Scheme 4. Synthesis of GC-2a and GC-2b.
Reagents and conditions: a) i. NaOMe, MeOH, rt ii. Pd(OH)2, EtOH, H2, over two steps 75% b) i. Ac2O, Pyridine, DMAP, 78% ii. DMF, NaN3, 90% c) CuSO4.5H2O, C6H7O6Na, t-BuOH/H2O, 70% d) MeOH, NaOMe, rt ,90% e) CuSO4.5H2O, C6H7O6Na, t-BuOH/H2O, 70% f) MeOH, NaOMe, rt, 90%