合成路线1

Partial hydrolysis of dimenthyl (R,R)-cyclopropane-1,2-dicarboxylate (I), followed by treatment of the resultant mono-carboxylic acid with SOCl2, afforded acid chloride (II). The coupling of the organozincate reagent prepared from (9-xanthyl)methyl iodide (III) and Zn-Cu with acid chloride (II) in the presence of palladium catalyst gave rise to ketone (IV). Basic hydrolysis of the remaining menthyl ester function of (IV) afforded keto acid (V). Reaction of (V) with potassium cyanide and ammonium carbonate produced hydantoin (VI) as a diastereomeric mixture. Chromatographic separation of the diastereoisomers was achieved after hydantoin N-alkylation and simultaneous esterification of (VI) with p-methoxybenzyl chloride (VII) and KHCO3 in hot DMF. Hydantoin hydrolysis from the desired (S,R,R)-isomer (VIII) upon heating with aqueous Ba(OH)2 at 200 C in a pressure vessel furnished the title amino acid compound.