For 2 R - Ac, X = Boc-L-Cys(S)-OMe TLC R f = 0.40 (2:1 hexane/EtOAc); 2 R = ZL-Ala X = Boc-L-Cys(S)-OMe TLC R f = 0.29 (2:1 hexane/EtOAc); HRMS: (M+H)+ Calcd for C 23 H 26 N 7 S 3 : 524.0871; Found: 524.0872; 3ab X - Boc-L-Cys(5)-OMe HPLC RP C 18 40 %