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[摘要]：Previous syntheses of histidinoalanine (HAL) have led to mixtures of regioisomers and/or stereoisomers. For example, opening of N-Cbz-D-serine-beta-lactone (6) with Boc-L-His-OMe (5) gave a 2:1 mixture of tau- and pi-regioisomers. The sulfamidate 10, derived from N-benzyl-D-serine methyl ester (11), was reacted with Boc-L-His-OMe (5) to give the tau-HAL derivative 17 as a single isomer in 57% yield. A similarly prepared tau-HAL 19, bearing protecting groups that were all hydrogenolytically labile, led to the free bis-amino acid, tau-L-histidinyl-D-alanine (tau-4), as a salt-free standard for amino acid analysis. |
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