The title enantiomer has been obtained by resolution of the racemic acid (I). Acid (I) is activated as the mixed anhydride (II) with pivalic acid and triethylamine. Subsequent coupling of anhydride (II) with the potassium anion of (S)-4-benzyl-2-oxazolidinone leads to a mixture of the diastereoisomeric imides (III) and (IV), which can be separated by column chromatography and recrystallization. Then, removal of the chiral auxiliary from the target isomer (III) by hydrolysis with lithium peroxide furnishes the desired (S)-enantiomer.

In an enantioselective synthesis of the (S)-enantiomer, asymmetric alkylation of the chiral N-butyryl oxazolidinone (I) with benzyl 5-bromomethyl-2-methoxybenzoate (II) in the presence of lithium hexamethyldisilazide leads to isomer (III) in high diastereomeric excess. Subsequent benzyl ester hydrogenolysis in (III) employing Pd/C affords carboxylic acid (IV), which is further converted to the mixed anhydride (V) with ethyl chloroformate and triethylamine. Coupling of anhydride (V) with 4-trifluoromethylbenzylamine (VI) furnishes the corresponding amide (VII). The chiral auxiliary is then removed from (VII) by hydrolysis with lithium peroxide to yield the target (S)-enantiomer.