Scheme 3.

Synthesis of 3a–3f^a

^aReagents and conditions: (a) H₂, Pd/C, MeOH, overnight; (b) monometyl suberate, EDC, HOBt, DIPEA, CH₂Cl₂, 0 °C–rt, 6 h; (c) 8, K₂CO₃, acetone, reflux, 6 h; (d) NH₂OH, KOH, 0 °C–rt, 3 h; (e) BnBr or 4-nitrobenzyl bromide, NaH, DMF, 0 °C–rt, 4 h; (f) SnCl₂·2H₂O, MeOH, reflux, 2 h; (g) NaNO₂, AcOH–H₂O (9:1), 0 °C, 10 min, NaN₃, 0 °C–rt, 1 h; (h) (Boc)₂O, Et₃N, CH₂Cl₂, rt, 4 h; (i) 12, EDC, HOBt, DIPEA, CH₂Cl₂, 0 °C–rt, 6 h.