but extensive epimerization at Pro2 was observed. Similarly, saponification of 12 and coupling with either 2a or H-Phe-OMe and 2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate/1-hydroxy-1H-benzotriazole (TBTU/HOBt) gave the corresponding endothiopeptides as mixtures of two epimers. The synthesis of the pure diastereoisomer BzΨ[CS]-Aib-Pro-AibΨ[CS]-N(Me)Ph (21) was achieved via isomerization
                                    甲基的反应ñ - (2,2-二甲基-2- ħ -azirin -3-基)-
L-脯氨酸(2A在室温下用
硫代苯甲酸),得到endothiopeptide的Bz-AIB Ψ [CS] -Pro-OME(7)高产。以类似的方式,(苄氧基)羰基(Z)保护的脯
氨酸转化
硫代酸,将其用反应图2a,得到endothiotripeptide Z-Pro的-AIB Ψ [CS] -Pro-OME(12)。通过皂化,形成混合酸酐并用H 2 S处理原位制备相应的7
硫代酸。与2a的第二次反应导致产生了endodithiotetrapeptide 9,但在Pro 2观察到广泛的差向异构。同样,将12皂化并与2a或H-Phe-OMe和2-(1 H-苯并三唑-1-基)-1,1,3,3-四甲基
脲四
氟硼酸酯/ 1-羟基-1 H-苯并三唑偶合( TBTU / 
HOBt)以两种差向异构体的混合物形式给出了相应的内
硫肽。纯对映异构体的合成的Bz