Scheme 1.

Synthesis of FP probe^a

^aReagents and conditions: (a) pTsOH, acetone, 3 h, quant. yield; (b) propane-1,3-diamine, TEA, EtOH, 60 °C, 2 h then; CF₃CO₂Et, TEA, MeOH, 12 h, 89 %; (c) isoindoline-1,3-dione, PPh₃, DIAD, THF, 2 h, 90 %; (d) NH₂NH₂, MeOH, 8 h, 63 %; (e) tert-butyl (S)-2-((tert-butoxycarbonyl)amino)-4-oxobutanoate, NaBH₃CN, AcOH, MeOH, 2 h, 67 %; (f) 3-(3-oxoprop-1-yn-1-yl)benzonitrile, NaBH₃CN, AcOH, MeOH, 2 h, 79 %; (g) K₂CO₃, H₂O₂, DMSO, quant. yield; (h) NH₄OH, MeOH, 77 %; (i) TFA, H₂O, 8 h, 37 %; (j) fluorescein, DIC, HOBt, DIPEA, DMF; 12 h then TFA, H2O, 8 h, 29 %.