Scheme 1. Synthesis of fluorescent probes. Reagents and conditions: (i) HATU, DIPEA, DMF, rt, 1 h; (ii) (1) DBU, HOAt, DMF, rt, 20 min; (2) 8 or 9, HATU, DIPEA, DMF, rt, 10 h; (iii) TFA (9 equiv.), CH2Cl2, 0 °C to rt, 3 h; (iv) for compounds 13, 15, 17 and 18: HATU, dye, DIPEA, DMF, rt, 10 h; for compound 12: EDC·HCl, HOAT, dye, DIPEA, DMF, rt, 10 h; for compound 14: dye, DIPEA, DMF, rt, 10 h; for compound 16: see the ESI.†.
