合成路线1

Esterification of N-(benzyloxycarbonyl)-L-aspartic acid beta-tert-butyl ester (I) by means of diazomethane provided the alpha-methyl ester (II), which was subsequently sulfenylated using (2,4-dinitrophenyl)-(4-methoxybenzyl)disulfide (III) in the presence of n-BuLi to furnish the (2R,3R)-sulfide (IV) as the major isomer. Reduction of the methyl ester group of (IV) with DIBAL, followed by Wittig-Horner reaction of a postulated aldehyde aluminoxyacetal intermediate with neopentyl diethoxyphosphoryl methanesulfonate produced the alpha,beta-unsaturated sulfonate ester (V). Reduction of the double bond of (V) employing [(PPh3)CuH]6 in neutral medium afforded the saturated ester (VI) with only a small epimerization at the C2 position. The tert-butyl ester of (VI) was then deprotected with trifluoroacetic acid yielding the free acid (VII).