Reagents and conditions: a: i) (Boc)2O, TEA, DCM, r.t., 2 h; ii) MeOH, EDCI, HOBt, TEA, DMAP, DCM, 10 h;
b: NaBH4, MeOH, THF, reflux, 4 h;
c: I2, PPh3, imidazole, DCM, 0 °C-rt, 2 h;
d: Troc-L-Cys-OMe, TEA, DMF, 85 °C, 2 h;
e: i) TFA, r.t., 30 min; ii) C15H31COOH, EDCI, HOBt, TEA, DMAP, DMF, 60 °C, 10 h;
f: i) Zn dust, AcOH, H2O, THF, r.t., 1 h; ii) (Boc)2O, TEA, DCM, r.t., 1 h;
g: i) Ba(OH)2, THF/H2O, 60 °C, 1 h; ii) H-L-Ser(tBu)-OMe•HCl, EDCI, HOBt, EDIPA, DMAP, DMF, 60 °C, 10 h;
h: TFA, r.t., 30 min.