HK1159065A1 - Method for manufacturing neuraminic acid derivatives - Google Patents

Description

[Technical Field]

The present invention relates to a method for manufacturing an ortho ester compound, useful in the manufacture of neuraminic acid derivatives which have neuraminidase inhibitory activity.

[Background Art]

A compound represented by the formula (I): [wherein R¹ represents a C₁-C₁₉ alkyl group and R² represents a C₁-C₄ alkyl group] or a pharmacologically acceptable salt thereof is known to have excellent neuraminidase inhibitory activity and therefore to be useful as a drug for treatment or prevention of influenza (Patent Document 1 or 2).

A trifluoroacetic acid salt of a compound represented by the formula (III): is known to have excellent neuraminidase inhibitory activity and therefore to be useful as a drug for treatment or prevention of influenza (Non-patent Document 1 or 2).

[Patent Document 1] US Patent No. 6340702 (corresponding to Japanese Patent No. 3209946 )

[Patent Document 2] US Patent No. 6844363 (corresponding to Japanese Patent Application No. 2002-012590 )

[Non-patent Document 1] T. Honda et al., Bioorganic Medicinal Chemistry Letters, 2002, pp. 1921-1924

[Non-patent Document 2] T. Honda et al., Bioorganic Medicinal Chemistry Letters, 2002, pp. 1925-1928

Further references are: (a) Alaux et al., "J. Med. Chem.", 48, 2005, pages 7980-7992; (b) Stanoeva et. al., "Tetrahedron", 60(23), 2004, pages 5077-5084; (c) Peter et. al., "J. Am. Chem. Soe.", 50,1928, pages 516-518; (d) Reitter et. al., "Chemische Berichte", 40, 1907, pages 3020-3025.

As a result of conducting extensive studies on methods for manufacturing neuraminic acid derivatives, the inventors of the present invention have found a novel method for manufacturing an ortho ester compound useful in the manufacture of neuraminic acid derivatives, and have found that the compound can be obtained in high yield by the manufacturing method. The present invention has been completed based on the aforementioned findings.

[Summary of the Invention]

The present invention provides

1. [1] a method for manufacturing a compound represented by the formula R¹C(OR⁷)₃ (compound (14)) wherein R¹ represents a C₁-C₁₉ alkyl group and R⁷ represents a C₁-C₆ alkyl group, comprising: allowing a compound represented by the formula (15): wherein R¹ represents a C₁-C₁₉ alkyl group, R⁷ represents a C₁-C₆ alkyl group, and X represents Cl, Br. I, HSO₄ or NO₃, to react with a compound represented by the formula R⁷-OH wherein R⁷ represents a C₁-C₆ alkyl group, in a solvent which forms a bilayer system.
2. [2] the manufacturing method as described in [1], wherein the solvent which forms the bilayer system is a hydrocarbon,
3. [3] the manufacturing method as described in [1], wherein the solvent which forms the bilayer system is cyclohexane or methylcyclohexane, and
4. [4] the manufacturing method as described in any one of [1] through [3], wherein R¹ is a 1-heptyl group, R⁷ is a methyl group, and X is Cl.

In the present invention, "C₁-C₁₉ alkyl group" of R¹ represents a linear or branched alkyl group having 1 to 19 carbon atoms, and may be for example, a methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decanyl group, undecanyl group, dodecanyl group, tridecanyl group, tetradecanyl group, pentadecanyl group, hexadecanyl group, heptadecanyl group, octadecanyl group or nonadecanyl group, preferably a C_s-C₁₉ alkyl group, more preferably a C₅-C₁₇ alkyl group, even more preferably a pentyl group, heptyl group, nonyl group, undecanyl group, tridecanyl group, pentadecanyl group or heptadecanyl group, further preferably a 1-pentyl group, 1-heptyl group, 1-nonyl group, 1-undecanyl group, 1-tridecanyl group, 1-pentadecanyl group or 1-heptadecanyl group, and most preferably a 1-heptyl group.

-C₁-C₆ alkyl group" in R⁷ is a linear or branched alkyl group having 1 to 6 carbon atoms, and may be for example, a methyl group, ethyl group, propyl group, butyl group, pentyl group or hexyl group, preferably a C₁-C₄ alkyl group, more preferably a methyl group or ethyl group, and most preferably a methyl group.

In the production of compound (14), when a compound represented by the formula R⁷-OH is used as a reagent and as a solvent to react with compound (15), following a publicly known method (Journal of American Chemical Society, 1942, vol, 64, pp.1825-1827), the yield of compound (14) is approximately 35% to 50% (refer to Comparative Example 1).

In contrast, when compound (15) is allowed to react with a compound represented by the formula R⁷-OH in a solvent which forms a bilayer system, the yield of compound (14) is improved remarkably to approximately 80% to 85% (refer to Example 1). Therefore, the manufacturing method of compound (14) from compound (15) provides an efficient method of manufacturing compound (14), which may be used in the production of compound (I).

[Detailed Description of the preferred Embodiments]

In the present invention, the method of manufacturing can be conducted in accordance with the following Process G.

Process G

In Process G, R¹, R⁷, and X have the same meanings as described above.

The solvent used in the reactions of each of the steps of Process G is not limited so long as it does not inhibit the reaction and dissolves the starting material to some degree, and can be, for example, selected from the following solvent group. The solvent group comprises aliphatic hydrocarbons such as hexane, pentane, petroleum ether and cyclohexane; aromatic hydrocarbons such as benzene, toluene and xylene; halogenated hydrocarbons such as methylene chloride, chloroform, carbon tetrachloride, dichloroethane, chlorobenzene and dichlorobenzene; ethers such as diethyl ether, diisopropyl ether, tetrahydrofuran, dioxane, dimethoxyethane and diethyleneglycol dimethyl ether; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; esters such as ethyl acetate, propyl acetate and butyl acetate; nitriles such as acetonitrile, propionitrile, butyronitrile and isobutyronitrile; carboxylic acids such as acetic acid and propionic acid; alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol and 2-methyl-2-propanol; amides such as formamide. N,N-dimethylformamide. N,N-dimethylacetamide, N-methyl-2-pyrrolidone and hexamethylghosphoroamide; sulfoxides such as dimethyl sulfoxide; sulfones such as sulforane; water; and mixtures thereof.

In the reactions of each of the steps of Process G, the reaction temperature differs depending on solvent, starting material, reagent and the like, and is selected appropriately. In addition, the reaction time differs depending on solvent, starting material, reagent and the like, and is selected appropriately.

In the reactions of each of the steps of Process G, the desired compound of each of the steps can be isolated from a reaction mixture in accordance with ordinary methods after completion of the reaction. The desired compound may be obtained by, for example, (i) removing insoluble matters such as catalyst as necessary, (ii) extracting the desired compound by adding water and solvent which is immiscible with water (for example, ethyl acetate and the like) to the reaction mixture, (iii) washing the organic layer with water and drying it as necessary by using a drying agent such as anhydrous magnesium sulfate, and (iv) distilling off the solvent. The obtained desired compound can be further purified as necessary, by ordinary methods (for example, recrystallization, reprecipitation, or silicagel column chromatography). In addition, the desired compound of each procedure can also be used in the subsequent reaction without purification.

(Process G)

Process G shows a method of manufacturing compound (14) and compound (15).

(Step G-1)

Step G-1 is a procedure to allow compound (26) to react with a compound represented by the formula R⁷OH in the presence of an acid represented by the formula HX, to produce compound (15). Compound (26) is either publicly known, or can easily be produced from a publicly known compound.

In Step G-1, the acid represented by the formula HX is preferably hydrogen chloride. In Step G-1, the compound represented by the formula R⁷OH is preferably methanol.

The solvent used is preferably an ester, an aliphatic hydrocarbon, or an aromatic hydrocarbon, more preferably an ester, and most preferably methyl acetate.

The reaction temperature is preferably -50°C to 50°C, and more preferably -20°C to 20°C.

The reaction time is preferably 1 to 100 hours, and more preferably 5 to 50 hours.

(Step G-2)

Step G-2 is a procedure to allow compound (15) to react with a compound represented by the formula R⁷OH to produce compound (14).

In Step G-2, the compound represented by the formula R⁷OH is preferably methanol. R⁷ in the compound represented by the formula R⁷OH is preferably the same as R⁷ of compound (15). The volume ratio of the compound represented by the formula R⁷OH with respect to compound (15) is preferably 0.5 to 5, and more preferably 1 to 3.

The solvent used is preferably a solvent which forms a bilayer system. Here, formation of a bilayer system means that the compound represented by the formula R⁷OH in the reaction solution and the solvent form two layers that are not uniform and are separate from each other, and by stirring the reaction solution adequately, the compound present in the reaction solution, depending on its lipid solubility or water solubility, can move to the other layer in which the compound can be dissolved more easily. The solvent used is preferably a hydrocarbon, more preferably an aliphatic hydrocarbon or an aromatic hydrocarbon, even more preferably an aliphatic hydrocarbon, further preferably cyclohexane, methylcyclohexane or ethylcyclohexane, particularly preferably cyclohexane or methylcyclohexane, and most preferably methylcyclohexane. The compound represented by the formula R⁷OH in excess amount can also be used as the solvent.

The mixing ratio (volume ratio) of methylcyclohexane and methanol is preferably 10:1 to 1:2, and more preferably 5:1 to 1:1.

The reaction temperature is preferably -20°C to 90°C, and more preferably 10°C to 60°C.

The reaction time is preferably 30 minutes to 30 hours, and more preferably 2 to 15 hours.

[Examples]

The present invention will be described in more detail with reference to the following Examples; however, the scope of the present invention is not limited to these.

(Example 1) Synthesis of trimethyl orthooctanoate (compound (14) [R¹ = 1-heptyl group, R⁷= methyl group]) Step G-1: Methyl octanimidate hydrochloride

Methanol (2.81 g) and methyl acetate (30 ml) were added to octanenitrile (10.00 g), and the mixture was cooled to 0°C. Hydrogen chloride (7.50 g) was added and the mixture was stirred for 25 hours at the same temperature. Methylcyclohexane (60 ml) was added to the reaction solution, and then the solvent was distilled off under reduced pressure. Methylcyclohexane (20 ml) was added to the residue, the mixture was stirred for 1.5 hours at room temperature, and then crystals were filtered. The crystals were washed with methylcyclohexane and dried under reduced pressure to give the title compound as a white solid (14.45 g, 93.4% yield). MS (FAB): m/z 158 [M+H]⁺ HRMS (ESI): Exact mass calcd for C₉H₂₀NO [M+H]⁺ 158.15449, Found 158.15433 IR (KBr): 3139, 3109, 2925, 2857, 1712, 1627, 1474, 1411, 1213, 1100 cm^{-1 1}H NMR (CDCl₃, 500 MHz): 0.82 (3H, t, J = 7.0 Hz), 1.19 - 1.33 (8H, m). 1.67 (2H, tt, J = 7.5, 7.8 Hz), 2.70 (2H, t, J = 7.8 Hz). 4.24 (3H, s), 11.52 (18, brs), 12.46 (1H, brs). ¹³C NMR (CDCl₃, 125 MHz): 14.1, 22.6, 25.7, 28.7, 28.8, 31.5. 32.9, 60.7, 180.5.

Step G-2: Trimethyl orthooctanoate (compound (14) [R¹ = 1-heptyl group, R⁷ m methyl group])

Methylcyclohexane (240 ml) and methanol (80 ml) were added to the compound (40.00 g) obtained in Step G-1, and the mixture was stirred for 6 hours at 35°C. The reaction solution was cooled to 10°C, and methylcyclohexane (20 ml) was added, followed by washing with 5% aqueous sodium hydrogencarbonate (280 ml). The reaction solution was further washed with 5% aqueous sodium hydrogencarbonate (120 ml), and the organic layer was separated. The insoluble matter was filtered, and the residue was washed with methylcyclohexane (20 ml). Then, the filtrate and the solution used for washing were combined, and the solvent was distilled off under reduced pressure. The residue was purified by distillation under reduced pressure (1.5-1.8 torr, b.p. 85-90°C) to give the title compound as a colorless transparent oil (35.37 g, 83.8% yield). MS (ESI): m/z 227 [M+Na]⁺ HRMS (ESI): Exact mass calcd for C₁₁H₂₄O₃Na [M+Na]⁺227.16231, Found 227.16138 IR (neat): 2955, 2928, 2854, 1466, 1241, 1153, 1078, 1047, 977 cm^{-1 1}H NMR (CDCl₃, 500 MHz): 0.86 (3H, t, J = 6.8 Hz), 1.23 - 1.33 (8H, m), 1.67 - 1.71 (2H, m), 3.21 (9H, s). ¹³C NMR (CDCl₃, 125 MHz): 14.1, 22.7, 22.8, 29.3, 29.5, 30.5, 31.9, 49.4, 116.0.

(Comparative Example 1) Synthesis of trimethyl orthooctanoate (compound (14)[R¹ = 1-heptyl group, R⁷ = methyl group])

Methanol (330 ml) and petroleum ether (1 L) were added to the compound (160.44 g) obtained in accordance with Step G-1 of Example 1, and the mixture was stirred for 18 hours under reflux. The reaction solution was cooled to 0°C, and was allowed to stand for 2 hours at the same temperature. The insoluble matter was filtered, and the solvent was distilled off under reduced pressure. The residue was purified by distillation under reduced pressure (2.2 torr, b.p. 93-96°C) to give the title compound as a colorless transparent oil (78.60 g, 44.7% yield).

Claims (4)

1. A method of manufacturing a compound represented by the formula R¹C(OR⁷)₃ wherein R¹ represents a C₁-C₁₉ alkyl group and R⁷ represents a C₁-C₆ alkyl group, comprising:

   allowing a compound represented by the formula (15): wherein R¹ represents a C₁-C₁₉ alkyl group, R⁷ represents a C₁-C₆ alkyl group and X represents Cl, Br, I, HSO₄ or NO₃, to react with a compound represented by the formula R⁷-OH wherein R⁷ represents a C₁-C₆ alkyl group, in a solvent which forms a bilayer system.
2. The manufacturing method according to Claim 1, wherein the solvent which forms the bilayer system is a hydrocarbon.
3. The manufacturing method according to Claim 1, wherein the solvent which forms the bilayer system is cyclohexane or methylcyclohexane.
4. The manufacturing method according to any one of Claims 1 to 3, wherein R¹ is a 1-heptyl group, R⁷ is a methyl group and X is Cl.