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Synthesis of the ‘853 derivatives with modifications in positions 3 or 4, reagents, and conditions: (a) EDC × HCl, HOAt, DMF, rt (3a: 39%, 3b: 57%, 3c: 29%, 4: 31%); (b) AcCl, pyridine, DMAP, 0 °C to rt, 2 h (72%), (c) NaH, MeI, DMF, rt, 1 h (77%); (d) 1.25 M HCl in MeOH, 115 °C, 2 h (100% crude); (e) N2H4, EtOH, 70 °C, 17 h (15%).
