Methods for preparing sulfonamide substituted alcohols and intermediates thereof

Processes for preparing amino alcohols or salts thereof and sulfonamide substituted alcohol compounds are provided. Desirably, the sulfonamide substituted alcohol compounds are heterocyclic sulfonamide trifluoroalkyl-substituted alcohol compounds or phenyl sulfonamide trifluoroalkyl-substituted alcohol compounds.

BACKGROUND OF THE INVENTION

This invention relates to inhibitors of beta amyloid production, which have utility in the treatment of Alzheimer's disease.

Alzheimer's Disease (AD) is the most common form of dementia (loss of memory) in the elderly. The main pathological lesions of AD found in the brain consist of extracellular deposits of beta amyloid protein in the form of plaques and angiopathy and intracellular neurofibrillary tangles of aggregated hyperphosphorylated tau protein. Recent evidence has revealed that elevated beta amyloid levels in the brain not only precede tau pathology but also correlate with cognitive decline. Further suggesting a causative role for beta amyloid in AD, recent studies have shown that aggregated beta amyloid is toxic to neurons in cell culture.

Heterocyclic- and phenyl-sulfonamide compounds, specifically fluoro- and trifluoroalkyl-containing heterocyclic sulfonamide compounds, have been shown to be useful for inhibiting β-amyloid production.

What is needed in the art are alternate processes for preparing sulfonamide compounds, which are useful for inhibiting β-amyloid production, and the intermediates thereof.

SUMMARY OF THE INVENTION

In one aspect, methods for preparing amino alcohols or salts thereof are provided.

In another aspect, methods for preparing sulfonamide substituted alcohols are provided.

Other aspects and advantages of the invention will be readily apparent from the following detailed description of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The methods describe herein provide routes to sulfonamide substituted alcohols. The methods also provide novel steps for preparing the intermediates thereof, including amino alcohols.

A. Methods of Preparing Amino Alcohols

A method for preparing an amino alcohol, or salt thereof, from an aminoester is described. See, Scheme 1, wherein R1, R2, R3and R4are defined below.

In one embodiment, the amino alcohol is of the structure:

The term “protecting group” as used herein refers to a group that protects an amino functional group. Desirably, the protecting group may be removed by deprotection under conditions known to those of skill in the art. A variety of protecting groups are known in the art and include those set forth in Green et al., “Protective Groups in Organic Synthesis”, 3rd Edition, John Wiley & Sons Inc, June, 1999 and US Patent Publication No. 2004/0198778, which is hereby incorporated by reference herein. In one embodiment, the protecting group is a chiral protecting group. In another embodiment, the protecting group is an optionally substituted alkyl, cycloalkyl, or carbonyl. In a further embodiment, the protecting group is 1-methylbenzyl, benzyl, t-butyloxycarbonyl (BOC), or acetyl, among others. In yet another embodiment, the protecting group is 1-methylbenzyl.

In a further embodiment, the amino alcohol is of the following structure:

wherein, R3is selected from among hydrogen, lower alkyl and substituted lower alkyl; R4is selected from among (CF3)nalkyl, (CF3)n(substituted alkyl), (CF3)nalkylphenyl, (CF3)nalkyl(substituted phenyl), and (F)ncycloalkyl; and n is 1 to 3.

In one embodiment, the amino alcohol is:

In a further embodiment, the amino alcohol is (2S)-4,4,4-trifluoro-2-{[(1R)-1-phenylethyl]amino}-3-(trifluoromethyl)butan-1-ol:

Alternatively, an amino alcohol salt of the following structure can be prepared from the aminoesters noted above.

wherein, R3is selected from among hydrogen, lower alkyl and substituted lower alkyl; R4is selected from among (CF3)nalkyl, (CF3)n(substituted alkyl), (CF3)nalkylphenyl, (CF3)nalkyl(substituted phenyl), and (F)ncycloalkyl; and n is 1 to 3.

In another embodiment, the amino alcohol salt is:

In a further embodiment, the amino alcohol salt is:

The amino alcohols are prepared by reducing the aminoester. The reduction is performed by adding the aminoester to a reducing agent. The term “reducing agent” as used herein refers to a compound or complex that converts the ester functional group of the aminoester to an alcohol functional group. One of skill in the art would readily be able to select a suitable reducing agent for the reduction. Suitable reducing agents include hydride reducing agents including, without limitation, sodium borohydride (NaBH4), lithium aluminum hydride (LAH), lithium borohydride, diisobutylaluminum hydride (DIBAL-H), sodium bis-methoxy ethoxy aluminum hydride, sodium bis(2-methoxyethoxy)aluminum hydride (red-Al), k-selectride, among others, including those set forth in “Comprehensive Organic Transformations”, R. C. Larock, VCH Publishers, Inc., New York, N.Y., 1989, which is hereby incorporated by reference herein. Desirably, the reducing agent is DIBAL-H.

The reduction is typically performed using a non-reactive solvent. The term “non-reactive solvent” as used herein refers to a solvent that does not react with any of the reagents utilized during the reduction. Desirably, the non-reactive solvent utilized during the reduction includes toluene, tetrahydrofuran (THF), hexanes, heptane, dichloromethane, cyclohexane, among others.

The inventors have found that when the aminoester is added to the reducing agent, i.e., DIBAL-H, the yield of amino alcohol is higher than if the reducing agent is added to the aminoester. Typically, the amino alcohol is prepared in a yield of greater than about 90%, greater than about 91%, greater than about 92%, greater than about 93%, greater than about 94%, or greater than about 95%. In one embodiment, the amino alcohol is prepared in a yield of about 90 to about 95%.

The temperature utilized during the reduction is higher than about −60° C. In one embodiment, the reduction to the amino alcohol is performed at about −60° to about −10° C. In another embodiment, the reduction is performed at about −20 to about −10° C. In a further embodiment, the reduction is performed at about −8 to −11° C. In yet another embodiment, the reduction is performed at about −10° C.

The reduction to the amino alcohol is later quenched using a protic solvent. By the term “protic solvent” is meant a solvent that contains a hydrogen source (H+) that can be released in a solution. Typically, the hydrogen source is attached to an oxygen atom of the protic solvent. In one embodiment, the protic solvent contains a hydroxyl group. In another embodiment, the protic solvent is an alcohol, such as ethanol. In a further embodiment, the protic solvent is a protic acid. The term “protic acid” as used herein includes, without limitation, strong and weak acids such as hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, trihaloacetic acid, hydrogen bromide, maleic acids, sulfonic acids, propionic acids, tartaric acids, lactic acids, camphoric acids, aspartic acids, citronellic acids, BCl3, ethanolic acids, hydrogen sulfide, methanesulfonic acid, trifluoroacetic acid, among others. In yet another embodiment, the protic solvent is a mixture of solvents that contain hydrogen atoms that can be released in solution.

A number of aminoesters can be reduced and can be determined by one of skill in the art utilizing techniques and knowledge in the art and in the instant specification. Desirably, the aminoester contains one or more chiral carbon centers. More desirably, the aminoester is a protected aminoester. Most desirably, the aminoester is an N-protected aminoester. In one embodiment, the aminoester is of the following structure:

wherein, R1is alkyl or benzyl; R2is a protecting group; R3is selected from among hydrogen, lower alkyl and substituted lower alkyl; R4is selected from among (CF3)nalkyl, (CF3)n(substituted alkyl), (CF3)nalkylphenyl, (CF3)nalkyl(substituted phenyl), and (F)ncycloalkyl; and n is 1 to 3.

In another embodiment, the aminoester is of the following structure, wherein R1, R3, and R4are defined above:

In a further embodiment, the aminoester is of the following structure, wherein R1, R3, and R4are defined above:

In still another embodiment, the aminoester is:

In yet a further embodiment, the aminoester is:

In one example, a method is provided for preparing an amino alcohol, or salt thereof, from an aminoester including reducing the aminoester by adding the aminoester to diisobutylaluminum hydride at about −60° to about −10° C.

In another example, a method is provided for preparing an amino alcohol of the structure:

wherein, an aminoester of the following structure is reduced by adding the aminoester to diisobutylaluminum hydride at about −60° to about −10° C.

B. Methods for Preparing Sulfonamide Substituted Alcohols

Also provided are methods for preparing sulfonamide substituted alcohols. In one embodiment, the sulfonamide substituted alcohol is substituted with one or more trifluoroalkyl groups. In another embodiment, the sulfonamide substituted alcohol is a heterocyclic sulfonamide substituted alcohol or phenylsulfonamide substituted alcohol. See, Scheme 2.

In one embodiment, the sulfonamide substituted alcohol is of the structure:

wherein, R3is selected from among H, lower alkyl and substituted lower alkyl; R4is selected from among (CF3)nalkyl, (CF3)n(substituted alkyl), (CF3)nalkyl phenyl, (CF3)nalkyl(substituted phenyl), and (F)ncycloalkyl; n is 1 to 3; R5is selected from among H, halogen, CF3, diene fused to Y when Y is C, and substituted diene fused to Y when Y is C; W, Y and Z are independently selected from among C, CR6and N, wherein at least one of W, Y or Z is C; X is selected from among O, S, SO2, and NR7; R6is selected from among H, halogen, C1to C6alkyl, and substituted C1to C6alkyl; and R7is selected from among H, C1to C6alkyl, and C3to C8cycloalkyl.

The point of attachment of the W-X-Y-Z-C heterocyclic ring to the SO2group is not a limitation. The ring may be attached to the SO2group through a carbon-atom or nitrogen-atom.

In one embodiment, the compounds prepared as described herein are thiophenesulfonamides, more desirably 5-halo thiophenesulfonamides, and most desirably 5-halo thiophene sulfonamides with β-branches in the side chain of a primary alcohol.

In a further embodiment, the substituted sulfonamide substituted alcohol is:

In another embodiment, the compounds prepared are furansulfonamides. Thus, the compounds have a structure in which X is O. In one desirable embodiment, the furansulfonamides are characterized by β-branches in the side chain of a primary alcohol.

In still a further embodiment, the compounds described herein are pyrazole sulfonamides. Thus, the compound has a structure in which X is NR7, W is N and Z and Y are C or CR6, with the proviso that at least one of Y or Z must be C.

In another embodiment, the sulfonamide trifluoroalkyl substituted alcohol is 5-Chloro-N-[(1S)-3,3,3-trifluoro-1-(hydroxymethyl)-2-(trifluoromethyl)propyl]thiophene-2-sulfonamide or 4-Chloro-N-[(1S)-3,3,3-trifluoro-1-(hydroxymethyl)-2-(trifluoromethyl)propyl]benzenesulfonamide.

In one example, R3is H, R4is (CF3)2CH, desirably of S-stereochemistry, R5is halogen, W is C, X is S, Y is CH, and Z is CH with the sulfonamide attached to C-2 of the thiophene ring.

In another example, R3is H, R4is (CH2CF3)2CH, R5is halogen, W is C, X is S, Y is CH, and Z is CH with the sulfonamide attached to C-2 of the thiophene ring.

In yet a further example, R3is H, R4is (F)2cycloalkyl, R5is halogen, W is C, X is S, Y is CH, Z is CH with the sulfonamide attached to C-2 of the thiophene ring.

In still another example, the substituted sulfonamide substituted alcohol is:

In yet a further example, the substituted sulfonamide substituted alcohol is:

In another embodiment, the sulfonamide substituted alcohol is of the structure:

In one example, the substituted sulfonamide substituted alcohol is:

The methods thereby include isolating one diastereomer of an N-protected aminoester by reacting a diastereomeric mixture of N-protected aminoesters with a protic acid to form the corresponding N-protected aminoester salt. The desired diastereomer of the aminoester salt is typically isolated by treating the diastereomeric mixture with a protic acid to form salts of the N-protected aminoesters. The term “protic acid” as used herein refers to any acid that donates a hydrogen atom (H+). A variety of protic acids can be utilized to convert the amino alcohols to the corresponding salt and include, without limitation, hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, among others. The desired single diastereomeric N-protected aminoester salt precipitates from the solution and is then isolated using techniques in the art such as filtration, decanting, among others. Desirably, the single diastereomeric N-protected aminoester salt is isolated using filtration. The N-protected aminoester salt can then be utilized without further purification or can be purified using techniques known to those of skill in the art.

In one embodiment, the N-protected aminoester salt is of the structure:

wherein, R1is alkyl or benzyl; R3is selected from among hydrogen, lower alkyl and substituted lower alkyl; R4is selected from among (CF3)nalkyl, (CF3)n(substituted alkyl), (CF3)nalkylphenyl, (CF3)nalkyl(substituted phenyl), and (F)ncycloalkyl; and n is 1 to 3.

In another embodiment, the N-protected aminoester salt is:

The N-protected aminoester salt is then treated with a base to form the corresponding N-protected aminoester of the single diastereomer. The term based as used herein refers to a chemical compound that is capable of accepting protons. Therefore, the term base includes, without limitation, hydroxides such as potassium, lithium or sodium hydroxide, alkoxides, hydrides, amines, among others and including those described in US Patent Application Publication No. US-2005/0272932, which is hereby incorporated by reference.

The N-protected aminoester is then reduced to the N-protected amino alcohol by adding the N-protected aminoester to DIBAL-H as described above. The reduction is then quenched with a protic solvent as described above to form the N-protected amino alcohol.

The N-protected amino alcohol is then converted to the corresponding N-protected amino alcohol salt by reacting the N-protected amino alcohol with a protic acid as described above.

The N-protected amino alcohol salt is then hydrogenated to form the unprotected amino alcohol salt. One of skill in the art would readily be able to select a suitable hydrogenating agent for use in the hydrogenation. Desirably, hydrogen is utilized in the presence of a catalyst. Catalysts that are useful in the hydrogenation include those recited in Larock et al. cited above, which is hereby incorporated by reference. Desirably, the hydrogenation is performed using Pd/C.

The unprotected amino alcohol salt is then sulfonylated using a sulfonyl chloride to form a sulfonamide substituted alcohol. In one embodiment, the sulfonyl chloride is of the structure:

wherein, R5is selected from among H, halogen, and CF3; W, Y and Z are independently selected from among C, CR6and N, wherein at least one of W, Y or Z is C; X is selected from among O, S, SO2, and NR7; R6is selected from among H, halogen, C1to C6alkyl, and substituted C1to C6alkyl; R7is selected from among H, C1to C6alkyl, and C3to C8cycloalkyl.

In another embodiment, the sulfonyl chloride is:

In still a further embodiment, the sulfonyl chloride is of the structure:

Desirably, the sulfonylation is performed in the absence of protection and deprotection steps. More desirably, the sulfonylation is performed in the absence of any silylation or desilylation steps as described in US Patent Application Publication No. US-2004/0198778 A1, which is hereby incorporated by reference.

Typically, the sulfonylation is performed using a base/solvent system including 4-methyl morpholine/isopropyl acetate, Hünig's base/tetrahydrofuran, 4-methyl morpholine/acetonitrile, 4-methyl morpholine/propionitrile, and 4-methyl morpholine/toluene using the procedure described in U.S. Provisional Patent Application No. 60/774, 300, which is hereby incorporated by reference.

The sulfonamide substituted alcohol is then optionally purified using techniques known to those of skill in the art. Desirably, the purification is performed in the absence of chromatography, including the use of silica gel chromatography.

The compounds may contain one or more asymmetric carbon atoms and some of the compounds may contain one or more asymmetric (chiral) centers and may thus give rise to optical isomers and diastereomers. While shown without respect to stereochemistry, when the compounds contain one or more chiral centers, at least the chiral center of the β-amino alcohol is of S-stereochemistry. Desirably, the chiral centers include the carbon atom to which the N-atom, R3, and R4are attached (the α-carbon atom). More desirably, the α-carbon atom is chiral. Most desirably, the α-carbon atom is chiral and is of S-stereochemistry. Thus, the compounds include such optical isomers and diastereomers; as well as the racemic and resolved, enantiomerically pure stereoisomers; as well as other mixtures of the R and S stereoisomers, and pharmaceutically acceptable salts, hydrates, and prodrugs thereof.

The term “alkyl” is used herein to refer to both straight- and branched-chain saturated aliphatic hydrocarbon groups having one to ten carbon atoms (e.g., C1, C2, C3, C4, C5, C6, C7, C8, C9, or C10), such as one to eight carbon atoms (e.g., C1, C2, C3, C4, C5, C6, C7, or C8), one to six carbon atoms (e.g., C1, C2, C3, C4, C5, or C6), or one to four carbon atoms (e.g., C1, C2, C3, or C4). The term “lower alkyl” refers to straight- and branched-chain saturated aliphatic hydrocarbon groups having one to six carbon atoms (e.g., C1, C2, C3, C4, C5, or C6), desirably one to four carbon atoms (e.g., C1, C2, C3, or C4). The term “alkenyl” refers to both straight- and branched-chain alkyl groups with at least one carbon-carbon double bond and two to eight carbon atoms (e.g., C2, C3, C4, C5, C6, C7, or C8), two to six carbon atoms (e.g., C2, C3, C4, C5, or C6), or two to four carbon atoms (e.g., C2, C3, or C4). The term “alkynyl” refers to both straight- and branched-chain alkyl groups with at least one carbon-carbon triple bond and two to eight carbon atoms (e.g., C2, C3, C4, C5, C6, C7, or C8), two to six carbon atoms (e.g., C2, C3, C4, C5, or C6), or two to four carbon atoms (e.g., C2, C3, or C4).

The terms “substituted alkyl”, “substituted alkenyl”, and “substituted alkynyl” refer to alkyl, alkenyl, and alkynyl groups as just described having from one to three substituents including halogen, CN, OH, NO2, amino, aryl, substituted aryl, heterocyclic, substituted heterocyclic, heteroaryl, substituted heteroaryl, alkoxy, substituted alkoxy, aryloxy, substituted aryloxy, alkylcarbonyl, alkylcarboxy, alkylamino, and arylthio. These substituents may be attached to any carbon of an alkyl, alkenyl, or alkynyl group provided that the attachment constitutes a stable chemical moiety.

The term “cycloalkyl” is used herein to describe a carbon-based saturated ring having more than 3 carbon-atoms and which forms a stable ring. The term cycloalkyl can include groups where two or more cycloalkyl groups have been fused to form a stable multicyclic ring. Desirably, cycloalkyl refers to a ring having about 4 to about 9 carbon atoms, and more desirably about 6 carbon atoms.

The term “aryl” is used herein to refer to a carbocyclic aromatic system, which may be a single ring, or multiple aromatic rings fused or linked together as such that at least one part of the fused or linked rings forms the conjugated aromatic system. The aryl groups include, but are not limited to, phenyl, naphthyl, biphenyl, anthryl, tetrahydronaphthyl, phenanthryl, and indane. Desirably, aryl refers to a carbocyclic aromatic system having about 6 to about 14 carbon atoms.

The term “heterocycle” or “heterocyclic” as used herein can be used interchangeably to refer to a stable, saturated or partially unsaturated 3- to 9-membered monocyclic or multicyclic heterocyclic ring. The heterocyclic ring has in its backbone carbon atoms and one or more heteroatoms including nitrogen, oxygen, and sulfur atoms. In one embodiment, the heterocyclic ring contains 1 to about 4 heteroatoms in the backbone of the ring. When the heterocyclic ring contains nitrogen or sulfur atoms in the backbone of the ring, the nitrogen or sulfur atoms can be oxidized. The term “heterocycle” or “heterocyclic” also refers to multicyclic rings in which a heterocyclic ring is fused to an aryl ring of about 6 to about 14 carbon atoms. The heterocyclic ring can be attached to the aryl ring through a heteroatom or carbon atom provided the resultant heterocyclic ring structure is chemically stable. In one embodiment, the heterocyclic ring includes multicyclic systems having 1 to 5 rings.

The term “heteroaryl” as used herein refers to a stable, aromatic 5- to 14-membered monocyclic or multicyclic heteroatom-containing ring. The heteroaryl ring has in its backbone carbon atoms and one or more heteroatoms including nitrogen, oxygen, and sulfur atoms. In one embodiment, the heteroaryl ring contains 1 to about 4 heteroatoms in the backbone of the ring. When the heteroaryl ring contains nitrogen or sulfur atoms in the backbone of the ring, the nitrogen or sulfur atoms can be oxidized. The term “heteroaryl” also refers to multicyclic rings in which a heteroaryl ring is fused to an aryl ring. The heteroaryl ring can be attached to the aryl ring through a heteroatom or carbon atom provided the resultant heterocyclic ring structure is chemically stable. In one embodiment, the heteroaryl ring includes multicyclic systems having 1 to 5 rings.

The term “alkoxy” is used herein to refer to the OR group, where R is alkyl or substituted alkyl. The term “lower alkoxy” refers alkoxy groups having one to six carbon atoms.

The term “aryloxy” is used herein to refer to the OR group, where R is aryl or substituted aryl.

The term “arylthio” is used herein to refer to the SR group, where R is aryl or substituted aryl.

The term “alkylcarbonyl” is used herein to refer to the RCO group, where R is alkyl or substituted alkyl.

The term “alkylcarboxy” is used herein to refer to the COOR group, where R is alkyl or substituted alkyl.

The term “aminoalkyl” refers to both secondary and tertiary amines wherein the alkyl or substituted alkyl groups, containing one to eight carbon atoms, may be either the same or different, and the point of attachment is on the nitrogen atom.

The term “halogen” refers to Cl, Br, F, or I.

Physiologically acceptable alkali salts and alkaline earth metal salts can include, without limitation, sodium, potassium, calcium and magnesium salts in the form of esters, and carbamates.

These salts, as well as other compounds, can be in the form of esters, carbamates and other conventional “pro-drug” forms, which, when administered in such form, convert to the active moiety in vivo. In one embodiment, the prodrugs are esters. In another embodiment, the prodrugs are carbamates. See, e.g., B. Testa and J. Caldwell, “Prodrugs Revisited: The “Ad Hoc” Approach as a Complement to Ligand Design”, Medicinal Research Reviews, 16(3):233-241, ed., John Wiley & Sons (1996).

In one example, a method is provided for preparing a sulfonamide substituted alcohol, including isolating one diastereomer of a N-protected aminoester by reacting a mixture of diastereomers of a N-protected aminoester with a protic acid to form a N-protected aminoester salt; neutralizing the N-protected aminoester salt with a base to form a N-protected aminoester; reducing the N-protected aminoester by adding the N-protected aminoester to a reducing agent at −60° C. to about −10° C.; quenching the reduction with a protic solvent; reacting the N-protected amino alcohol with a protic acid to form a N-protected amino alcohol salt; hydrogenating the N-protected amino alcohol salt to form an unprotected amino alcohol salt; and sulfonylating the unprotected amino alcohol with a sulfonyl chloride in the presence of a base/solvent system. See, Scheme 3.

In another example, a method is provided for preparing a sulfonamide substituted alcohol, including isolating one diastereomer of a N-protected aminoester by reacting a mixture of diastereomers of a N-protected aminoester with a protic acid to form a N-protected aminoester salt; neutralizing the N-protected aminoester salt with a base to form a N-protected aminoester; reducing the N-protected aminoester by adding the N-protected aminoester to diisobutylaluminum hydride at −60° C. to about −10° C.; quenching the reduction with a protic solvent; reacting the N-protected amino alcohol with a protic acid to form a N-protected amino alcohol salt; hydrogenating the N-protected amino alcohol salt to form an unprotected amino alcohol salt; and sulfonylating the unprotected amino alcohol with a sulfonyl chloride in the presence of a base/solvent system.

In a further example, a method is provided for preparing a sulfonamide substituted alcohol, including isolating one diastereomer of a N-protected aminoester by reacting a mixture of diastereomers of a N-protected aminoester with a protic acid to form a N-protected aminoester salt; neutralizing the N-protected aminoester salt with a base to form a N-protected aminoester; reducing the N-protected aminoester by adding the N-protected aminoester to diisobutylaluminum hydride at −60° C. to about −10° C.; quenching the reduction with a protic solvent; reacting the N-protected amino alcohol with a protic acid to form a N-protected amino alcohol salt; hydrogenating the N-protected amino alcohol salt to form an unprotected amino alcohol salt; and sulfonylating the unprotected amino alcohol with a sulfonyl chloride in the presence of a base/solvent system selected from among 4-methyl morpholine/isopropyl acetate, Hünig's base/tetrahydrofuran, 4-methyl morpholine/acetonitrile, 4-methyl morpholine/propionitrile, and 4-methyl morpholine/toluene.

In yet another example, a method is provided for preparing a sulfonamide substituted alcohol, including isolating one diastereomer of a N-protected aminoester by reacting a mixture of diastereomers of a N-protected aminoester with a protic acid to form a N-protected aminoester salt; neutralizing the N-protected aminoester salt with a base to form a N-protected aminoester; reducing the N-protected aminoester by adding the N-protected aminoester to diisobutylaluminum hydride at −60° C. to about −10° C.; quenching the reduction with a protic solvent; reacting the N-protected amino alcohol with a protic acid to form a N-protected amino alcohol salt; hydrogenating the N-protected amino alcohol salt to form an unprotected amino alcohol salt; and sulfonylating the unprotected amino alcohol with a sulfonyl chloride in the presence of a base/solvent system, wherein the sulfonylation is performed in the absence of protection and deprotection steps.

In still a further example, a method is provided for preparing a sulfonamide substituted alcohol, including isolating one diastereomer of a N-protected aminoester by reacting a mixture of diastereomers of a N-protected aminoester with a protic acid to form a N-protected aminoester salt; neutralizing the N-protected aminoester salt with a base to form a N-protected aminoester; reducing the N-protected aminoester by adding the N-protected aminoester to diisobutylaluminum hydride at −60° C. to about −10° C.; quenching the reduction with a protic solvent; reacting the N-protected amino alcohol with a protic acid to form a N-protected amino alcohol salt; hydrogenating the N-protected amino alcohol salt to form an unprotected amino alcohol salt; sulfonylating the unprotected amino alcohol with a sulfonyl chloride in the presence of a base/solvent system; and purifying the sulfonamide substituted alcohol, wherein the purification is performed in the absence of silica gel.

The following examples are illustrative only and are not intended to be a limitation on the present invention.

EXAMPLES

Preparation of 4,4,4-Trifluoro-2-(1-Phenethylamino)-3-Trifluoromethylbutan-1 -ol

A solution of 50% NaOH (24 g, 0.302 mol) in water (80 mL) was added to a suspension of ethyl 4,4,4,4′,4′,4′-hexafluoro-N-[(1R)-1-phenylethyl]-L-valinate hydrochloride salt aminoester (100 g, 0.254 mol) in water (278 mL) and toluene (1.01 L). The mixture was stirred for 30 minutes and then the two phases were separated. The toluene layer was washed with water (2×195 mL) and the water was removed by azeotroping. The toluene solution was distilled under atmospheric pressure until the vapor temperature reached about 108-110° C., whereby about 600 mL of toluene remained in the flask.

A solution of DIBAL-H in toluene (1.5 N, 518 mL, 0.78 mol) was cooled to −10° C. and then the aminoester toluene solution (about 600 mL) was added over about 90 minutes while keeping the reaction mixture at about −8 to −11° C. The mixture was then stirred for about 10 minutes. EtOH (29 mL, 0.5 mol) was then added over 10 minutes, while keeping the reaction temperature below 25° C.

A solution of concentrated HCl (93 g) in water (130 mL) was heated to 35-40° C. The reaction mixture was then added to this heated HCl solution over 60 to 90 minutes while maintaining the temperature below 45° C. This mixture was then stirred at 40-45° C. for 30 minutes. The two layers were separated and the organic layer was washed with 15% NaCl (700 mL). The organic layer solution was then cooled to −5° C. and then concentrated HCl (32 g, 0.33 mol) was added over 15 minutes. This mixture was then stirred for 6 hours. The salt product from the previous step was then isolated by filtration, washed with toluene (2×200 mL) and dried in a vacuum oven to give 81 g (90%) of the final product as an off-white solid. 98.9 area % HPLC purity, 98.5% strength.

Preparation of 5-Chloro-N-[(1S)-3,3,3-trifluoro-1-(hydroxymethyl)-2-(trifluoro-methyl)propyl]thiophene-2-sulfonamide

4-methyl morpholine (2.7 mL, 24.6 mmol) was added to a suspension of (2S)-2-amino-4,4,4-tri-fluoro-3-(trifluoromethyl)butan-1-ol (2 g, 8.1 mmol) in isopropyl acetate (10 mL). The mixture was stirred at about 20-25° C. for about 5-10 minutes and then 5-chlorothiophene-2-sulfonyl chloride (2.0 g, 9.2 mmol) was added. The reaction mixture was stirred at 20-25° C. for 6-18 hours. Water (10 mL) was then added to the reaction mixture, whereby the solids dissolved. The two layers were then separated and the organic layer was washed with a solution of 10% NaHCO3(10 mL) and 10% NaCl (10 mL). Heptane (10 mL) was added to the isopropyl acetate layer (about 10 mL). The mixture was then distilled down to about half of its original volume under atmospheric distillation. While the solution remained at about 80-90° C., heptane (10 mL) was added over 5-10 minutes, during which time solids formed. After the addition of heptane, the mixture was cooled to 20-25° C., stirred for about 1-2 hours, and then further cooled to about 5-10° C. for 1 hour. The solid was then collected by filtration, washed with heptane (5 mL), and oven-dried to give 2.15 g (67%) of the product as an off-white solid. 98 area% HPLC purity and >99% chiral purity by HPLC.

All publications cited in this specification are incorporated herein by reference. While the invention has been described with reference to particular embodiments, it will be appreciated that modifications can be made without departing from the spirit of the invention. Such modifications are intended to fall within the scope of the appended claims.