Figure 2. Synthesis of 3β-NBD-TCA: a) SOCl2, dry MeOH, 0 °C → rt, 18 h; b) Et3N, CH3SO2Cl, dry DCM, 0 °C, 2 h; c) NaN3, dry DMF, 80 °C, 48 h; d) PPh3, H2O, THF, 50 °C, 18 h; e) NBDCl, NaHCO3, MeOH, 50 °C, 18 h; f) 2N LiOH, MeOH, 40 °C, 3 h; g) Et3N, TBTU, HOBt, dry DMF, 45 min, then S11 in DMF, rt, 18 h; h) 2N NaOH in MeOH, DCM, rt, 3 h; i) 40 % aq. nBu4NOH in H2O, Boc2O, acetone, rt, 18 h; j) (COCl)2 in dry DCM, dry DMF, 0 °C, 1 h, then Et3N, CF3CH2OH in dry DCM, rt, 18 h; k) TFA, DCM, rt, 4 h.
