WO1999039207A1

WO1999039207A1 - Acid cleavable phenoxyalkyl linker for combinatorial synthesis

Info

Publication number: WO1999039207A1
Application number: PCT/US1999/001370
Authority: WO
Inventors: Ge Li; Zhen Min He
Original assignee: Pharmacopeia Inc
Current assignee: Pharmacopeia LLC
Priority date: 1998-01-29
Filing date: 1999-01-21
Publication date: 1999-08-05
Anticipated expiration: 2000-07-29
Also published as: AU2335899A

Abstract

A substrate for solid phase synthesis of formula (I) is disclosed. Also disclosed are processes for preparing the substrate and intermediates useful therein. Among the novel intermediates are compounds of formula (II) wherein n is 3-20; R is OH, an activated ester or the residue of a solid support having a plurality of amino functionalities; R1 is lower alkyl or phenyl; R2 is lower alkyl or phenyl; and R3 is lower alkyl, phenyl or lower alkoxy.

Description

ACID CLEAVABLE PHENOXYALKYL LINKER FOR COMBINATORIAL SYNTHESIS

TECHNICAL FIELD

This invention relates generally to the synthesis of chemical compounds, and more particularly, to the solid phase synthesis of combinatorial libraries of chemical compounds.

BACKGROUND OF THE INVENTION

Combinatorial organic synthesis is becoming an important tool in drug discovery. Methods for the synthesis of large numbers of diverse compounds have been described [EUman, et. al. Chem. Rev. 96: 555-600 (1996)], as have methods for tagging systems [Ohlmeyer et al, Proc. Natl. Acad. Sci. USA, 90, 10922- 10926, (1993)]. The growing importance of combinatorial synthesis has created a need for new resins and linkers having chemical and physical properties to accommodate a wide range of conditions, since success depends on the ability to synthesize diverse sets of molecules on a solid support and to then cleave those molecules cleanly and in good yield.

Linkers are molecules that can be attached to a solid support and to which the desired members of a library of chemical compounds may in turn be attached. When the construction of the library is complete, the linker allows clean separation of the target compounds from the solid support without harm to the compounds and preferably without damage to the support. Several linkers have been described in the literature. Their success relies on having sufficient stability to allow the steps of combinatorial synthesis under conditions that will not cleave the linker, while still having a fairly high lability under at least one set of conditions that is not employed in the synthesis. For example, if an acid labile linker is employed, then the combinatorial synthesis must be restricted to reactions that do not require the -2-

presence of an acid of sufficient strength to endanger the integrity of the linker. This sort of balancing act often imposes serious constraints on the reactions that can be employed in preparing the library.

The 4-[4-(hydroxymethyl)-3-methoxyphenoxy]butyryl residue is a known linker, which is attached to a solid support having amino functionalities by forming an amide with the carboxyl of the butyric acid chain. N-Protected amino acids are attached to the hydroxyl of the 4-hydroxymethyl group via their carboxyl to form 2,4-dialkoxybenzyl esters, which can be readily cleaved in acid media when the synthesis is complete [see for example Riniker et al. Tetrahedron 49 9307-9312 (1993)]. The drawback to such esters is that they can also be cleaved by many of the reagents that one might want to use in combinatorial synthesis.

A somewhat more stable ester is formed from 4-[4- (hydroxymethyl)phenoxy]butyric acid. It has been described in European published application EP 445915. In this case, the ester was cleaved with a 90:5:5 mixture of trifluoroacetic acid, dimethyl sulfide and thioanisole.

When the desired product is a peptide amide, the 4-[4-(formyl)-3,5- dimethoxyphenoxy]butyryl residue has been employed. It is attached to a solid phase substrate via the carboxyl of the butyric acid chain, and the 4-aldehyde is reductively aminated. N-Protected amino acids are then reacted with the alkylamine via their carboxyl to form 2,4,6-trialkoxybenzylamides. These may be cleaved by 1: 1 trifluoroacetic acid in dichloromethane. [See PCT application WO97/23508.]

It would be useful to have a linker-resin combination that could be reacted directly with a phenol, that would withstand many of the reaction conditions employed in combinatorial synthesis, and that is readily and cleanly cleavable to release a phenol SUMMARY OF THE INVENTION

The present invention relates to a linker-resin combination that demonstrates the ability to withstand many of the common reaction conditions and is cleavable to release a phenol under conditions that do not diminish the chemical integrity of the desired products.

In one aspect, the invention relates to a substrate for solid phase synthesis comprising a solid phase-linker combination of the formula:

-(CH₂)_n — CH₂X

in which ( j — NH represents the residue of a solid support having a plurality

of amino functionalities and the remainder constitutes the linker. In these solid phase-linker combinations X is bromo, chloro, mesylate or tosylate, and n is 3-20, preferably 3-5. Preferred solid phases are aminomethylated poly(styrene-co- divinylbenzene) and divinylbenzene-cross-linked, polyethyleneglycol-grafted polystyrene functionalized with amino groups. In a preferred linker, X is bromo.

In another aspect, the invention relates to chemical intermediates of the formula

O Si— R²

R³

wherein n is 3-20; R is OH, the residue of an activated ester or the residue of a solid support having a plurality of amino functionalities; R¹ is lower alkyl or phenyl; -4-

R² is lower alkyl or phenyl; and R³ is lower alkyl, phenyl or lower alkoxy. In preferred embodiments R¹ and R² are methyl and R³ is t-butyl.

In another aspect, the invention relates to processes for preparing the foregoing substrate for solid phase synthesis. One process comprises: (a) combining the foregoing chemical intermediate, in which R is OH, and the solid support having amino functionality in an inert solvent in the presence of condensing agents to provide a silylated precursor of a substrate for solid phase synthesis of formula

Λ R¹

O Si— R

R³ wherein R is the residue of the amino functional solid support; (b) treating the silylated precursor with a reagent capable of cleaving a silyl ether to provide a benzyl alcohol precursor of a substrate for solid phase synthesis; and (c) treating the benzyl alcohol precursor with an excess of a brominating reagent in an inert solvent to provide the substrate for solid phase synthesis. In an alternative process, in step (a) a subset of R, namely R⁴, is a group displaceable by an amine and no condensing agent is needed. Typically R⁴ will be an activated ester. In preferred processes the reagent capable of cleaving a silyl ether is a tetraalkylammonium fluoride and the brominating reagent is phosphorus tribromide.

In another aspect, the invention relates to a process for preparing a compound of formula o

HO— L_(CH₂)_n o

-5-

comprising:

(a) reacting a lower alkyl ω-haloalkylcarboxylate with about one equivalent of 4-hydroxybenzyl alcohol in an inert solvent in the presence of at least one equivalent of an alkali metal carbonate to provide a lower alkyl ω-phenoxyalkylcarboxylate; (b) reacting the lower alkyl ω-phenoxyalkylcarboxylate with an excess of a silylating agent in an inert solvent to provide a silylated lower alkyl ω- phenoxyalkylcarboxylate; and

(c) cleaving lower alkyl from the silylated lower alkyl ω- phenoxyalkylcarboxylate by treatment with an excess of an alkali metal hydroxide in an aqueous solvent to provide a compound of formula

Ho— U— (CH₂)_n O— (v

-Si— R²

L

or salt thereof. In preferred embodiments, the lower alkyl ω-haloalkylcarboxylate is ethyl 4-bromobutyrate, the alkali metal carbonate is cesium carbonate, the silylating agent is a combination of t-butyldimethylsilyl chloride and imidazole, and the alkali metal hydroxide is lithium hydroxide.

-6-

DETAILED DESCRIPTION OF THE INVENTION

Abbreviations and Definitions

The following abbreviations and terms have the indicated meanings throughout:

Ac ~ acetyl

BNB = 4-bromomethyl-3-nitrobenzoic acid

Boc = t-butyloxy carbonyl

Bu = butyl c- = cyclo

DBU = diazabicyclo[5.4.0]undec-7-ene

DCM = dichloromethane = methylene chloride = CH₂C1₂

DEAD = diethyl azodicarboxylate

DIC = diisopropylcarbodiimide

DIEA = N,N-diisopropylethyl amine

DMAP = 4-N,N-dimethylaminopyridine

DMF = N,N-dimethylformamide

DMSO = dimethyl sulfoxide

DVB = 1 ,4-divinylbenzene

EEDQ = 2-ethoxy- 1 -ethoxycarbonyl- 1 ,2-dihydroquinoline

Fmoc = 9-fluorenylmethoxycarbonyl

GC = gas chromatography

HATU — O-(7- Azabenzotriazol- 1 -yl)- 1,1,3,3 -tetramethyluronium hexafluorophosphate

HOAc = acetic acid

HOBt = hydroxybenzotriazole

Me = methyl mesyl = methanesulfonyl

NMO = N-methylmorpholine oxide

PEG = polyethylene glycol

Ph =

phenyl -7-

PhOH = phenol

PfP = pentafluorophenol

PyBroP - bromo-tris-pyrrolidino-phosphonium hexafluorophosphate rt = room temperature sat'd = saturated s- = secondary t- = tertiary

TBDMS = t-butyldimethylsilyl

TFA = trifluoroacetic acid

THF = tetrahydrofuran

TMOF = trimethyl orthoformate

TMS = trimethylsilyl tosyl = p-toluenesulfonyl

Trt = triphenylmethyl

"Alkyl" is intended to include linear, or branched hydrocarbon structures and combinations thereof of 1 to 20 carbons. "Lower alkyl" means alkyl groups of from 1 to 6 carbon atoms. Examples of lower alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, s-and t-butyl, pentyl, hexyl, and the like.

"Cycloalkyl" refers to saturated hydrocarbons of from 3 to 12 carbon atoms having one or more rings. Examples of "cycloalkyl" groups include c-propyl, c- butyl, c-pentyl,c-hexyl, 2-methylcyclopropyl, cyclopropylmethyl, cyclopentylmethyl, norbornyl, adamantyl, myrtanyl and the like. "Lower cycloalkyl" refers to cycloalkyl of 3 to 6 carbons.

Ci to C₂₀ Hydrocarbon includes alkyl, cycloalkyl, alkenyl, alkynyl, aryl and combinations thereof. Examples include phenethyl, cyclohexylmethyl and naphthylethyl. "Alkoxy" means alkoxy groups of from 1 to 8 carbon atoms of a straight, branched, cyclic configuration and combinations thereof. Examples of alkoxy groups include methoxy, ethoxy, propoxy, isopropoxy, cyclopropyloxy, cyclohexyloxy, and the like. "Lower alkoxy" means alkoxy having 1-4 carbon atoms.

"Halo" includes F, Cl, Br, and I.

"Fluoroalkyl" refers to an alkyl residue in which one or more hydrogen atoms are replaced with F, for example: trifluoromethyl, difluoromethyl, and pentafluoroethyl.

"Arylalkyl" denotes a residue comprising an alkyl attached to an aryl ring.

Examples include benzyl, phenethyl, 4-chlorobenzyl, and the like.

For the purpose of the present invention, the term combinatorial library means a collection of molecules based on logical design and involving the selective combination of building blocks by means of simultaneous chemical reactions. Each species of molecule in the library is referred to as a member of the library.

As will be obvious to the person of skill in the art, the linkers of the invention could be used in combinatorial synthesis to attach tags as well as to attach the moiety of putative chemical or pharmacological interest. Tags are chemical entities which possess several properties: they are detachable from the solid supports, preferably by means orthogonal to those employed for releasing the compound of pharmacological interest; they are stable under the synthetic conditions; and they are capable of being detected at very low concentrations, e.g., 10^"18 to 10^"9 mole. Suitable tags and methods for their employment are described in US patent 5,565,324, the entire disclosure of which is incorporated herein by reference. -9-

The materials upon which the combinatorial syntheses are performed are referred to as solid supports, beads, and resins. These terms are intended to include:

(a) beads, pellets, disks, fibers, gels, or particles such as cellulose beads, pore-glass beads, silica gels, polystyrene beads optionally cross-linked with divinylbenzene and optionally grafted with polyethylene glycol, grafted co-poly beads, poly-acrylamide beads, latex beads, dimethylacrylamide beads optionally cross-linked with N,N'-bis- acryloyl ethylene diamine, glass particles coated with hydrophobic polymer, etc., i.e., material having a rigid or semi-rigid surface; and (b) soluble supports such as polyethylene glycol or low molecular weight, non-cross-linked polystyrene. The solid supports may, and usually do, have surfaces that have been functionalized with amino, hydroxy, carboxy, or halo groups; amino groups are most common. Techniques for functionalizing the surface of solid phases are well known in the art. Attachment of lysine to the surface of a bead (to increase the number of available sites) and subsequent attachment of linkers as well as further steps in a typical combinatorial synthesis are described, for example, in PCT application WO95/30642, the disclosure of which is incorporated herein by reference. In the synthesis described in WO95/30642, the linker is a photolytically cleavable linker, but the general principles of the use of a linker are well illustrated.

The invention relates to substrates for solid phase synthesis comprising solid phase-linker combinations of the formula:

O -CH₂X

In these solid phase-linker combinations, X is preferably bromo because it is most easily introduced and it reacts more rapidly and cleanly with phenols, but chloro, mesylate or tosylate could be used. The solid phase-linker combination is prepared by coupling an aminomethylated resin with a chemical intermediate of the formula -10-

HO- -(CH 2λι -O

wherein R¹ is lower alkyl or phenyl; R² is lower alkyl or phenyl; and R³ is lower alkyl, phenyl or lower alkoxy. In preferred embodiments R¹ and R² are methyl and R³ is t-butyl, but any of the well known silyl ether protecting groups can be employed. [See Greene and Wuts Protective Groups in Organic Synthesis Second Edition John Wiley & Sons, New York 1991, pages 68-86, which are incorporated herein by reference.]. The coupling involves (a) combining the foregoing chemical intermediate and the aminomethylated solid support in an inert solvent such as dichloromethane, THF or DMF, in the presence of condensing agents to provide a silylated precursor of a substrate for solid phase synthesis of formula

O Si— R^

R³

wherein R is the aminomethylated solid support; (b) treating the silylated precursor with a reagent capable of cleaving a silyl ether so as to provide a benzyl alcohol precursor of a substrate for solid phase synthesis; and (c) treating the benzyl alcohol with an excess of a brominating reagent in an inert solvent to provide the substrate for solid phase synthesis.

A reagent, as the term is used herein, refers to one or more substances that effect a chemical change. Thus, a reagent may comprise a single component, for example, phosphorus tribromide, or a plurality of components, for example, a combination of trimethylsilyl chloride and imidazole. -11-

Condensing agents for reacting amines (the resin) with carboxylic acids (the linker) are well known, particularly in the art of solid phase synthesis of peptides. Such agents include carbodiimides of various sorts, EEDQ, HATU, and the like. It is also possible to pre-react the carboxylic acid of the linker with an appropriate leaving group to form an activated ester. Activated esters denote esters which are capable of undergoing a substitution reaction with primary or secondary amines to form an amide. The term includes esters "activated" by neighboring electron withdrawing substituents. Examples include esters of phenols, particularly electronegatively substituted phenol esters such as pentafluorophenol esters; O- esters of isourea, such as arise from interaction with carbodiimides; O-esters of N- hydroxyimides and N-hydroxy heterocycles; specific examples include S-t-butyl esters, S-phenyl esters, S-2-pyridyl esters, N-hydroxypiperidine esters, N- hydroxysuccinimide esters, N-hydroxyphthalimide esters and N- hydroxybenzotriazole esters.

The reagent capable of cleaving a silyl ether can be any of those described in

Greene and Wuts, op.cit., which vary according to the nature of R¹, R² and R³ . When R¹ and R² are methyl and R³ is t-butyl (i.e. TBDMS), the ether may be cleaved by anhydrous fluoride ion, which may be provided by a tetraalkylammonium fluoride, such as tetrabutyl ammonium fluoride, in an anhydrous solvent, such as THF. Many other cleavage reagents are known for TBDMS and are possible [See Greene and Wuts, op.cit. p. 80-81.]

The hydroxyl of the benzyl alcohol may be replaced with bromine by treatment with phosphorus tribromide, as described below, or by carbon tetrabromide and a trivalent phosphorus reagent, such as triphenyl phosphine. Other residues that can be readily displaced by a phenol may also replace the hydroxyl. For example, chlorine may be introduced in an analogous fashion to that employed for bromine. The mesylate and tosylate residues may be introduced by treatment of the hydroxyl with methanesulfonyl chloride or toluenesulfonyl chloride respectively. These and other methods are well known in the art. -12-

The compounds of formula o

HO— L-₍cH₂)_n O

X_/ V X o S ii— F

employed in preparing the solid phase-linker combinations of the invention may be synthesized by:

(a) reacting a lower alkyl ω-haloalkylcarboxylate with about one equivalent of 4-hydroxybenzyl alcohol in an inert solvent in the presence of at least one equivalent of an alkali metal carbonate to provide a lower alkyl ω-phenoxyalkylcarboxylate;

(b) reacting the lower alkyl ω-phenoxyalkylcarboxylate with an excess of a silylating reagent in an inert solvent to provide a silylated lower alkyl ω- phenoxyalkylcarboxylate; and

(c) cleaving lower alkyl from the silylated lower alkyl ω- phenoxyalkylcarboxylate by treatment with an excess of an alkali metal hydroxide in an aqueous solvent.

Lower alkyl ω-haloalkylcarboxylates are readily prepared by procedures known in the art, and most of those in the C-4 to C-10 range are commercially available. In preferred embodiments, the lower alkyl ω-haloalkylcarboxylate is ethyl 4-bromobutyrate. It is desirable to employ a base in the reaction of the haloalkylcarboxylate with the phenol. Alkali metal carbonates are simple to use and cheap, but other bases could be used, including organic bases. A preferred alkali metal carbonate is cesium carbonate.

The silylating conditions that we have employed are excess t- butyldimethylsilyl chloride in the presence of excess imidazole, but other conditions are described in Greene and Wuts and could be used. Many silylations, particularly those with silyl chlorides, are best run in the presence of at least one equivalent of a weak base. -13-

Saponification of the lower alkyl ester may be accomplished most cleanly with lithium hydroxide, but other alkali metal hydroxides could also be used and the pH may be controlled, e.g. by means of an autotitrator.

In a particular embodiment, the invention relates to a process for preparing a substrate for solid phase synthesis of the formula:

-N- -(CH 2^n -CH₂Br H

wherein n is 3-5 comprising

(a) combining an excess of dialkylcarbodiimide, an excess of hydroxybenzotriazole, a solid support having a plurality of amino functionalities on its surface, and an excess of 4-(4-t-butyldimethylsilyloxymethyl)phenoxybutyric acid in methylene chloride to provide a resin-linked 4-(4-t- butyldimethylsilyloxymethyl)phenoxybutyr amide;

(b) treating the phenoxybutyramide with excess tetrabutylammonium fluoride in THF to provide a resin-linked p-hydroxymethylphenoxybutyramide; and (c) treating the p-hydroxymethylphenoxybutyramide with five to ten equivalents of phosphorus tribromide in methylene chloride.

-14-

In another particular embodiment, the invention relates to a process for preparing a compound of formula

HO- -(CH₂)₃ Me

\ / \ O Si — t-Bu

I Me

compπsing: (a) reacting ethyl 4-bromobutyrate with about one equivalent of 4- hydroxybenzyl alcohol in an inert solvent in the presence of at least one equivalent of cesium carbonate to provide ethyl 4-(p-hydroxymethyl)phenoxybutyrate; (b) reacting the ethyl 4-(p-hydroxymethyl)phenoxybutyrate with an excess of t- butyldimethylsilyl chloride in an inert solvent in the presence of at least one equivalent of imidazole to provide ethyl 4-(p-t- butyldimethylsilyloxymethyl)phenoxybutyrate; and

(c) hydrolyzing the ethyl 4-(p-t-butyldimethylsilyloxymethyl)phenoxybutyrate by treatment with an excess of lithium hydroxide in an aqueous solvent. This provides the desired compound, or a salt thereof, depending on whether or not the resulting lithium carboxylate is neutralized with acid. Additionally the lithium may be replaced by another cation, such as sodium or potassium.

For combinatorial synthesis, the solid phase-linker combination may be reacted with a phenol in the presence of a base. Alkali metal carbonates are simple to use and cheap, but other bases could be used, including organic bases. A preferred alkali metal carbonate is cesium carbonate, which is slurried with the resin and phenol in an inert solvent such as DMF.

When the combinatorial synthesis is complete, the linker can be cleaved from the resin by treatment with 50% trifluoroacetic acid in dichloromethane. -15-

Experimental

Ethyl-4-(p-hydroxymethyl)phenoxybutyrate(I) : 4-Hydroxybenzyl alcohol( 12.4g, 0.1 mole) in 100 mL DMF was treated at room temperature with ethyl 4- bromobutyrate (19.5g, 0.1 mole) followed by adding cesium carbonate (32.6g, 0. Imole). The reaction proceeded for 3 hours and was poured into 300 mL of ethyl acetate. The organic layer was washed with water (50mL x 2) and brine (50mL x 1), and dried over anhydrous sodium sulfate. About 4g clear oil was obtained after removal of solvent. This crude oil was quite pure, as shown by proton NMR, and was used for the next step without purification.

Ethyl 4-(p-t-butyldimethylsilyloxymethyl)phenoxybutyrate(2): A mixture of

I(2.38g, 0.01 mole) and t-butyldimethylsilyl chloride (1.66g, 0.011 mole) in 100 mL methylene chloride was treated at 0°C with imidazole(1.7g, 0.025 mole) and stirred at the same temperature for an hour. The white solid formed was filtered off, and the filtrate was passed through a short-packed silica column rinsed with a co- solvent of ethyl acetate-hexane(l :3). After removal of solvent, the crude product as a clear oil (3.4g) was used for the next step without further purification.

4-(p-t-Butyldimethylsilyloxymethyl)phenoxybutyric acid(3): Lithium hydroxide (2.4g, 0.1 mole) was added into 2 in 100 mL 1 : 1 : 1 THF-MeOH-H₂O, and the reaction was stirred at room temperature overnight. The reaction mixture was concentrated, diluted with water (50 mL), and washed twice with diethyl ether (30 mL x 2). The aqueous layer was acidified to pH 6 with IN HC1 at 0° and back- extracted with ethyl acetate (200 mL). The aqueous layer was further acidified with IN HC1 to pH~4 and back-extracted, while the combined organic layer was washed with brine and dried over sodium sulfate. After removal of solvent, 3 as white solid (lg) was obtained in a yield of 31% over three steps. -16-

Coupling of 3 onto N,N-bis-Fmoc lysine-loaded TentaGel®: Resin (1.7g, 0.61 mmol/g) was shaken for 30 min. in 50mL 20% piperidine-methylene chloride. Solvents were drawn out, and the resin was washed with methanol (50 mL, 2x), methylene chloride (50 mL, 3x), and suspended in methylene chloride (40 mL). 3_ (lg,3.09 mmol), HOBt(0.417g, 2.09mmol), and DIC (0.97 mL, 6.2 mmol) were added consecutively. The reaction was shaken at room temperature overnight. The resin was washed with DMF (50 mL, 2x), MeOH(50 mL, lx), CH₂Cl₂(50mL,3x), and THF(50mL, lx). Bromophenol blue test on the completely dried resin showed a colorless result. The resin was shaken with 1 M tetrabutylammonium fluoride in THF(40 mL) for 3 hours, and then washed with CH₂C1₂(50 mL,2x), MeOH(50 mL, 3x), and THF (50mL, lx). The resin was dried and stored in a freezer.

Formation of the p-Alkoxybenzyl bromide linker: The beads with p-alkoxybenzyl alcohol linker (1.2 g, 0.749 mmol) suspended in 30 mL CH₂C1₂ were treated with PBr₃(0.7 mL, 7.49 mmol) and shaken for 48 hours, washed with CH₂C1₂ (50 mL, 3x) and thoroughly dried under vacuum. The beads were stored at -10° C.

Attaching a ligand to the p-Alkoxybenzyl bromide linker on beads: The beads with p-alkoxybenzyl bromide linker (150 mg, 0.093 mmol) were washed with DMF(10 mL, lx) and then suspended in 5mL DMF. 5-Ethylthio-7-(m-hydroxy-p- methoxyphenyl)imidazopyrimidine (84mg, 0.279 mmol) and Cs₂CO₃ were added consecutively, and the reaction was shaken overnight. The beads were washed with DMF (10 mL, 2x), MeOH (lOmL, lx), CH₂C1₂(10 mL,2x), and THF(10 mL, lx).

Detaching the ligand from the acid cleavable linker on beads: The beads loaded with 5-ethylthio-7-(m-hydroxy-p-methoxyphenyl)imidazopyrimidine (12 mg, 5.575μmol) were stirred in lmL 50% TFA in CH₂C1₂ for 3 hours and then filtered. The filtrate was evaporated to dryness, leaving 1.4 mg off-white solid (yield: 84%).

Claims

-17- CLAIMS

1. A substrate for solid phase synthesis comprising a solid phase-linker combination of the formula:

O o

(CH₂)_n / -CH,X

wherein

f J — NH represents the residue of a solid support having a plurality of

amino functionalities;

X is bromo, chloro, mesylate or tosylate; and n is 3-20.

2. A substrate according to claim 1 wherein n is 3-5.

3. A substrate according to claim 1 wherein ( j — NH is chosen from

aminomethylated poly(styrene-co-divinylbenzene) and divinylbenzene-cross-linked, polyethyleneglycol-grafted polystyrene functionalized with amino groups.

4. A substrate according to claim 1 wherein X is bromo.

5. A chemical intermediate of the formula o R— L_(CH₂)_n — o- \ W / // ^~\ \ O S ϊ ,i— R 2²

R³ -18-

wherein n is 3-20;

R is chosen from OH, the residue of a solid support having a plurality of amino functionalities, and a residue of an activated ester; R¹ is lower alkyl or phenyl;

R² is lower alkyl or phenyl; and

R³ is lower alkyl, phenyl or lower alkoxy.

6. A chemical intermediate according to claim 5 wherein R is OH.

7. A chemical intermediate according to claim 5 wherein R is the residue of a solid phase substrate chosen from aminomethylated poly(styrene-co-divinylbenzene) and divinylbenzene-cross-linked, polyethyleneglycol-grafted polystyrene functionalized with amino groups.

8. A chemical intermediate according to claim 5 wherein R¹ and R² are methyl and R³ is t-butyl.

9. A chemical intermediate according to claim 5 wherein n is 3-5.

10. A process for preparing a substrate for solid phase synthesis of the formula:

-N- -(CH₂)„ O— v -CH₂Br

H

wherein

f V- NH represents the residue of a solid support having a plurality of

amino functionalities and n is 3-20, comprising -19-

(a) combining in a suitable solvent a condensing agent, a solid support having a plurality of amino functionalities, and a compound of formula

HO^l— (CH₂)_n O—

I ₂

Si — R²

A.

wherein R¹ is lower alkyl or phenyl;

R² is lower alkyl or phenyl; and R³ is lower alkyl, phenyl or lower alkoxy to provide a silylated precursor of a substrate for solid phase synthesis;

(b) treating said silylated precursor of a substrate for solid phase synthesis with a reagent capable of cleaving a silyl ether to provide a precursor of a substrate for solid phase synthesis; and

(c) treating said precursor of a substrate for solid phase synthesis with an excess of a brominating reagent in an inert solvent to provide a substrate for solid phase synthesis of the formula:

O CH₂Br

11. A process according to claim 10 wherein said solid support is chosen from aminomethylated poly(styrene-co-divinylbenzene) and divinylbenzene-cross-linked, polyethyleneglycol-grafted polystyrene functionalized with amino groups.

12. A process according to claim 10 wherein R¹ and R² are methyl, R³ is t-butyl and n is 3-5.

13. A process according to claim 12 wherein said reagent capable of cleaving a silyl ether is a tetraalkylammonium fluoride in an anhydrous solvent. -20-

14. A process according to claim 10 wherein said brominating reagent is phosphorus tribromide.

15. A process according to claim 10 for preparing a substrate for solid phase synthesis of the formula:

-N- "(CH₂)_n -CH₂Br

H

wherein n is 3-5 comprising (a) combining an excess of dialkylcarbodiimide, an excess of hydroxybenzotriazole, a solid support having a plurality of amino functionalities, and an excess of 4-(4-t-butyldimethylsilyloxymethyl)phenoxybutyric acid in methylene chloride to provide a resin-linked 4-(4-t- butyldimethylsilyloxymethyl)phenoxybutyr amide; (b) treating said phenoxybutyramide with excess tetrabutylammonium fluoride in THF to provide a resin-linked p-hydroxymethylphenoxybutyramide; and (c) treating said p-hydroxymethylphenoxybutyramide with five to ten equivalents of phosphorus tribromide in methylene chloride.

16. A process for preparing a substrate for solid phase synthesis of the formula:

O -CH₂Br

wherein

f j — NH represents the residue of a solid support having a plurality of

amino functionalities and n is 3-20, comprising

(a) combining in a suitable solvent a solid support having a plurality of amino functionalities, and a compound of formula -21-

o

-(CH₂)„

O. Si— R²

wherein R¹ is lower alkyl or phenyl; R² is lower alkyl or phenyl; R³ is lower alkyl, phenyl or lower alkoxy; and R⁴ is a residue displaceable by a primary amine to provide a silylated precursor of a substrate for solid phase synthesis;

O "(CH₂)_n CH₂Br

17. A process for preparing a compound of formula

HO- ^■(CH₂)„ ~\ ^~ I

^■Si-

R^Λ wherein R¹ is lower alkyl or phenyl;

R² is lower alkyl or phenyl; and

R³ is lower alkyl, phenyl or lower alkoxy comprising:

(a) reacting a lower alkyl ω-haloalkylcarboxylate with about one equivalent of 4-hydroxybenzyl alcohol in an inert solvent in the presence of at least one equivalent -22-

of an alkali metal carbonate to provide a lower alkyl ω-phenoxyalkylcarboxylate; (b) reacting said lower alkyl ω-phenoxyalkylcarboxylate with an excess of a silylating reagent in an inert solvent to provide a silylated lower alkyl ω- phenoxyalkylcarboxylate; and

(c) cleaving lower alkyl from said silylated lower alkyl ω- phenoxyalkylcarboxylate by treatment with an excess of an alkali metal hydroxide in an aqueous solvent to provide a compound of formula o

HO— "— (CH₂)_n O— (v / λ Λ R¹

O Si — R²

or salt thereof.

18. A process according to claim 17 wherein R¹ and R² are methyl, R³ is t-butyl and n is 3-5.

19. A process according to claim 17 wherein said lower alkyl ω- haloalkylcarboxylate is ethyl 4-bromobutyrate and said alkali metal carbonate is cesium carbonate.

20. A process according to claim 17 wherein said silylating reagent is a combination of t-butyldimethylsilyl chloride and imidazole.

21. A process according to claim 17 wherein said alkali metal hydroxide is lithium hydroxide.

22. A process for preparing a compound of formula

HO— L(CH₂)₃ O— (_\ ,) Me

\. 'J o Si— t-Bu

I Me comprising:

(a) reacting ethyl 4-bromobutyrate with about one equivalent of 4- -23-

hydroxybenzyl alcohol in an inert solvent in the presence of at least one equivalent of cesium carbonate to provide ethyl 4-(p-hydroxymethyl)phenoxybutyrate; (b) reacting said ethyl 4-(p-hydroxymethyl)phenoxybutyrate with an excess of t- butyldimethylsilyl chloride in an inert solvent in the presence of at least one equivalent of imidazole to provide ethyl 4-(p-t- butyldimethylsilyloxymethyl)phenoxybutyrate; and

(c) hydrolyzing said ethyl 4-(p-t-butyldimethylsilyloxymethyl)phenoxybutyrate by treatment with an excess of lithium hydroxide in an aqueous solvent to provide said compound of formula

HO— L(CH₂)₃ °'~ /) Me / o Si — t-Bu

I Me

or salt thereof.