A solution of thiocolchicoside (2.3 g, 3.96 mmol) in phosphoric acid (85-88%, 65 ml) after dissolving by heating, was stirred at room temperature for overnight. The TLC analysis showed the absence of thiocolchicoside in the reaction mixture, (one small drop of reaction mixture was diluted with MeOH (0.5 ml) and applied to a TLC plate and run in solvent system A). The reaction mixture was poured on ice, adjusted to pH 5 by the addition of 15% aqueous NaOH solution, followed by several extractions with CH2Cl2 (4×25 ml). The combined organic layers were dried (Na2SO4) and evaporated to afford a residue, which was crystallized with acetone to afford 3-demethylthiocolchicine as a yellow solid (1.5 g, 93%), mp 316° C.; [α]D25 =-251° (c 0.21, CHCl3); IR (CHCl3) cm-1 ; 3440 (OH); CIMS: m/e 402 (M+ +1); Anal. Calcd. for C21H23NO5S: C, 62.82; H, 5.77; N, 3.48; S, 7.98. Found C, 63.09; H, 5.86; N, 3.26; S, 8.25%.
