合成路线1

L-3-Formyl-N-acetyltyrosine methyl ester (XII) was protected as the dithioacetal (XIII) using ethanedithiol and boron trifluoride etherate. After conversion of the phenol group of (XIII) into aryl triflate (XIV) upon treatment with N-phenyltrifluoromethanesulfonimide, its carboxylation with carbon monoxide in MeOH-DMSO in the presence of palladium catalyst generated the methyl ester (XV). Selective hydrolysis of the aliphatic ester of (XV) with LiOH at low temperature provided carboxylic acid (XVI), which was then coupled with the racemic amine (XI) to afford amide (XVII) as a diastereomeric mixture. Hydrolysis of the thioketal group of (XVII) to give aldehyde (XVIII) was achieved by treatment with mercuric perchlorate. The remaining methyl ester of (XVIII) was hydrolyzed with LiOH, and the desired diastereoisomer was finally isolated by RP-HPLC.