Reagents and conditions: (a)
HATU, DIPEA, DMF, rt, overnight, yield 49–59%; (b) NaOH, MeOH,
rt, 2 h, yield 71–85%; (c) CF3COOH, DCM, 40 °C,
3 h, yield 62–77%; (d) HATU, DIPEA, DMF, rt, overnight, yield
53–85%; (e) NH2OH-HCl, KOH, MeOH, rt, 2 h, yield
43–83%.