Reaction Steps
Diethyl chlorophosphate (0.507 g; 2.94 mM) was added to a solution of monic acid A (0.982 g; 2.94 mM) and triethylamine (0.412 ml; 2.94 mM) in dry tetrahydrofuran (50 ml). This solution was stirred at room temperature for three hours, under a nitrogen atmosphere. A solution of 8-methoxycarbonyloctylammonium chloride (0.65 g; 2.94 mM) and triethylamine (0.412 ml; 2.94 mM) in aqueous tetrahydrofuran (10 ml) was then added and the reaction mixture stirred for a further sixteen hours at room temperature. The solvent was then removed at reduced pressure and the residue partitioned between ethyl acetate and saturated sodium bicarbonate solution. The organic layer was washed with brine, dried over anhydrous magnesium sulphate and the solvent removed to yield the crude amide as a yellow oil. The product was purified by preparative thin layer chromatography on four 20×20×20×0.2 cm silica plates, eluting with 12% methanol/chloroform. The major band afforded the pure 8-methoxycarbonyloctylamide of monic acid A as a colourless oil. (0.610 g; 40%), [α]D20 -0.74° (c, 1.0 CHCl3), λmax (EtOH) 223 nm (εm 14,130); νmax (CHBr3) 3350, 1780, 1660 and 1630 cm-1 ; δH (CDCl3) 5.93 (1H, broad t, (NH), 5.62 (1H, s, CH=C), 3.65 (3H, s, CO2CH3), 2.13 (3H, s, CH3 -15), 1.30 (s, methylene envelope), 1.20 (3H, d, J 6.0 Hz, CH3 -14), 0.92 (3H, d, J 7.0 Hz, CH3 -17); δC (CDCl3) 174.4, 167.6, 150.3, 120.4, 75.1, 70.8, 70.5, 68.9, 65.5, 61.0, 55.7, 51.5, 42.7, 39.8, 39.4, 34.1, 31.8, 29.6, 29.1, 27.0, 24.9, 20.8, 18.7, 12.6, m/e 513 (M+) 482, 366, 269, 227, 188, 172, 156, 11, 83.
