[(S)-2-tert-Butoxycarbonylamino-4-(5-methyl-2,4-dioxo-3,4-dihydro-2H-pyrimidin-1-yl)-butyrylamino]-acetic acid 、 [(S)-2-Amino-4-(5-methyl-2,4-dioxo-3,4-dihydro-2H-pyrimidin-1-yl)-butyrylamino]-acetic acid ethyl ester; compound with trifluoro-acetic acid 在
1-羟基苯并三唑 、
三乙胺 、
N,N'-二环己基碳二亚胺 作用下,
以
N,N-二甲基甲酰胺 为溶剂,
以61%的产率得到[(S)-2-{2-[(S)-2-tert-Butoxycarbonylamino-4-(5-methyl-2,4-dioxo-3,4-dihydro-2H-pyrimidin-1-yl)-butyrylamino]-acetylamino}-4-(5-methyl-2,4-dioxo-3,4-dihydro-2H-pyrimidin-1-yl)-butyrylamino]-acetic acid ethyl ester