Scheme 2.

Synthesis of 2a–2b^a

^aReagents and conditions:(a) ethyl chlorooximidoacetate, Na₂CO₃, THF–H₂O (1:1), 0 °C–rt, 18 h; (b) 2N NaOH, MeOH–THF (1:1), 0 °C–rt, 1 h; (c) EDC, HOBt, methyl 7-aminoheptanoate hydrochloride, DIPEA, CH₂Cl₂, rt, 4 h; (d) TFA, CH₂Cl₂, rt, 4 h; (e) NaNO₂, AcOH–H₂O, 0 °C, 10 min, then NaN₃, 0 °C–rt, 1 h; (f) 12, DCC, HOBt, DMAP, CH₂Cl₂, 0 °C–rt, 6 h; (g) NH₂OH, KOH, MeOH, 0 °C–rt, 3 h.