preparation of dimebon from MVP and carboline (10)

[00104] Carboline free base (10) and K₃PO₄ (5 mol equiv, 2.6 wt. equiv) were charged to a reactor and purged with nitrogen. Then, DMAC (5 vol, 3.749 wt. equiv) followed by MVP (1.75 mol. equiv, 1.04 wt. equiv) were added and the resulting slurry was stirred at 100⁰C for 24h. The temperature was then adjusted to 40-60⁰C and water (23.5 vol, 23.5 wt. equiv) was slowly added over Ih. The mixture was cooled to RT and stirred for 2 hours. The slurry was filtered off and the resulting solid was washed with water (5 vol, 5 wt. equiv), dried in the oven at 5O⁰C under vacuum for 16h. Dimebon free base is obtained in 80% isolated yield.

Example 7. Preparation of dimebon dihydrochloride dihydrate from dimebon free base

[00105] Dimebon free base and acetone (8.44 vol, 6.67 equiv) were charged to a reactor inerted with nitrogen and the resulting solution was heated to 45⁰C. The solution was polish-filtered through a lμ in-line filter and the filter washed with acetone (1.2 vol, 0.95 equiv). Dilute 37 wt% HCl (2.35 mol equiv, 0.607 vol) with acetone (0.48 vol) was slowly added over 40 min (temperature raised to 65⁰C). The resulting slurry was cooled to 10-15⁰C and filtered. The cake was washed with acetone (4.82 vol) then dried at RT under vacuum with a nitrogen stream for 6h. Dimebon 2HC1, 2H₂O is obtained in 84% isolated yield.

Example 8. Various coupling conditions for carboline and methylvinylpyridine [00106] The coupling reaction of carboline with methylvinylpyridine was run under various conditions of solvent and temperature, using different bases and equivalents of MVP as indicated in the following table.

Solvent Bases Temp MVP Equivalents

DMAC NaOMe, t-BuOK, Na-t- 100-130 ⁰C 1.05 - - 2.0 amylate

Diglyme NaOMe, t-BuOK, Na-t- 100-130 ⁰C 1.5 - 2.0 amylate, KOH, NaOH

NMP NaOMe, t-BuOK, Na-t- 100-130 ⁰C 1.05 - - 2.0 amylate

[00107] Reactions were run with both carboline hydrochloride and the free base of the carboline. If the hydrochloride was used 1.5 equivalents of base was used, if the free base was used, 0.5 equivalents of base was used.

[00108] An exemplary procedure with dimethyl acetamide solvent and potassium t- butoxide base follows: to a three neck 125 ml round bottom flask was added 42 ml of DMAC. Rapid stirring was begun and carboline HCl (14 g, 54.6 mmol) was added. Potassium t-butoxide (10.8 g, 91.8 mmol) was added and the mixture was heated to 120⁰C. 2-methyl-5-vinylpyridine was added in 5 portions over a 30 min period (10.82 g, 82 mmol). After 4-5 hr, 0.13 ml of water was added in two portions to accelerate the reaction. After 21 hr the reaction was cooled to 5O⁰C and 50 ml of water was charged to the reaction vessel. The reaction mixture was then cooled to 3O⁰C. The mixture was seeded with 200 mg of dimebon free base. Another 34 mL of water was added over a 90 min period. The slurry was cooled to 22⁰C over a 10 min period, then to 2⁰C over a 30 min period. The slurry was filtered and washed with 70 mL water in 3 portions. After vacuum drying at 5O⁰C with N₂ sweep, 8.48 grams tan solid was obtained (49% yield). [00109] An exemplary procedure with diglyme solvent and potassium hydroxide base follows:

[00110] Carboline free base (9.5 g, leq.) was dissolved in diglyme (47mL) then MVP

(9mL, 1.44eq.) and ground KOH flakes (5.3g, 1.8 eq.) were added and the heterogeneous mixture was heated to 120⁰C for 42 hr. HPLC shows 99% conversion to Dimebon free base. The reaction was cooled to 5O⁰C, diluted with water (75 mL), then seeded (5 mg) and cooled further to 5°C to crystallize. The product was isolated by filtration, washed with water (7OmL) and dried under vacuum with nitrogen stream to afford dimebon free base (7.2g) in 52% yield.

Example 9. Alternate synthetic route proceeding via tolylhydrazine

[00111] p-Tolylhydrazine free-base (3.5 g) was stirred in DMAC (9.7 vol) with MVP

(2 equiv) and K₃PO₄ (5.7 equiv) at 100 ⁰C. The reaction was followed by HPLC and clean conversion was observed to one product. After 22 hrs, the reaction was diluted with water to dissolve the phosphate and separated. The bi-phasic toluene/DMAC layers were then separated and the DMAC was back-extracted with toluene. The combined organics were washed with water to remove residual DMAC and concentrated to an oil. Upon addition of heptane, solids crystallized and were isolated by filtration to afford 3.16 g of the hydrazine analog Int-1.

[00112] Hydrazine analog Int-1 (73 mg) was stirred in IPA (20 volumes) and N-

Methyl-4-Piperidone (1 equiv) was added. Cone. HCl (3 equiv) was added and the reaction was gently warmed where a fine precipitate formed. After stirring 15 minutes, additional cone. HCl (3 equivalents) was added and an oil was obtained. The reaction mixture was neutralized with 2N NaOH and the product was extracted with toluene and concentrated to an oil. After the addition of MTBE, the white precipitate was isolated by filtration to provide 39 mg of Dimebon free base. Example 10: Preparation, powder x-ray diffraction analysis, and solid-state NMR analysis of various forms of dimebon

[00113] Various solid forms of dimebon dihydrochloride were prepared using the procedures described herein. Powder x-ray diffraction patterns of the various forms were obtained. Solid state nuclear magnetic resonance spectra of the various forms of dimebon were also obtained. Bruker TopSpin 2.0 software was used to visualize and evaluate ssNMR spectra. Specific instrument methods for each form are provided below. The following peak picking parameters were used to make preliminary peak assignments: intensity of reference peak set to 12, minimum intensity of 1, maximum intensity of 1000, detection sensitivity of 0.2, and fraction of peak height for width calculation set to 0.5. The output of automated assignments was visually checked to ensure validity and adjustments manually made if necessary. Additionally, peaks were manually assigned within spectra if appropriate. [00114] Table 1 below compares carbon chemical shifts (ppm, referenced to external sample of solid phase adamantane at 29.5 ppm) observed for Dimebon Dihydrochloride anhydrous Form A, Form B hemi-hydrate, Form C monohydrate, Form D dihydrate, Form F trihydrate, and amorphous. Characteristic sets of peaks for each form which can be used to distinguish each form from the remaining forms are listed in bold italics. An asterisk (*) next to a chemical shift indicates a peak shoulder.

Table 1

[00115] Table 2 below lists sets of carbon chemical shifts (ppm, referenced to external sample of solid phase adamantane at 29.5 ppm) to uniquely (± 0.2 ppm) define dimebon dihydrochloride anhydrous Form A, Form B hemi-hydrate, Form C monohydrate, Form D dihydrate, Form F trihydrate, and amorphous.

Table 2

Example 1OA: Preparation, powder x-ray diffraction, and ssNMR of anhydrous

Dimebon Dihydrochloride Form A

[00116] 800 mg of dimebon dihydrochloride dihydrate was placed in a IL round bottomed flask. Approximately 500 mL toluene was added. Solution was evaporated at approximately 85-95 ⁰C under reduced pressure (300-500 mbar) until volume was reduced to approximately 200 mL. Toluene addition and evaporation was repeated twice. Yellowish solid was observed in solution. Solution was placed in a glass flask. Solution was placed in a dessicator with dessicant and house vacuum was pulled for 10 days. Solid was collected using vacuum filtration in a 60 mL, 40M Kimax sintered glass funnel. Solid was placed in a vacuum dessicator overnight. Material was analyzed by PXRD to confirm solid form; see Table 3 and Table 4 below, and Figure 4.

[00117] Solid-state NMR Instrument Method: Approximately 80 mg of sample were tightly packed into a 4 mm ZrO₂ rotor. A rotor cap fitted with O-rings was used to seal the rotor. Spectra were collected at ambient pressure on a Bruker-Biospin 4 mm BL HFX CPMAS probe positioned into a wide -bore Bruker-Biospin Avance DSX 500 MHz (¹H frequency) NMR spectrometer. The sample was cooled with a direct stream of nitrogen onto the rotor having an output temperature of 10°C at a flow rate of 1200 liters/hour. The packed rotor was oriented at the magic angle and spun at 15.0 kHz. The ¹³C solid state spectrum was collected using a proton decoupled cross-polarization magic angle spinning experiment (CPMAS). The cross-polarization contact time was set to 2.0 ms. A proton decoupling field of approximately 85 kHz was applied. 28,672 scans were collected with recycle delay of 3.25 seconds. The carbon spectrum (Figure 5) was referenced using an external standard of crystalline adamantane, setting its upfield resonance to 29.5 ppm; see Table 5 below.

Table 3. Form A PXRD Peaks

Table 4. Form A Unique PXRD Peaks

Table 5. Carbon chemical shifts observed for anhydrous dimebon dihydrochloride Form A

(a) Referenced to external sample of solid phase adamantane at 29.5 ppm.

(b) Defined as peak heights. Intensities can vary depending on the actual setup of the CPMAS experimental parameters and the thermal history of the sample. CPMAS intensities are not necessarily quantitative.

*Peak shoulder

Example 1OB: Preparation, powder x-ray diffraction, and ssNMR for Dimebon

Dihydrochloride Form B hemi-hydrate

[00118] Method 1 - Approximately 60 mg of dimebon dihydrochloride dihydrate was placed in a 4 mL glass scintillation vial. 2 mL of ethanol was added and solution was capped and stirred. All solid dissolved therefore more solid was added until solution was saturated. Solution was capped and stirred for 7 days under ambient conditions. Solid was recovered from solution using centrifugal filtration in microcentrifuge tubes equipped with 0.45 μm nylon filter membrane inserts. Filtrand was dried in a 55 ⁰C vacuum oven for approximately 45 minutes. Solid was analyzed using PXRD and was form B. Filtrate was returned to glass vial and approximately 30 to 75 mg more dimebon dihydrochloride was added. Solution was capped and stirred under ambient conditions for 23 days. Solid was collected using vacuum filtration on a 0.45 μm PTFE membrane filter. Sample was identified as Form B using PXRD.

[00119] Method 2 - Approximately 30 mg of dimebon dihydrochloride was placed in a

4 mL glass scintillation vial. 2 mL of acetonitrile was added and saturated solution was capped and stirred overnight. Solid was recovered from solution using centrifugal filtration in microcentrifuge tubes equipped with 0.45 μm nylon filter membrane inserts. PXRD of the wetcake sample and sample dried in a 55 ⁰C vacuum oven for approximately 30 minutes revealed material was of poor crystalline quality and form was not conclusively defined. All solid was returned to the filtrate. Approximately 30 to 75 mg more dimebon dihydrochloride was added and solution was capped and stirred under ambient condition for 23 days. Solid was collected using vacuum filtration on a 0.45 μm PTFE membrane filter. Sample was identified as Form B using PXRD.

[00120] Figure 6 and Table 6 and Table 7 below provide PXRD data collected for

Form B. [00121] Solid-state NMR Instrument Method: Approximately 80 mg of sample were tightly packed into a 4 mm ZrO₂ rotor. A rotor cap fitted with O-rings was used to seal the rotor. Spectra were collected at ambient pressure on a Bruker-Biospin 4 mm BL HFX CPMAS probe positioned into a wide -bore Bruker-Biospin Avance DSX 500 MHz (¹H frequency) NMR spectrometer. The sample was cooled with a direct stream of nitrogen onto the rotor having an output temperature of 10°C at a flow rate of 1200 liters/hour. The packed rotor was oriented at the magic angle and spun at 15.0 kHz. The ¹³C solid state spectrum was collected using a proton decoupled cross-polarization magic angle spinning experiment (CPMAS). The cross-polarization contact time was set to 2.0 ms. A proton decoupling field of approximately 85 kHz was applied. 5,120 scans were collected with recycle delay of 4.0 seconds. The carbon spectrum (Figure 7 and Table 8) was referenced using an external standard of crystalline adamantane, setting its upfield resonance to 29.5 ppm.

Table 6. Form B PXRD Peaks

Table 7. Form B Unique PXRD Peaks

Table 8. Carbon chemical shifts observed for dimebon dihydrochloride Form B hemi-hydrate.

(a) Referenced to external sample of solid phase adamantane at 29.5 ppm.

(b) Defined as peak heights. Intensities can vary depending on the actual setup of the CPMAS experimental parameters and the thermal history of the sample. CPMAS intensities are not necessarily quantitative.

*Peak shoulder Example 1OC: Preparation, powder x-ray diffraction, and ssNMR for Dimebon Dihydrochloride Form C monohydrate

[00122] 285 mg of dimebon dihydrochloride dihydrate was weighed into a 20 rnL glass scintillation vial. Approximately 20 mL IPA was added. Solution was capped and stirred under ambient conditions for 13 days. Solid was recovered using vacuum filtration on a 0.45 PTFE filter membrane. Solid was dried in a vacuum dessicator for approximately 30 minutes. Sample was identified as Form C by PXRD. See Figure 8, and Table 9 and Table 10 below.

[00123] Solid-state NMR Instrument Method: Approximately 80 mg of sample were tightly packed into a 4 mm ZrO₂ rotor. A rotor cap fitted with O-rings was used to seal the rotor. Spectra were collected at ambient pressure on a Bruker-Biospin 4 mm BL HFX CPMAS probe positioned into a wide -bore Bruker-Biospin Avance DSX 500 MHz (¹H frequency) NMR spectrometer. The sample was cooled with a direct stream of nitrogen onto the rotor having an output temperature of 10°C at a flow rate of 1200 liters/hour. The packed rotor was oriented at the magic angle and spun at 15.0 kHz. The ¹³C solid state spectrum was collected using a proton decoupled cross-polarization magic angle spinning experiment (CPMAS). The cross-polarization contact time was set to 2.0 ms. A proton decoupling field of approximately 85 kHz was applied. 4,352 scans were collected with recycle delay of 9.7 seconds. The carbon spectrum (Figure 9 and Table 11) was referenced using an external standard of crystalline adamantane, setting its upfield resonance to 29.5 ppm.

Table 9. Form C Peaks

Table 11. Carbon chemical shifts observed for dimebon dihydrochloride Form C monohydrate

(a) Referenced to external sample of solid phase adamantane at 29.5 ppm.

(b) Defined as peak heights. Intensities can vary depending on the actual setup of the CPMAS experimental parameters and the thermal history of the sample. CPMAS intensities are not necessarily quantitative.

*Peak shoulder

Example 10D: Preparation, powder x-ray diffraction, and ssNMR for Dimebon

Dihydrochloride Form D dihydrate

[00124] The powder X-ray diffraction data for Dimebon Dihydrochloride Form D dihydrate is shown in Figure 10 and Table 12 and Table 13 below.

[00125] Solid-state NMR Instrument Method: Approximately 80 mg of sample were tightly packed into a 4 mm ZrO₂ rotor. A rotor cap fitted with O-rings was used to seal the rotor. Spectra were collected at ambient pressure on a Bruker-Biospin 4 mm BL HFX CPMAS probe positioned into a wide -bore Bruker-Biospin Avance DSX 500 MHz (¹H frequency) NMR spectrometer. The sample was cooled with a direct stream of nitrogen onto the rotor having an output temperature of 10°C at a flow rate of 1200 liters/hour. The packed rotor was oriented at the magic angle and spun at 15.0 kHz. The ¹³C solid state spectrum was collected using a proton decoupled cross-polarization magic angle spinning experiment (CPMAS). The cross-polarization contact time was set to 2.0 ms. A proton decoupling field of approximately 85 kHz was applied. 5,120 scans were collected with recycle delay of 4.2 seconds. The carbon spectrum (Figure 11 and Table 14) was referenced using an external standard of crystalline adamantane, setting its upfield resonance to 29.5 ppm.

Table 12. Form D Peaks

Table 14. Carbon chemical shifts observed for dimebon dihydrochloride Form D dihydrate

(a) Referenced to external sample of solid phase adamantane at 29.5 ppm.

(b) Defined as peak heights. Intensities can vary depending on the actual setup of the CPMAS experimental parameters and the thermal history of the sample. CPMAS intensities are not necessarily quantitative.

*Peak shoulder

Example 1OE: Preparation, powder x-ray diffraction, and ssNMR for amorphous

Dimebon Dihydrochloride

[00126] 1.47 g of dimebon dihydrochloride dihydrate was weighed into a 100 mL round bottomed flask. Approximately 40 mL methanol was added to flask and all solid dissolved. Solvent was evaporated at approximately 55 ⁰C at 100 mBar. Yellowish glassy material remained. PXRD revealed the powder was amorphous; see Figure 12. [00127] Solid-state NMR Instrument Method: Approximately 80 mg of sample were tightly packed into a 4 mm ZrO₂ rotor. A rotor cap fitted with O-rings was used to seal the rotor. Spectra were collected at ambient pressure on a Bruker-Biospin 4 mm BL HFX CPMAS probe positioned into a wide -bore Bruker-Biospin Avance DSX 500 MHz (¹H frequency) NMR spectrometer. The sample was cooled with a direct stream of nitrogen onto the rotor having an output temperature of 10°C at a flow rate of 1200 liters/hour. The packed rotor was oriented at the magic angle and spun at 15.0 kHz. The ¹³C solid state spectrum was collected using a proton decoupled cross-polarization magic angle spinning experiment (CPMAS). The cross-polarization contact time was set to 2.0 ms. A proton decoupling field of approximately 85 kHz was applied. 15,360 scans were collected with recycle delay of 3.6 seconds. The carbon spectrum (Figure 13 and Table 15) was referenced using an external standard of crystalline adamantane, setting its upfield resonance to 29.5 ppm.

Table 15. Carbon chemical shifts observed for amorphous dimebon dihydrochloride

(a) Referenced to external sample of solid phase adamantane at 29.5 ppm.

(b) Defined as peak heights. Intensities can vary depending on the actual setup of the CPMAS experimental parameters and the thermal history of the sample. CPMAS intensities are not necessarily quantitative.

*Peak shoulder

Example 1OF: Preparation, powder x-ray diffraction, and ssNMR for Dimebon

Dihydrochloride Form F trihydrate

[00128] Approximately 230 mg of dimebon dihydrochloride dihydrate was placed in a mortar. Methanol was dripped onto sample until solid had dissolved. Solution was ground with a mortar in the hood until all of the solvent had evaporated leaving behind a whitish powder. Material was identified as Form F by PXRD. See Figure 14 and Table 16 and Table 17 below.

[00129] Solid-state NMR Instrument Method: Approximately 80 mg of sample were tightly packed into a 4 mm ZrO₂ rotor. A rotor cap fitted with O-rings was used to seal the rotor. Spectra were collected at ambient pressure on a Bruker-Biospin 4 mm BL HFX CPMAS probe positioned into a wide -bore Bruker-Biospin Avance DSX 500 MHz (¹H frequency) NMR spectrometer. The sample was cooled with a direct stream of nitrogen onto the rotor having an output temperature of 10°C at a flow rate of 1200 liters/hour. The packed rotor was oriented at the magic angle and spun at 15.0 kHz. The ¹³C solid state spectrum was collected using a proton decoupled cross-polarization magic angle spinning experiment (CPMAS). The cross-polarization contact time was set to 2.0 ms. A proton decoupling field of approximately 85 kHz was applied. 4,352 scans were collected with recycle delay of 2.0 seconds. The carbon spectrum (Figure 15 and Table 18) was referenced using an external standard of crystalline adamantane, setting its upfield resonance to 29.5 ppm. Table 16. Form F Peaks

Table 18. Carbon chemical shifts observed for dimebon dihydrochloride Form F trihydrate

(a) Referenced to external sample of solid phase adamantane at 29.5 ppm.

(b) Defined as peak heights. Intensities can vary depending on the actual setup of the CPMAS experimental parameters and the thermal history of the sample. CPMAS intensities are not necessarily quantitative.

*Peak shoulder

[00130] The disclosures of all publications, patents, patent applications and published patent applications referred to herein by an identifying citation are hereby incorporated herein by reference in their entireties.

[00131] Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it is apparent to those skilled in the art that certain changes and modifications will be practiced. Therefore, the description and examples should not be construed as limiting the scope of the invention.

Claims

CLAIMSWhat is claimed is:

1. A method of making a pyridylethyl-substituted carboline or salt thereof or solvate of any of the foregoing, comprising reacting a carboline compound with no more than about four equivalents of methyl vinyl pyridine to produce the pyridylethyl-substituted carboline.

2. The method of claim 1. wherein the method is carried out in the presence of a base selected from the group consisting of KOH, K₃PO₄, tBuOK, tBuONa, tBuOLi, EtOK, EtONa, EtOLi, MeOK, and MeONa.

3. The method of claim 1. wherein the carboline compound is reacted with no more than about three molar equivalents of methyl vinyl pyridine.

4. The method of claim 3. wherein the carboline compound is reacted with no more than about two molar equivalents of methyl vinyl pyridine.

5. The method of claim 1, comprising reacting a carboline compound of the form:

where Ri is Me, Et or PhCH₂ , and R₃ is H, Me or Br, with a vinyl pyridine compound of the form:

in the presence of a base, to form a pyridy Ie thy 1- substituted carboline compound of the formula:

or a salt, a hydrate, or a combined salt/hydrate thereof.

6. The method of claim 5, wherein the pyridylethyl-substituted carboline compound is formed in a yield of about 60% or greater.

7. The method of claim 6, where the carboline compound is 2,8-dimethyl-2,3,4,5-tetrahydro- lH-pyrido[4,3-b]indole.

8. The method of claim 6, where the solvent used for the reaction is selected from the group consisting of N-methyl pyrrolidone (NMP), dimethyl acetamide (DMAC), and diglyme (bis(2-methoxy ethyl ether).

9. The method of claim 6, where the base is selected from the group consisting of KOH, K₃PO₄, tBuOK, tBuONa, tBuOLi, EtOK, EtONa, EtOLi, MeOK, and MeONa.

10. The method of claim 6, where the reaction of the carboline compound with the vinyl pyridine compound is carried out at a temperature of about 80 ⁰C to about 130 ⁰C.

11. The method of claim 6, where the reaction is performed for about 8 hours to about 26 hours.

12. The method of claim 6, where the carboline compound is 2,8-dimethyl-2,3,4,5- tetrahydro-lH-pyrido[4,3-b]indole and the vinyl pyridine compound is 2-methyl-5- vinylpyridine (MVP), where about 1.5 equivalent MVP, about 1 equivalent 2,8-dimethyl- 2,3,4,5-tetrahydro-lH-pyrido[4,3-b]indole free base and about 0.5 equivalent of tBuOK in DMAC or diglyme are reacted at about 100⁰C - about 12O⁰C for about 8 hours.

13. The method of claim 6, where the carboline compound is 2,8-dimethyl-2,3,4,5- tetrahydro-lH-pyrido[4,3-b]indole and the vinyl pyridine compound is 2-methyl-5- vinylpyridine (MVP), where about 1.5 equivalent MVP, about 1 equivalent 2,8-dimethyl- 2,3,4,5-tetrahydro-lH-pyrido[4,3-b]indole HCl salt, and about 1.7 equivalent tBuOK in DMAC or diglyme are reacted at about 100 ⁰C to about 120 ⁰C for about 8 hours.

14. The method of claim 6, where the carboline compound is 2,8-dimethyl-2,3,4,5- tetrahydro-lH-pyrido[4,3-b]indole and the vinyl pyridine compound is 2-methyl-5- vinylpyridine (MVP), where about 1.75 equivalent MVP, about 1 equivalent 2,8-dimethyl- 2,3,4,5-tetrahydro-lH-pyrido[4,3-b]indole free base, and about 1.8 equivalent K₃PO₄ in DMAC are reacted at about 120 ⁰C for about 18 hours.

15. A solid form of dimebon, comprising anhydrous dimebon dihydrochloride.

16. A solid form of dimebon, consisting essentially of anhydrous dimebon dihydrochloride.

17. The solid form of dimebon of claim 15 or 16, characterized by having carbon solid state NMR peaks at about 147.1, about 124.0, about 111.1, and about 21.6 ppm, referenced to an external sample of solid phase adamantane at 29.5 ppm.

18. A solid form of dimebon, comprising dimebon dihydrochloride hemi-hydrate.

19. A solid form of dimebon, consisting essentially of dimebon dihydrochloride hemi- hydrate.

20. The solid form of dimebon of claim 18 or 19, characterized by having carbon solid state NMR peaks at about 148.5, about 133.8, about 117.0, and about 17.6 ppm, referenced to an external sample of solid phase adamantane at 29.5 ppm.

21. A solid form of dimebon, comprising dimebon dihydrochloride monohydrate.

22. A solid form of dimebon, consisting essentially of dimebon dihydrochloride monohydrate.

23. The solid form of dimebon of claim 21 or 22, characterized by having carbon solid state NMR peaks at about 152.9, about 118.7, about 113.4, about 38.4, and about 30.2 ppm, referenced to an external sample of solid phase adamantane at 29.5 ppm.

24. A solid form of dimebon, comprising dimebon dihydrochloride trihydrate.

25. A solid form of dimebon, consisting essentially of dimebon dihydrochloride trihydrate.

26. The solid form of dimebon of claim 24 or 25, characterized by having carbon solid state NMR peaks at about 147.5, about 130.6, about 123.7, and about 44.7 ppm, referenced to an external sample of solid phase adamantane at 29.5 ppm.

27. A solid form of dimebon, comprising amorphous dimebon dihydrochloride.

28. A solid form of dimebon, consisting essentially of amorphous dimebon dihydrochloride.

29. The solid form of dimebon of claim 27 or 28, characterized by having carbon solid state NMR peaks at about 151.5, about 125.0, about 111.3, and about 21.3 ppm, referenced to an external sample of solid phase adamantane at 29.5 ppm.

30. A composition comprising one or more solid forms of dimebon according to claims 16- 29, additionally comprising a pharmaceutically acceptable carrier.