Reaction Steps
Ac2O (about 0.93 ml, 9.87 mmol) was added to a stirred solution of (1R,3aS,5aR,5bR,7aR,9S,11aR,11bR,13aR,13bR)-9-hydroxy-5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)icosahydro-1H-cyclopenta[a]chrysene-3a-carboxylic acid (Betulinic acid, about 0.3 g, 0.657 mmol) and DMAP (about 0.167 g, 1.32 mmol) in pyridine (about 15 ml) at about 0° C. then the reaction mixture was slowly warmed to room temperature and refluxed for about 24 hours. After completion of the reaction (monitored by TLC), the reaction mixture poured in to ice water and extracted with EtOAc and washed with water, brine and dried over Na2SO4, the solvent was evaporated and purified by silica gel column (100-200, elution 10% EtOAc in hexane) to afford title compound as a off white solid. Wt: 0.196 g; Yield: 59.8%; 1H NMR (300 MHZ, CDCl3): δ 4.74 (s, 1H), 4.61 (s, 1H), 4.50-4.44 (m, 1H), 3.02-2.97 (m, 1H), 3.01-2.12 (m, 2H), 2.04 (s, 3H), 1.99-1.92 (m, 2H), 1.69 (s, 3H), 1.68-1.57 (m, 6H), 1.56-1.32 (m, 10H), 1.31-1.01 (m, 5H), 0.97, 0.93 (2s, 6H), 0.85 (Brs, 9H); Mass: [M−1] 497 (100%); IR (KBr, cm−1): 3296, 2945, 1736, 1694, 1464, 1368, 1247, 1196, 1161, 1024, 980, 884, 777, 543; M.R: 283.7° C.-290.1° C.; HPLC: 97.17%.
