Reaction Steps
To a solution of curcumin (300 mg, 0.81 mmol), cis-docosahexaenoic acid (275 mg, 0.83 mmol) and catalytic amount of 4-(dimethylamino)pyridine in DCM (10 mL) was added a solution of N,N′-dicyclohexylcarbodiimide (252 mg, 1.2 mmol) in DCM (5 mL) for 5 min at ice cold temperature. The mixture was stirred at rt for 16 h and diluted with water. DCM layer was separated and the aqueous layer was extracted with DCM (3×100 mL). The combined DCM 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 mixture (90:10) as an eluent to give the product as oil (250 mg, 45%). IR (neat) νmax 3015, 2960, 2930, 1761, 1631, 1593, 1269, 1120, 1031, 972 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 (12H, m, H-4′″, 5′″, 7′″, 8′″, 10′″, 11′″, 13′″, 14′″, 16′″, 17′″, 19′″, 20′″), 3.95 (3H, s, Ar—OCH3), 3.87 (3H, s, Ar—OCH3), 2.84-2.86 (10H, m, H-6′″, 9′″, 12′″, 15′″, 18′″), 2.58-2.66 (2H, m, H-2″), 2.22-2.23 (2H, m, H-21″), 2.05-2.09 (2H, m, H-3′″), 0.97 (3H, t, J=7.4 Hz, H-22′″); LCMS (ESI, negative ion mode): m/z 677 (M-H)−.
