Reaction Steps
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 (1.3 g) in pyridine (10 ml) DMAP (0.57 g) was added followed by the crude reaction mixture (anhydride formation). The reaction mixture was stirred at reflux temperature for about 12 hours. After completion of the reaction (monitored by TLC), the mixture was cooled to room temperature, diluted with EtOAc, washed with dil HCl, water, followed by brine and dried over Na2SO4, and concentrated under reduced pressure. The crude reaction mixture was purified by column chromatography using hexane and ethyl acetate mixtures as an eluent to afford the title compound (300 mg, 15% yield). 1H NMR (300 MHz, CDCl3): δ 7.37-7.33 (5H, m), 5.16 (2H, m), 4.73 (1H, s), 4.61 (1H, s), 4.45-4.36 (1H, m), 3.65-3.6 (1H, m), 3.1-2.90 (1H, m), 2.85-2.6 (3H, m), 2.4 (1H, m), 2.3-1.9 (5H, m), 1.8-1.3 (17H, m), 1.26 (4H, m), 1.24 (3H, s), 1.22 (2H, m), 1.16 (3H, s), 1.14 (3H, s), 1.00 (2H, m), 0.8 (6H, s); Mass: [M+Na]+ 723 (15%); IR (KBr, cm−1): 3427, 2953, 17330, 1730, 1459, 1376, 1277, 1236, 1187, 1107, 1034, 940, 882.
