合成路线1

The intermediate 3-methyl 2(S)-(2-oxoperhydropyrimidin1-yl)butyric acid (XIII) has been obtained as follows: The oxidation of 3-(benzyloxycarbonylamino)-1-propanol (XVII) with oxalyl chloride in dichloromethane gives the corresponding aldehyde (XVIII), which is reductocondensed with L-valine methyl ester (XIX) by means NaBH3CN in methanol yielding the N-substituted valine (XX). The cyclization of (XX) by elimination of the benzyloxycarbonyl group by hydrogenation with H2 over Pd/C in dichloromethane, followed by reaction with carbonyldiimidazole (CDI) affords the 3-methyl 2(S)-(2-oxoperhydropyrimidin-1-yl)butyric acid methyl ester (XXI). Finally, this compound is hydrolyzed with LiOH in dioxane/water to afford the target intermediate (XIII).