Scheme 3.
Reagents and conditions: (a) N,O-dimethylhydroxylamine hydrochloride, EDC·HCl, HOBt, TEA, DMF, rt, 12 h, 90%; (b) thiazole or benzothiazole, n-BuLi, −78 °C, 2.5 h, 70%; (c) formic acid, rt, 12 h, 100%; (d) HNR1R2, EDC·HCl, HOBt, DMF, rt, 12 h, 90%; (e) triflic acid, DCM, rt, 5 min, 100% (f) Cbz-AA-OH, HOBt, EDC·HCl, DMF, rt, 12 h followed by HPLC purification.
