Processes and intermediates for preparing benzyl epoxides

The invention provides processes for preparing benzyl substituted epoxides useful in the preparation of biologically active compounds.

International PublicationsWO02/02512 and WO98/33795 disclose various hydroxyethylamines useful in treating Alzheimer's disease. A common intermediate in most of the products of WO02/02512 is an N-protected epoxide. As a result, there exists a need for processes and intermediates that efficiently produce N-protected epoxides.

In a broad aspect, the invention provides a process for preparing a compound of formula (XX) wherein R_c is 3-methoxybenzyl or 3-iodobenzyl; and comprising

1. (a) reducing a ketone of formula III where PROT is a nitrogen protecting group; and R₂ is chloro to generate an alcohol of formula IV and
2. (b) treating the alcohol of formula IV with a base to generate an epoxide.

In a further aspect of the invention, the process further comprises contacting the epoxide with an amine of formula R_cNH₂ to yield a protected amine of formula VII.

In an additional aspect of the invention, the process further comprises forming a deprotected amine of formula VIII and forming an amide using the amine of formula VIII and a compound of the formula wherein Z is OH, Cl, or imidazolyl.

The invention provides a process of preparing a compound of formula (XX), further comprising contacting the epoxide with an amine of formula R_cNH₂ to yield a protected amine of formula VII.

In another aspect, the invention provides a process of preparing a compound of formula (XX), further comprising deprotecting the protected amine of formula (VII) to generate a an amine or its acid addition salt of formula (VIII).

In another aspect, the invention provides a process of preparing a compound of formula (XX), further comprising the deprotected amine of formula VIII and forming an amide using the amine and a compound of the formula wherein Z is OH, Cl, or imidazolyl.

In a more preferred embodiment, Z is OH. In an equally preferred embodiment, Z is Cl. In yet another equally preferred embodiment, Z is imidazolyl.

A particularly preferred group of compounds represented by Formula III are those of Formula III-B, wherein R₂ is chloro and PROT is a nitrogen protecting group.

Preferred PROT groups are t-butoxycarbonyl, benzyloxycarbonyl, formyl, trityl, phthalimido, trichloroacetyl, chloroacetyl, bromoacetyl; iodoacetyl, 4-phenylbenzyloxycarbonyl, 2-methylbenzyloxycarbonyl, 4-ethoxybenzyloxycarbonyl, 4-fluorobenzyloxycarbonyl, 4-chlorobenzyloxycarbonyl, 3-chlorobenzyloxycarbonyl, 2-chlorobenzyloxycarbonyl, 2,4-dichlorobenzyloxycarbonyl, 4-bromobenzyloxycarbonyl, 3-bromobenzyloxycarbonyl, 4-nitrobenzyloxycarbonyl, 4-cyanobenzyloxycarbonyl, 2-(4-xenyl)isopropoxycarbonyl, 1,1-diphenyleth-1-yloxycarbonyl, 1,1-diphenylprop-1-yloxycarbonyl, 2-phenylprop-2-yloxycarbonyl, 2-(p-toluyl)prop-2-yloxycarbonyl, cyclopentanyloxycarbonyl, 1-methylcycoopentanyloxycarbonyl, cyclohexanyloxycarbonyl, 1-methylcyclohexanyloxycabonyl, 2-methylcyclohexanyloxycarbonyl, 2-(4-toluylsulfonyl)ethoxycarbonyl, 2-(methylsulfonyl)ethoxycarbonyl, 2-(triphenylphosphino)ethoxycarbonyl, (trimethylsilylmethyl)prop-1-enyloxycarbonyl, 5-benzisoxalylmethoxycarbonyl, 4-acetoxybenzyloxycarbonyl, 2,2,2-trichloroethoxycarbonyl, 2-ethynyl-2-propoxycarbonyl, cyclopropylmethoxycarbonyl, 4-(decyloxyl)benzyloxycarbonyl, isobornyloxycarbonyl, 1-piperidyloxycarbonyl, 9-fluoroenylmethyl carbonate, -CH-CH=CH₂ and (-N=)CH-phenyl.

It is preferred that the nitrogen protecting group (PROT) be t-butoxycarbonyl (BOC) or benzyloxycarbonyl (CBZ), it is more preferred that PROT be t-butoxycarbonyl. One skilled in the art will understand the preferred methods of introducing a t-butoxycarbonyl or benzyloxycarbonyl groups and may additionally consult T. W. Green and P. G. M. Wuts in "Protective Groups in Organic Chemistry, 3rd edition" John Wiley & Sons, Inc. New York, N.Y., 1999 for guidance. (Reference) Schemes 1-7 generally represent the processes of the invention; while these schemes employ various preferred compounds of the invention as intermediates and starting materials, it is to be understood that the processes are also applicable to compounds not having the specific stereochemistry or substituent patterns depicted in the schemes. In summary:

• Scheme 1 generally sets forth the process for the preparation of the N-protected epoxide V from known amino acid (0). Epoxides of Formula V are useful as intermediates in the production of biologically active compounds, e.g., pharmaceuticals for the treatment of Alzheimer's Disease.
• Scheme 2 discloses a process for the transformation of an epoxide V to the desired compounds of Formula X.
• Reference Scheme 3 discloses an alternative process for the conversion of the protected amino acid (I) to the corresponding ketone (III).
• Reference Scheme 4 discloses an alternative process to prepare the ester (II).
• Reference Scheme 5 discloses a process to change the protecting group for the ester (II).
• Reference Scheme 6 discloses a process to prepare the unprotected alcohol (IV-unprotected) and the unprotected epoxide (V-unprotected).
• Scheme 7 discloses a process for the transformation of an epoxide V-1 to the desired compounds of Formula X-1.

Representative examples of methods for preparing compounds of the invention are set forth below.

The epoxides of formula V have two chiral centers; thus, compounds of Formula V can exist as any of four stereoisomers, i.e., two pairs of diastereomers. While biologically active end products result from all stereoisomers, the (S,S) configuration is particularly preferred. One of these chiral centers in the epoxide (V) is derived from the starting amino acid (0). Therefore, it is preferred to start with the amino acid (0) containing the desired enantiomeric center rather than to start with a mixture and have to perform a resolution to obtain the desired (S)-enantiomer of the amino acid (0).

SCHEME 1 depicts the conversion of amino acid (0) to N-protected amino epoxide (V). Protection of the free amino group of the preferably (S)-amino acid (0) with a nitrogen protecting group (PROT) yields the protected amino acid (I) having the same stereochemistry. Nitrogen protecting groups are well known to those skilled in the art, see for example, "Nitrogen Protecting Groups in Organic Synthesis", John Wiley and sons, New York, N.Y., 1981, Chapter 7; "Nitrogen Protecting Groups in Organic Chemistry", Plenum Press, New York, N.Y., 1973, Chapter 2. See also, T. W. Green and P. G. M. Wuts in "Protective Groups in Organic Chemistry, 3rd edition" John Wiley & Sons, Inc. New York, N.Y., 1999. When the nitrogen protecting group is no longer needed, it may be removed. Suitable methods are known to those skilled in the art. The reader's attention is again directed to the references mentioned above.

The protected amino acid (I) (preferably of (S) stereochemistry) is then converted to the corresponding protected ester (II) (retaining the preferred (S) stereochemistry). This conversion can be accomplished in a variety of ways.

When R₁ is (a) C₁-C₄ alkyl optionally substituted with one -Cl, (b) -CH₂-CH=CH₂, or (c) phenyl optionally substituted with one nitro, halogen, or cyano conversion of I to II comprises:

1. (1) esterifying a protected amino acid of the formula I with an alkylating agent in the presence of a base. Suitable alkylating agents include
   1. (a) those represented by the formula X₄-C₁-C₄ alkyl optionally substituted with one -Cl where X₄ is iodo, bromo, chloro, -O-tosylate, -O-mesylate or -O-triflate;
   2. (b) dimethylsulfate
   3. (c) X₄-CH₂-CH=CH₂, where X₄ is as defined above
   4. (d) a benzyl substituted on the methyl group with X₄ where X₄ is defined as above and where the phenyl ring is optionally substituted with nitro, halogen, or cyano.

While a variety of bases are suitable for this esterification, the base is preferably hydroxide, carbonate, bicarbonate, LDA, n-(C₁-C₈ alkyl)lithium, LiHMDS, NaHMDS or KHMDS. More preferably, the base is hydroxide, carbonate or bicarbonate. An even more preferred base is carbonate.

Preferred alkylating agents are dimethylsulfate, methyl iodide, and methyl triflate. More preferably the alkylating agent is dimethylsulfate. When the base is LDA, n-(C₁-C₈ alkyl) lithium, LiHMDS, NaHMDS or KHMDS, a solution of the ester is preferably cooled to from about -78°C, and more preferably about -20°C, to about 25°C prior to the addition of the base. After addition of the alkylating agent, the mixture is preferably heated to about 20°C to about 50°C. Heating is particularly useful when the alkylating agent is dimethylsulfate.

Alternatively, when R₁ is an optionally substituted benzyl group, the esterification can be accomplished by

1. (a) contacting a protected amino acid of formula (I) with an activating agent, i.e., activating the amino acid or forming an activated amino acid; and
2. (b) adding to the mixture of (a) a phenol optionally substituted on the phenyl ring with nitro, halogen, or cyano.

The use of activating agents, such as for example, alkyl chloroformates such as isobutyl chloroformate, CDI, and DCC, in esterification of acids with alcohols is well known to those skilled in the art. Preferred activating agents herein are CDI and DCC. Preferred esters in this process are those where R₁ is methyl or ethyl, more preferably methyl. A particularly preferred ester is (2S)-2-[(tert-butoxycarbonyl)amino]-3-(3,5-difluorophenyl)propanoic acid methyl ester. REFERENCE SCHEME 4 shows an alternate route to ester (II) . See also REFERENCE EXAMPLES 9 and 10. In the process of REFERENCE SCHEME 4, preferred 3,5-difluorobenzaldehyde (XII), which is commercially available from, for example, Aldrich, Milwaukee, Wisconsin, USA, is reacted with the phosphorous compound (XIII), where X₃ is a suitable leaving group, to produce olefin (XIV). Suitable leaving groups are known to those skilled in the art. A particularly preferred olefin (XIV) is methyl (2Z)-2-[[(benzyloxy)carbonyl]-3-(3,5-difluorophenyl)-2-propenonate.

The phosphorous compounds (XIII) are known to those skilled in the art. X₃ is preferably a C₁-C₃ alkyl group, more preferably methyl. The aldehyde (XII) and the phosphorous compound (XIII) are typically combined in a polar aprotic organic solvent, such as THF, MTBE, dioxane, ether or DME, and the resulting mixture, preferably a solution, is then cooled to about 0°. A base such as DBU or TMG is added and the contents of the mixture warmed to about 20-25°C and stirred until the reaction is complete, i.e., preferably to greater than about 90%, more preferably about 95%, and most preferably about 99%, conversion. Once the reaction is complete, the E- and Z-olefin isomers (XIV) are preferably separated since the Z isomer has the olefin stereochemistry preferred, and in some situations necessary, to yield the desired product. The separation is accomplished by methods known to those skilled in the art, such as, for example, by silica gel chromatography.

Next the olefin (XIV) is hydrogenated with a suitable hydrogenation catalyst to obtain the desired ester (II). The reaction may be conducted at pressures of from about 1 to about 100 psi. A variety of suitable catalysts will be recognized by those having ordinary skill in the art. An example of a class of suitable catalysts is represented by the formula [Rh(diene)L]⁺X^- where Rh is rhodium; diene is cyclooctadiene and norbornadiene; L is a ligand selected from the group consisting of DIPMAP, MeDuPhos, EtDuPhos, Binaphane, f-Binaphane, Me-KetalPhos, Me-f-KetalPhos, Et-f-KetalPhos, BINAP, DIOP, BPPFA, BPPM, CHIRAPHOS, PROPHOS, NORPHOS, CYCLOPHOS, BDPP, DEGPHOS, PNNP and X^- is ClO₄^-, BF₄^-, CF₃-SO₃^-, Cl^-, Br^-, PF₆^- and SbF₆^-.

This class is preferred for use in this process aspect, particularly when L is DIPMAP or EtDuPhos.

Those skilled in the art will recognize suitable specific procedures for this reduction, i.e., hydrogenation. Generally, olefin XIV is first dissolved in the solvent, either in the reaction vessel or the solution is later transferred to the vessel. Hydrogen and the desired catalyst are then introduced into the vessel. The hydrogen is typically added under pressure, e.g., from about 25-75 psi of hydrogen. The catalyst can be added neat or as a solution of the catalyst in, for example, methanol.

Some hydrogenation reactions will give racemic ester (II). Since the preferred stereochemistry of the ester (II) is (S)-, it is preferable to use the Z-olefin (XIV) with an appropriate hydrogenation catalyst. Suitable solvents for the hydrogenation include polar solvents such as THF and various alcohols, preferably C₁-C₅ alcohols, and most preferably methanol, ethanol, isopropanol. Another preferred solvent is THF. The solvent is preferably degassed. Further, it is preferable to purge the reaction vessel after dissolving the olefin (XIV) in the solvent and before introducing the catalyst.

The hydrogenation is preferably a chiral hydrogenation and is performed in a temperature range of from about 0° to about reflux; it is preferred that the reaction be performed in the temperature range from about 0° to about room temperature (20-25°). The chiral hydrogenation is performed under a pressure of from about one atmosphere to about 100 psig. It is preferred that the chiral hydrogenation be performed under a pressure of from about 1 atmosphere to about 70 psig; it is more preferred that the chiral hydrogenation be performed under a pressure of from about 10 psig to about 40 psig. The ester (II) is obtained in greater than 90% enantiomeric purity, preferably in greater than 95% enantiomeric purity. Hydrogenation can be performed in a variety of fashions, such as, for example, in batch mode or in a continuous mode.

REFERENCE SCHEME 5 and REFERENCE EXAMPLES 11 and 12 disclose another alternate process, to prepare ester II. The process of REFERENCE SCHEME 5 permits the changing of one nitrogen protecting group for another and in addition provides the free amine XV. For example, if one has a "BOC"-protected ester (II) and desires a "CBZ"-protected ester (II), the "BOC"-protected ester (II) is typically reacted with an acid such as hydrochloric acid in a suitable solvent such as methanol at temperatures of from about -20° to reflux to give the free amine (XV). Preferably the amine XV is, methyl (2S)-2-amino-3-(3,5-difluorophenyl)propionate. The free amine (XV) is then protected with a different nitrogen protecting group, such as "CBZ" to produce the corresponding and desired "CBZ"-protected ester (II).

The protected ester (II), preferably of (S)-stereochemisty, is then converted to the corresponding preferably (S)-protected ketone (III) by any one of a number of processes.

R₂ is -Cl. One of the processes for the transformation of the (S)-protected ester (II) to the corresponding (S)-protected ketone (III) is exemplified in REFERENCE EXAMPLE 16.

Generally, the protected ester (II) of preferably (S)-stereochemistry is combined with the dihalogenatedmethane reagent and to this mixture is then added a suitable base. It is preferable to add the base to the mixture of ester and dihalogenatedmethane rather than the other way around. Next, to the resulting base/ester/dihalogenatedmethane mixture is added a second portion of base. It is preferred to add the second portion of base to the existing mixture. Finally, the base/ester/dihalogenatedmethane is treated with acid. It is preferred that X² be -I. It is preferred that about 1 to about 1.5 equivalents of R₂CH₂X² be used.

The strong base should have a pK_b of greater than about 30. It is preferred that the strong base be selected from the group consisting of LDA, (C₁-C₈ alkyl)lithium, LiHMDS, NaHMDS and KHMDS; it is more preferred that the strong base be LDA. It is preferred that strong base be present in an amount of from about 2 to about 2.5 equivalents.

Examples of the second base include compounds selected from the group consisting of (C₁-C₄)alkyl lithium, phenyl lithium, (C₁-C₄)alkyl-Grignard and phenyl-Grignard. It is preferred that the second base be selected from the group consisting of phenyl lithium, n-butyl lithium, methyl magnesium bromide, methyl magnesium chloride, phenyl magnesium bromide or phenyl magnesium chloride; it is more preferred that the second base is n-butyl lithium. It is preferred that the second base be present in an amount of from about 1 to about 1.5 equivalents.

Suitable acids are those, which have a pk_a of less than about 10. It is preferred the acid be selected from the group consisting of acetic, sulfuric, hydrochloric, citric, phosphoric, benzoic acids and mixtures thereof; it is more preferred that the acid be hydrochloric or acetic acid.

A variety of solvents are operable for the process; the preferred solvent for the process is THF. The reaction can be performed in the temperature range from about -80° to about - 50°; it is preferred to perform the reaction in the temperature range of from about -75° to about -65°. It is preferred that the ketone (III) is tert-butyl (1S)-3-chloro-1-(3,5-difluorobenzyl)-2-oxopropylcarbamate.

The process of transforming the (S)-protected ester (II) to the corresponding (S)-protected ketone (III) can also be performed without the addition of a second base, see REFERENCE EXAMPLE 2. This process requires the presence of excess CH₂(R₂)X² and three or more equivalents of strong base, which has a pK_b of greater than about 30 followed by adding acid.

In addition, the (S) -protected ester (II) and also be transformed to the corresponding ketone (III) in a process which comprises:

1. (1) contacting R₂-CH₂-COOH with a strong base which has a pK_b of greater than about 30;
2. (2) contacting the mixture of step (1) with an ester of formula (II); and
3. (3) contacting the mixture of step (2) with an acid. In this process it is preferred that the strong base is selected from the group consisting of LDA, (C₁-C₈ alkyl) lithium, LiHMDS, NaHMDS and KHMDS; it is more preferred that the base is LDA. It is preferred that from about 2 to about 2.5 equivalents of the strong base be used. The same acids as discussed above are operable here also.

REFERENCE SCHEME 3 and REFERENCE EXAMPLE 15 sets forth an alternative way of preparing the ketone (III) from the amino acid (I). This process first transforms the amino acid (I) to the intermediate (XI) and then transforms the intermediate (XI) to the desired ketone (III). The transformation of the amino acid (I) to the intermediate (XI) comprises:

1. (1) contacting a protected amino acid of formula (I) with a reagent selected from the group consisting of thionyl chloride, SO₂Cl₂, phosphorous trichloride, oxalyl chloride, phosphorous tribromide, triphenylphosphorous dibromide, oxalyl bromide, 1,2-phenylenetrichlorophosphate and 2,4,6-trichloro-1,3,5-triazine. It is preferred that the reagent is thionyl chloride or oxalyl chloride. The intermediate (XI) is not isolated. It is preferred that the intermediate (XI) is t-butyl-(1S)-2-chloro-1-[3,5-difluorobenzyl]-2-oxoethylcarbamate. Intermediate (IX) is then transformed to the desired ketone (III) in a process which comprises:

1. (1) contacting a carbonyl compound of formula (XI) where X₁ is -Cl, -Br and imidazolyl with LiCH₂Cl or LiCH₂Br. This compound is then reacted with the anion derived from the CH₂R₂X² reagent. Various solvents are operable as is known to those skilled in the art; the preferred solvent is THF. The reaction should be performed in the cold, in a temperature range of from about -78° to about -50°.

The (S)-protected ketone (III) is then reduced to the corresponding (S)-alcohol (IV) or (IV-a) by means known to those skilled in the art for reduction of a ketone to the corresponding secondary alcohol, see EXAMPLE 3. In addition, European Patent Application EP 0 963 972 A2 and International Publication WO02/02512 of PCT/US01/21012 disclose alternate reagents which are operable and work well in the reduction. The reductions are carried out for a period of time between about 1 hour and about 3 days at temperatures ranging from about -78° to elevated temperature up to the reflux point of the solvent employed. It is preferred to conduct the reduction between about -78° and about 0°. If borane is used, it may be employed as a complex, for example, borane-methyl sulfide complex, borane-piperidine complex, or borane-tetrahydrofuran complex. The preferred combination of reducing agents and reaction conditions needed are known to those skilled in the art, see for example, Larock, R.C. in Comprehensive Organic Transformations, VCH Publishers, 1989.

The reduction of the (S)-protected compound (III) to the corresponding alcohol (IV) produces a second chiral center and produces a mixture of diastereomers at the second center, (S, R/S)-alcohol (IV). This diastereomeric mixture is then separated by means known to those skilled in the art such as selective low-temperature recrystallization or chromatographic separation, most preferably by recrystallization, column chromatrography or by employing commercially available chiral columns.

In another embodiment, the diastereomeric mixture produced by the non-selective reduction of the (S)-protected compound (III) is not separated but is directly converted into the epoxide. The epoxide diastereomers may then be separated into by means well known in the art. Or; the epoxide diastereomers may be reacted with the amine, R_CNH₂ to form compounds analogous to structure (VII-1, where R_c is 3-methoxybenzyl).

The diastereomers may be separated at this point, or further transformations may be carried out before the diastereomers are separated. For example, the separation of the diastereomers can be carried out after deprotecting the alcohol (VII) to form the free amine (VIII), or the separation may be carried out after the amine (VIII) is converted into structure (X.)

Alternatively, the (S)-protected compound (III) may be reduced to selectively form the S or the R alcohol as illustrated in scheme I where the S alcohol is selectively formed. The selective reduction will decrease the need for the separation of the diastereomers as discussed above and will increase the amount of the desired isomer that is formed. Ideally, a single diastereomer is formed during the reduction of the ketone to the alcohol and a separation is not necessary.

The alcohol (IV) is transformed to the corresponding epoxide (V) by means, known to those skilled in the art, see REFERENCE SCHEME 6 (above) and EXAMPLE 4. The stereochemistry of the (S)-(IV) center is maintained in forming the epoxide (V). A preferred means is by reaction with base, for example, but not limited to, hydroxide ion generated from sodium hydroxide, potassium hydroxide, lithium hydroxide and the like. Reaction conditions include the use of C₁-C₆ alcohol solvents; ethanol is preferred. Reactions are conducted at temperatures ranging from about -45° up to the reflux temperature of the alcohol employed; preferred temperature ranges are between about -20° and about 40°.

The protected epoxides of amino acids (V) are known to those skilled in the art as intermediates in the preparation of pharmaceutical agents useful as renin and HIV inhibitors, see for example US Patents 5,482,947, 5,508,294, 5,510,349, 5,510,388, 5,521,219, 5,583,238, 5,610,190, 5,639,769, 5,760,064 and 5,965,588. In addition, the protected epoxides (V) are intermediates useful in producing pharmaceuticals agents to treat Alzheimer's disease. The epoxides (V) are transformed to useful compounds by the process of SCHEME 2 and REFERENCE SCHEME 3 and EXAMPLES 5 through 8. The preferred compound is the compound of EXAMPLE 8.

The unprotected epoxide (V-unprotected) is useful in the same way. It can readily be protected to form the epoxide (V) or it can be reacted unprotected. In some instance the free amino group may interfere in the subsequent reactions but in others it will work quite well. In some instance it will be possible to put the N-terminal end on first and then open the epoxide to produce the desired compounds (X).

The compounds (X) are amines and as such form salts when reacted with acids. Pharmaceutically acceptable salts are preferred over the corresponding compounds (X) since they often produce compounds, which are more water soluble, stable and/or more crystalline. Pharmaceutically acceptable salts are any salt which retains the activity of the parent compound and does not impart any deleterious or undesirable effect on the subject to whom it is administered and in the context in which it is administered. Pharmaceutically acceptable salts include salts of both inorganic and organic acids. The preferred pharmaceutically acceptable salts include salts of the following acids hydrochloric, hydrobromic, hydroiodic, nitric, sulfuric, phosphoric, citric, methanesulfonic, CH₃-(CH₂)_n1-COOH where n₁ is 0 thru 4, HOOC-(CH₂)n₁-COOH where n₁ is as defined above, HOOC-CH=CH-COOH, φ-COOH. For other acceptable salts, see Int. J. Pharm., 33, 201-217 (1986).

The compounds (X) and pharmaceutically acceptable salts thereof are useful for treating humans who have Alzheimer's disease, for helping prevent or delay the onset of Alzheimer's disease, for treating patients with mild cognitive impairment (MCI) and preventing or delaying the onset of Alzheimer's disease in those who would progress from MCI to AD, for treating Down's syndrome, for treating humans who have Hereditary Cerebral Hemorrhage with Amyloidosis of the Dutch-Type, for treating cerebral amyloid angiopathy and preventing its potential consequences, i.e. single and recurrent lobar hemorrhages, for treating other degenerative dementias, including dementias of mixed vascular and degenerative origin, dementia associated with Parkinson's disease, dementia associated with progressive supranuclear palsy, dementia associated with cortical basal degeneration , diffuse Lewy body type of Alzheimer's disease. The compounds are preferably used in the treatment, prevention and/or alleviation of Alzheimer's disease.

The definitions and explanations below are for the terms as used throughout this entire document including both the specification and the claims.

• All temperatures are in degrees Celsius.
• TLC refers to thin-layer chromatography.
• HPLC refers to high pressure liquid chromatography.
• THF refers to tetrahydrofuran.
• psig refers to pounds of pressure per square inch.
• CDI refers to 1,1'-carbonyldiimidazole.
• DCC refers to dicyclohexylcarbodiimide.
• TMG refers to 1,1,3,3-tetramethylquanidine.
• DMF refers to dimethylformamide.
• DBU refers to 1,8-diazabicyclo[5.4.0]undec-7-ene.
• DBN refers to 1,5-diazabicyclo[4.3.0]non-5-ene.
• LDA refers to lithium diisopropylamide.
• LiHMDS, refers to lithium bis(trimethylsilyl)amide.
• NaHMDS refers to sodium bis(trimethylsilyl)amide.
• KHMDS refers to potassium bis(trimethylsilyl)amide.
• BOC refers to t-butoxycarbonyl; 1,1-dimethylethoxy carbonyl; (CH₃)₃C-O-CO-.
• Hunig's base refers to DIPEA, diisopropylethylamine, [(CH₃)₂CH]₂-N-CH₂CH₃.
• DMAP refers to dimethylaminopyridine, (CH₃)₂N-pyridin-1-yl.
• Saline refers to an aqueous saturated sodium chloride solution.
• Chromatography (column and flash chromatography) refers to purification/separation of compounds expressed as (support; eluent). It is understood that the appropriate fractions are pooled and concentrated to give the desired compound(s).
• CMR refers to C-13 magnetic resonance spectroscopy, chemical shifts are reported in ppm (δ) downfield from TMS.
• NMR refers to nuclear (proton) magnetic resonance spectroscopy, chemical shifts are reported in ppm (d) downfield from TMS.
• TMS refers to trimethylsilyl.
• -φ refers to phenyl (C₆H₅) .
• MS refers to mass spectrometry expressed as m/e, m/z or mass/charge unit. [M + H]⁺ refers to the positive ion of a parent plus a hydrogen atom. EI refers to electron impact. CI refers to chemical ionization. FAB refers to fast atom bombardment.
• ESMS refers to electrospray mass spectrometry.
• HRMS refers to high resolution mass spectrometry.

Pharmaceutically acceptable refers to those properties and/or substances which are acceptable to the patient from a pharmacological/toxicological point of view and to the manufacturing pharmaceutical chemist from a physical/chemical point of view regarding composition, formulation, stability, patient acceptance and bioavailability.

Pharmaceutically acceptable anion salts include salts of the following acids methanesulfonic, hydrochloric, hydrobromic, sulfuric, phosphoric, nitric, benzoic, citric, tartaric, fumaric, maleic, CH₃-(CH₂)_n-COOH where n is 0 thru 4, HOOC-(CH₂)_N-COOH where n is as defined above.

• -O-mesylate refers to -O-methanesulfonic acid.
• -O-tosylate refers to -O-toluenesulfonic acid.
• -O-triflate refers to -O-trifluoroacetic acid.

When solvent pairs are used, the ratios of solvents used are volume/volume (v/v).

When the solubility of a solid in a solvent is used the ratio of the solid to the solvent is weight/volume (wt/v).

DIPMAP refers to (R,R)-1,2-bis[(o-methoxyphenyl)-phenylphosphine]ethane.

MeDuPhos refers to 1,2-bis ((2S,5S)-2,5-dimethylphospholano)benzene.

EtDuPhos refers to 1,2-bis ((2S,5S)-2,5-dimethylphospholano)benzene.

Binaphane refers to (S,S)-1,2-Bis{S)-4,5-dihydro-3H-dinaphtho[2,1-c:1',2'-e]phosphepino}benzene.

f-Binaphane refers to (R,R)-1,1'-Bis{R)-4,5-dihydro-3H-dinaphtho[2,1-c:1',2'-e]phosphepino}ferrocene; "f" refers to ferrocenyl.

Me-KetalPhos refers to 1,2-Bis-[(2S,3S,4S,5S)-3,4-O-isopropylidene-3,4-dihydroxy-2,5-dimethyl]benzene.

Me-f-KetalPhos refers to 1,1'-Bis-[(2S,3S,4S,5S)-2,5-dimethyl-3,4-O-isopropylidene-3,4-dihydroxyphospholanyl]ferrocene.

Et-f-KetalPhos refers to 1,1'-Bis-[(2S,3S,4S,5S)-2,5-diethyl-3,4-O-isopropylidene-3,4-dihydroxyphospholanyl]ferrocene

BINAP refers to R-2,2'-bis(diphenylphosphino)-1,1'binaphthyl.

DIOP refers to (R,R)-2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)-butane.

BPPFA refers to R-1-[(S)-1'2-bisdiphenylphospino)ferrocenyl]- ethyldimethylamine.

BPPM refers to (2S,4S)-N-butoxycarbonyl-4-diphenylphosphino-2-diphenylphosphinomethylpyrrolidine.

CHIRAPHOS refers to (S,S)-2,3-bis(diphenylphosphino)butane.

PROPHOS refers to (S)-1,2-bis(diphenylphosphino)propane.

NORPHOS refers to (R,R)-5,6-bis(diphenylphosphino)-2-norbornene.

CYCLOPHOS refers to R-1-cyclohexyl-1,2-bis(diphenylphosphino)ethane.

BDPP refers to (2S,4S)-bis(diphenylphosphino)pentane.

DEGPHOS refers to 1-substituted (S,S)-3,4-bis-(diphenylphosphino)- pyrrolidine.

PNNP refers to N,N'-bis(diphenylphosphino)-N,N'-bis[(R)-1-phenyl]ethylenediamine.

Thionyl chloride refers to SOCl₂.

Phosphorous trichloride refers to PCl₃.

Oxalyl chloride refers to (COCl)₂.

Phosphorous tribromide refers to PBr₃.

Triphenylphosphorous dibromide refers to ϕ₃PBr₂.

Oxalyl bromide refers to (COBr)₂.

Ether refers to diethylether.

1,2-Phenylenetrichlorophosphate refers to

2,4,6-trichloro-1,3,5-triazine refers to MTBE refers to methyl t-butyl ether.

DME refers to dimethoxyethane.

The invention is illustrated further by the following examples, which are not to be construed as limiting the invention in scope to the specific procedures described in them.

The starting materials and various intermediates may be obtained from commercial sources, prepared from commercially available organic compounds, or prepared using well-known synthetic methods.

The following detailed examples describe how to perform the -processes of the invention and are to be construed as merely illustrative, and not limitations of the preceding disclosure. Those skilled in the art will recognize appropriate variations from the procedures both as to reactants and as to reaction conditions and techniques.

To a 1-L 3-neck round bottom flask equipped with a magnetic stirrer, nitrogen inlet and thermocouple is added (2S)-2-[(tert-butoxycarbonyl)amino]-3-(3,5-difluorophenyl)propanoic acid (I, 40 g, 0.133 moles, 1 equivalent) followed by THF (240 mL). Lithium hydroxide monohydrate (5.6 g, 0.133 moles, 1 equivalent) is added in a single portion and is allowed to stir for 30 min at which time, the contents are cooled to 0°. Once cooled, dimethyl sulfate (12.6 mL, 0.133 moles, 1 equivalent) is added dropwise via syringe and then stirred for 30 min. The mixture is then heated to about 50° and monitored (by HPLC) until 90% conversion had been achieved. At that time, the mixture is cooled to below 20° (solids form). The mixture is then poured into sodium bicarbonate (200 mL), stirred for 15 min then extracted with methyl t-butyl ether (200 mL). The phases are separated and the aqueous layer is extracted with methyl t-butyl ether (2 x 200 mL). The combined organic phases are washed with water (400 mL) dried over sodium sulfate, filtered and concentrated under reduced pressure to give a solid. This material is then recrystallized from hexanes to give the title compound, mp = 81°; NMR (DMSO-d₆) δ 7.51, 7.15-7.25, 4.43, 3.81, 3.00-3.26 and 1.49; CMR (DMSO-d₆) δ 172.43, 163.74, 161.20, 155.67, 142.58, 112.70, 120.23, 78.69, 54.71, 52.24, 39.25 and 28.37.

To a 1-L 3-neck round bottom flask equipped with a magnetic stirrer, nitrogen inlet, thermocouple and additional funnel is added (2S)-2-[(tert-butoxycarbonyl)amino]-3-(3,5-difluorophenyl)propanoic acid methyl ester (II, REFERENCE EXAMPLE 1, 10.0 g, 0.0317 moles, 1 equivalent) followed by THF (175 mL) then cooled to -78°. Once the mixture is cooled, iodochloromethane (9.25 mL, 0.127 moles, 4 equivalents) is added in one portion via syringe. The addition funnel is charged with LDA (79 mL, 0.158 moles, 5 equivalents, 2.0 M in heptane/THF) and is subsequently added dropwise to the mixture keeping the internal temperature below -70°. Once the addition is complete, the contents are stirred for 15 min at which time acetic acid (47.2 mL, 0.824 moles, 26 equivalents) is added dropwise via the addition funnel keeping the internal temperature below -65°. Once this addition is complete, the mixture is stirred for 15 min then warmed to 0° and poured into water (500 mL), saline (500 mL) and methyl t-butyl ether (500 mL) then transferred to a separatory funnel. The phases are separated and the aqueous phase is extracted with methyl t-butyl ether (2 x 250 mL). The combined organic phases are washed with saturated sodium bicarbonate (500 mL), sodium sulfite (500 mL) and water (500 mL). The organic phase is then dried over sodium sulfate, filtered and concentrated under reduced pressure to give a solid. The solid is recrystallized from heptane/i-propyl alcohol (10/1)to give the title compound, mp = 139°; NMR (DMSO-d₆) δ 7.47, 7.06-7.14, 4.78, 4.49, 3.20, 2.82 and 1.40; CMR (DMSO-d₆) δ 200.87, 163.74, 161.20, 142.74, 112.80, 102.13, 79.04, 58.97, 47.72, 34.95 and 28.30.

To a 250 mL 3-neck round bottom flask equipped with magnetic stir bar, nitrogen inlet and thermocouple, is added tert-butyl (1S)-3-chloro-1-(3,5-difluorobenzyl)-2-oxopropylcarbamate (III, REFERENCE EXAMPLE 2, 4.4 g, 0.0132 moles, 1 equivalent) followed by THF (20 mL) and ethanol (30 mL) then cooled to -78°. Once the mixture is cooled, sodium borohydride (2.0 g, 0.0527 moles, 4 equivalents) is added as a solid portion wise over 30 min keeping the internal temperature below -70°. Once this addition is complete, the contents are stirred for 2 hr at -78° then warmed to 0° and stirred an additional 1 hr. The mixture is quenched by the addition of saturated potassium bisulfate (15 mL) and water (15 mL). This slurry is stirred for 30 min at 20-25° then concentrated under reduced pressure to half its volume. The mixture is then cooled to 0° and stirred for 30 min. After this time, the resultant solids are collected by filtration and washed with water (2 x 50 mL) then dried under reduced pressure at 50° to give crude product. A syn/anti ratio of 4-9:1 has been observed. The desired product is recrystallized from hexanes/ethanol (25/1) to give the title compound, mp = 149°; NMR (DMSO-d₆) δ 6.89-7.16, 5.61, 3.64-3.83, 3.19, 2.69 and 1.41; CMR (DMSO-d₆) δ 163.67, 161.24, 155.44, 112.70, 101.55, 78.04, 72.99, 54.29, 48.24, 35.97 and 28.37.

To a 250 mL 3-neck round bottom flask equipped with magnetic stir bar, nitrogen inlet and thermocouple, is added tert-butyl (1S,2S)-3-chloro-1-(3,5-difluorobenzyl)-2-hydroxypropylcarbamate (IV, EXAMPLE 3, 3.5 g, 0.010 moles, 1 equivalent) followed by absolute ethanol (60 mL) and cooled to 0°. To this mixture is added potassium hydroxide (0.73 g, 0.013 moles, 1.25 equivalents) dissolved in absolute ethanol (10 mL) over 1 hr and the resulting suspension is warmed to 15-20° and stirred for 1 hr. At this time, water (100 mL) is added and the reaction contents are cooled to -5° and stirred for 30 min. The solids are collected by filtration and washed with cold water (2 x 25 mL) then dried under reduced pressure at 45° to give the title compound, mp = 133°; NMR (DMSO-d₆) δ 7.03, 3.61, 2.68-2.98 and 1.33; CMR (DMSO-d₆) δ 163.72, 161.29, 155.55, 143.35, 112.65, 101.80, 78.17, 53.42, 52.71, 44.90, 36.98 and 28.36.

The anti-diastereomer mp = 101°.

tert-Butyl (1S)-2-(3,5-difluorophenyl)-1-[(2S)-oxiranyl]ethylcarbamate (V, EXAMPLE 4, 245 mg, 0.82 mmol) is suspended in isopropyl alcohol (6 mL) and 3-methoxybenzylamine (160 µL, 1.22 mmol) is added with stirring at 20-25°. This mixture is heated to gentle reflux (bath temp 85°) under nitrogen for 2 hr, whereupon the resulting mixture is concentrated under reduced pressure to give the title compound. The title compound is purified by flash chromatography (2-5% methanol/methylene chloride; gradient elution) to give purified title compound.

tert-Butyl (1S, 2R)-1-(3,5-difluorobenzyl)-2-hydroxy-3-[(3-methoxybenzyl)amino]propylcarbamate (VII, EXAMPLE 5, 258 mg, 0.59 mmol) is dissolved in methylene chloride (1 mL) at 20-25°, and trifluoroacetic acid (1 mL) is added with stirring under nitrogen. The mixture is stirred at 20-25° for 1 hr, whereupon the mixture is concentrated under reduced pressure to give the title compound. The title compound is used in the next reaction without further purification.

(2R,3S)-3-amino-4-(3,5-difluorophenyl)-1-[(3-methoxybenzyl)amino]-2-butanol (VIII, EXAMPLE 6) is dissolved in anhydrous DMF (3 mL) and cooled to 0°. Triethylamine (500 µL, 3.6 mmol) and 5-methyl-N,N-dipropylisophthalamic acid (IX, 156 mg, 0.59 mmol) are added with stirring. The mixture is warmed to 20-25° briefly to allow for complete dissolution of the carboxylic acid, before recooling to 0°. 1-Hydroxybenzotriazole (157 mg, 1.2 mmol) is added with stirring, followed by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (229 mg, 1.2 mmol). The resulting mixture is stirred at 0° for 5 min, then warmed to 20-25° for 15 hr. The mixture is then quenched with aqueous citric acid (10%), and the mixture extracted three times with ethyl acetate. The combined organic extracts are washed with saturated sodium bicarbonate, saline, dried over sodium sulfate, filtered and concentrated under reduced pressure to give the title compound in crude form. This material is purified by flash chromatography (2-10% methanol/methylene chloride gradient elution) to give purified title compound, MS (ES) MH⁺ = 582.3.

Following the general procedure of EXAMPLES 5, 6 and 7 and making non-critical variations but using 3-iodobenzylamine, the title compound is obtained.

3,5-Difluorobenzaldehyde (XII, 2.87 g, 0.02 moles, 1 equivalent) and THF (100 mL) are mixed and cooled to about 0°. N-(Benzyloxycarbonyl)phosphonyl-glycinetrimethylester (XIII, 8.7 g, 0.026 moles, 1.3 equivalents) is added to the 3,5-difluorobenzaldehyde (XII)/THF mixture. This is followed by 1,1,3,3-tetramethyl guanidine (4.0 mL, 0.032 moles, 1.56 equivalents) added dropwise. The reaction is stirred for 5 min at 0° then allowed to warm to 20-25°. After 2 hr, the reaction is complete (by TLC analysis) at which time water (100 mL) and ethyl acetate (100 mL) are added. The phases are separated and the aqueous phase is extracted with ethyl acetate (100 mL) and the combined organic phases are washed with saline (100 mL), dried over sodium sulfate, filtered and concentrated under reduced pressure to give a crude solid. The solid is purified by silica gel chromatography (ethyl acetate/hexanes; 15/85) to give the title compound, mp = 112°; NMR (CDCl₃) δ 7.19, 7.06, 6.86, 6.15, 6.43, 4.97 and 3.69; CMR (CDCl₃) δ 165.56, 164.54, 164.41, 162.07, 137.39, 136.02, 128.97, 128.80, 128.62, 128.57, 128.47, 126.25, 112.57, 112.38, 105.22, 104.97, 104.72, 68.17 and 53.33. Additional material is recovered that is a mixture of E and Z olefins.

Methyl (2Z)-2-([(benzyloxy)carbonyl]-3-(3,5-difluorophenyl)-2-propenonate (XIV, XIV, REFERENCE EXAMPLE 9, 0.100 g, 0.228, mmol) and degassed methanol (10 ml) are mixed in a 100 mL Hastelloy bomb. The mixture is purged three times with hydrogen (60 psig) and then stirred at 60 psig hydrogen for 60 min at 20-25°. Then (R,R,)-DIPAP)Rh (5.2 mg, 3 mole%) is dissolved in methanol (1 mL, degassed) is added and the system purged with hydrogen (3 x 60 psig). The contents are then stirred at 20 psig hydrogen at 25° overnight at which time the reaction is complete as determined by HPLC. The system is then purged and filtered to remove the catalyst and the solvent is removed under reduced pressure to give the title compound.

(2S)-2-[(tert-butoxycarbonyl)amino]-3-(3,5-difluorophenyl)propanoic acid methyl ester (II, REFERENCE EXAMPLE 1, 0.60 g (0.002 moles, 1 equivalent), methanol (20 mL) and hydrochloric acid (3N, 20 mL) are mixed. The mixture is then heated to 50° and stirred until complete as measured by HPLC. When the reaction is complete, the contents are cooled to 20-25° and the pH of the mixture is adjusted to 8 with saturated sodium bicarbonate and then concentrated under reduced pressure. This mixture is extracted with ethyl acetate (2 x 20 mL) and the combined organic phases are dried over sodium sulfate, filtered and concentrated, HPLC (Retention time = 2.89 min; Zorbax RX-C8 acetonitrile/0.05M potassium dihydrogen phosphate, 60/40; 1.0 mL/min, λ=210 nm.

This material is carried on without further purification into the next step.

Methyl (2S)-2-amino-3-(3,5-difluorophenyl)propanoate (XV, REFERENCE EXAMPLE 11, 0.300 g, 1.40 mnol, 1 equivalent) and water (10 mL) are mixed. Sodium carbonate (0.15 g, 1.40 mmol, 1 equivalent) of is added followed by benzylchloroformate (0.2 mL, 0.24 g, 1.4 mmol, 1 equivalent) and the mixture stirred at 20-25° until complete as measured by HPLC. Once the reaction is complete, ethyl acetate (20 mL) is added and the phases separated. The aqueous phase is extracted with ethyl acetate (2 x 20 mL), and the combined organic phases are dried over sodium sulfate, filtered, and concentrated. The concentrate is crystallized from hexanes/ethyl acetate to give the title compound, mp = 54°; NMR (DMSO-d₆) δ 7.84, 7.28, 7.06, 4.98, 4.35, 3.68, 3.12 and 2.88.

(2S)-2- [(tert-butoxycarbonyl)amino]-3-(3,5-difluorophenyl)propanoic acid (I, 5.0 g, 0.017 moles, 1.0 equivalent) and potassium carbonate (2.5 g, 0.018 moles, 1.1 equivalent) are mixed in THF (100 mL). To this heterogeneous mixture is then added dimethyl sulfate (1.6 mL, 2.1 g, 0.017 moles, 1.0 equivalent) and the contents were then stirred at 20-25° overnight. Once the reaction is complete as measured by HPLC, ammonium hydroxide (10%, 20 mL) is added and allowed to stir for 1 hr at which time the contents are extracted with ethyl acetate (3 x 50 mL). The combined organic phases are washed with water (50 mL) and saline (50 mL), dried over sodium sulfate, filtered, and concentrated under reduced pressure to give the title compound.

(2S)-2-[(tert-butoxycarbonyl)amino]-3-(3,5-difluorophenyl)propanoic acid (I, 5.0 g, 0.017 moles, 1.0 equivalent) and potassium carbonate (2.5 g, 0.018 moles, 1.1 equivalent) and DMF (100 mL) are mixed. To this heterogeneous mixture is then added dimethyl sulfate (1.6 mL, 2.1 g, 0.017 moles, 1.0 equivalent) and the contents are then stirred at 20-25° overnight. Once the reaction is complete as measured by HPLC, ammonium hydroxide (10%, 20 mL) is added and allowed to stir for 1 hr. The contents are stirred for 30 min then cooled to 0° and filtered. The solids are washed with cold water (20 mL) and dried under reduced pressure to give the title compound.

(2S)-2-[(tert-butoxycarbonyl)amino]-3-(3,5-difluorophenyl)propanoic acid (I) is dissolved in THF and stirred at 20-25°. Oxalyl chloride (1 equivalent) is added and the mixture stirred for about 15 min to give t-butyl-(1S)-2-chloro-1-[3,5-difluorobenzyl]-2-oxoethylcarbamate (XI). The mixture is cooled to <0° and LiCHICl (greater than 2 equivalents) is added. The mixture is stirred until the reaction is complete. The reaction is quenched with water and the product is extracted into ethyl acetate. The combined organic phases are washed with saline, dried over sodium sulfate and concentrated under reduced pressure to give the title compound.

ICH₂Cl (3.54 g, 1.46 mL, 19,.82 mmol, 1.25 equivalent) and THF (5 mL) are added to (2S)-2-[(tert-butoxycarbonyl)amino]-3-(3,5-difluorophenyl)propanoic acid methyl ester (II, REFERENCE EXAMPLE 1, 5 g, 15.86 mmol, 1 equivalent). The mixture is cooled to -78° and LDA (22.3 mL, 44.60 mmol, 2.25 equivalents, 2.0M) is added dropwise maintaining an internal temperature below -60°. Once the addition is complete, the contents are stirred for 30 min at -78° at which time n-butyllithium (15.3 mL, 19.82 mmol, 1.25 equivalents; 1.3M in hexanes) is added dropwise maintaining an internal temperature below about -60°. The reaction is stirred for 30 min then quenched into 0° hydrochloric acid (IN). Ethyl acetate is added and the phases are separated and the aqueous phase is extracted with ethyl acetate. The combined organic phases are washed with saturated sodium bicarbonate, dried over sodium sulfate, filtered and concentrated under reduced pressure to give the title compound, NMR (DMSO-d₆) δ 7.47, 7.06-7.14, 4.78, 4.49, 3.20, 2.82 and 1.40; CMR (DMSO-d₆) δ 200.87, 163.74, 161.20, 142.74, 112.80, 102.13, 79.04, 58.97, 47.72, 34.95 and 28.30.

tert-butyl (1S,2S)-3-chloro-1-(3,5-difluorobenzyl)-2-hydroxypropylcarbamate (IV, EXAMPLE 3, 1.0 gm, 2.98 mmol) and Dowex50WX2-400 resin (4.6 gm, 23.8 mmol) and methanol (25 mL) are mixed. The mixture is then placed over a J-Kim shaker with heating at 50° for 2 hr. ESMS analysis indicates no starting material left in the mixture. The reaction contents are filtered through a sintered funnel and the resin washed with methanol (25 mL) and methanol/methylene chloride (1/1, 25 mL). The resulting mixture is eluted with ammonia in methanol (2N, 2 x 25 mL). The eluate is concentrated under reduced pressure to give the title compound, ESMS - 236.1.

(1S,2S)-3-chloro-1-(3,5-difluorobenzyl)-2-hydroxypropylamine (REFERENCE EXAMPLE 17, 33 mg, 0.14 mmol) and absolute ethanol (1.5 mL) are mixed. Potassium hydroxide (9.8 mg, 0.175 mmol) in absolute ethanol (0.5 mL) is added to this mixture and the resulting mixture is stirred at 20-25 deg for 30 min. At this time ESMS indicates formation of the product (MH⁺ = 200.1). Water (2 mL) is added and mixture is concentrated under reduced pressure to half the volume and then diluted with ethyl acetate (15 mL). The organic phase is separated and the aqueous phase is extracted with ethyl acetate (2 x 10 mL). The organic phases are combined, washed with saline and dried over anhydrous magnesium sulfate. The solvent is removed under reduced pressure to give the title compound, MH⁺ = 200.1.

The invention and the manner and process of making and using it, are now described in such full, clear, concise and exact terms as to enable any person skilled in the art to which it pertains, to make and use the same. It is to be understood that the foregoing describes preferred embodiments of the invention and that modifications may be made therein without departing from the spirit or scope of the invention as set forth in the claims. To particularly point out and distinctly claim the subject matter regarded as the invention, the following claims conclude this specification.