Reagents and conditions:
(a) Boc-glycine, HATU, DIPEA, DMF-DCM, rt, 71%; (b) trifluoroacetic
anhydride, pyridine, THF, 0 °C, 92%; (c) (i) TFA, MeCN, 0 °C,
24h; (ii) HCl, diethylether, 84%; (d) HATU, DIPEA, R-COOH or 1-chloro-N,N,2-trimethylprop-1-en-1-amine, RCOOH,
TEA or RCOCl, TEA, 20–76%.