Racemic xanthine and dihydroxydopamine conjugates from Cyclopelta parva and their COX-2 inhibitory activity

Seven new compounds including three pairs of enantiomeric xanthine analogues (1-3), a pair of enantiomeric hypoxanthine analogue (4), and three pairs of enantiomeric N-acetyldopamine dimers (6-8), together with a known one (5) were isolated from the insect Cyclopelta parva. Their structures including absolute configurations were assigned by using spectroscopic and computational methods. Chiral HPLC was used to separate racemic 1-8. Biological evaluation found that 6b and 7a are potent COX-2 inhibitory agents with IC₅₀ values at 385.2 nM and 868.8 nM respectively.