Racemic cyclohexylphenyl glycolic acid (CHPGA) (I) is dissolved with (L)-tyrosine methyl ester (II) in refluxing acetonitrile/water to yield a mixture of diastereomeric salts, which is resolved by crystallization to afford the desired diastereomeric salt [(S)-CHPGA-(L)-TME] (III). Finally, the hydrolysis of salt (III) with HCl or H2SO4 at 40-50篊 in toluene yields the enantiomer (IV). Alternatively intermediate (IV) can be obtained as follows: acetalization of (S)-mandelic acid (V) with pivaldehyde (VI) in pentane and catalytic TfOH provides derivative (VII), which is then treated with LHMDS and then condensed with cyclohexanone (VIII) in THF to furnish aldol adduct (IX). Elimination of tertiary alcohol in (IX) with SOCl2 and pyridine in THF gives derivative (X), which is then converted into intermediate (IV) either by first hydrolysis of lactone (X) with KOH in MeOH and subsequent hydrogenation of the obtained derivative (XI) over Pd/C in MeOH, or by first hydrogenation of (X) over Pd/C in MeOH to give (XII), followed by hydrolysis with KOH in MeOH. On turn, derivative (XII) can alternatively be synthesized by treatment of derivative (VII) with LHMDS, followed by reaction with 3-bromocyclohexene (XIII) in THF to provide derivative (XIV), which is then hydrogenated over Pd/C.

The desired product is finally obtained by first formation of a mixed anhydride (XVI) by reaction of the cyclohexylphenyl glycolic acid (IV) with isobutylchloroformate (XV) in cyclohexane in the presence of Et3N, followed by treatment with 4-N,N-diethylamino butynol (XVII) (obtained on turn from reaction of propargyl alcohol (XVIII) with diethylamine (XIX) in the presence of paraformaldehyde and CuCl.

Racemic cyclohexylphenyl glycolic acid (CHPGA) (I) is dissolved with (L)-tyrosine methyl ester (II) in refluxing acetonitrile/water to yield a mixture of diastereomeric salts, which is resolved by crystallization to afford the desired diastereomeric salt [(S)-CHPGA-(L)-TME] (III). Finally, the hydrolysis of salt (III) with HCl or H2SO4 at 40-50篊 in toluene yields the enantiomer (IV). Alternatively intermediate (IV) can be obtained as follows: acetalization of (S)-mandelic acid (V) with pivaldehyde (VI) in pentane and catalytic TfOH provides derivative (VII), which is then treated with LHMDS and then condensed with cyclohexanone (VIII) in THF to furnish aldol adduct (IX). Elimination of tertiary alcohol in (IX) with SOCl2 and pyridine in THF gives derivative (X), which is then converted into intermediate (IV) either by first hydrolysis of lactone (X) with KOH in MeOH and subsequent hydrogenation of the obtained derivative (XI) over Pd/C in MeOH, or by first hydrogenation of (X) over Pd/C in MeOH to give (XII), followed by hydrolysis with KOH in MeOH. On turn, derivative (XII) can alternatively be synthesized by treatment of derivative (VII) with LHMDS, followed by reaction with 3-bromocyclohexene (XIII) in THF to provide derivative (XIV), which is then hydrogenated over Pd/C.

The catalytic enantioselective cyanosilylation of the ketone (I) by means of Tms-CN catalyzed by gadolinium isopropoxide and the chiral ligand (II) in THF/propionitrile gives the silylated cyanohydrin (III), which is reduced by means of DIBAL in toluene to yield the carbaldehyde (IV). The desilylation of (IV) by means of HCl in aqueous THF affords the hydroxyaldehyde (V), which is finally oxidized by means of NaClO2 in tert-butanol/water to provide the target (S)-2-cyclohexyl-2-hydroxy-2-phenylacetic acid intermediate (VI) (see Scheme no. 23604001a, intermediate (IV)).