Reaction Steps
To a solution of curcumin (300 mg, 0.81 mmol), cis-eicosapentaenoic acid (250 mg, 0.83 mmol) and catalytic amount of 4-(dimethylamino)pyridine in dichloromethane (10 mL) was added a solution of N,N′-dicyclohexylcarbodiimide (252 mg, 1.2 mmol) in dichloromethane (5 mL) for 5 min at ice cold temperature. The mixture was stirred at rt for 16 h and diluted with water. The dichloromethane layer was separated and the aqueous layer was extracted with dichloromethane (3×100 mL). The combined dichloromethane layer was washed with water, brine and dried over sodium sulfate. The solution was filtered and the residue was chromatographed over silica gel column using hexane-ethyl acetate (90:10) mixture as an eluent to give the product as an oil (235 mg, 44%). IR (neat) νmax 3013, 2961, 2929, 1762, 1630, 1593, 1268, 1123, 1032, 970 cm−1; 1H NMR (CDCl3) δ 7.61 (1H, d, J=16.0 Hz, H-1), 7.60 (1H, d, J=15.6 Hz, H-7), 7.03-7.16 (5H, m, H-2′, 2″, 5′, 6′, 6″), 6.93 (1H, d, J=8.4 Hz, H-5″), 6.55 (1H, d, J=16 Hz, H-2), 6.49 (1H, d, J=16 Hz, H-6), 5.89 (1H, br s, Ar—OH), 5.83 (1H, s, H-4), 5.38-5.39 (10H, m, H-5′″, 6′″, 8′″, 9′″, 11′″, 12′″, 14′″, 15′″, 17′″, 18′″), 3.95 (3H, s, Ar—OCH3), 3.87 (3H, s, Ar—OCH3), 2.84-2.86 (8H, m, H-7′″, 10′″, 13′″, 16′″), 2.58-2.66 (2H, m, H-2′″), 2.22-2.23 (2H, m, H-19′″), 2.05-2.09 (2H, m, H-4′″), 1.82-187 (2H, m, H-3′″), 0.97 (3H, t, J=7.4 Hz, H-20′″); LCMS (ESI, negative ion mode): m/z 651 (M-H)−.
