Scheme 3.

Synthesis of reduction triggered desferrioxamine-ciprofloxacin conjugate 13. Reagents and conditions: (i) SOCl₂, MeOH, reflux, 77%; (ii) NaN₃, MeOH-H₂O, rt, 91%; (iii) 1. PPh₃, CH₂Cl₂, rt; 2. AcOH, THF-H₂O, reflux, 66%; (iv) 1. COCl₂, toluene, rt; (v) desferrioxamine mesylate, Et₃N, DMF, 0°C-rt, 74% for 2 steps; (vi) LiOH, MeOH-H₂O, rt, 90%; (vii) ciprofloxacin, EDC, HOBt, Et₃N, DMAP, DMF, 0°C-rt, 60%