Nitrogen Oxide Inhibitory Trimeric and Dimeric Carbazole Alkaloids from Murraya tetramera

Two new structurally unique trimeric carbazole alkaloids, murratrines A and B (1,2), and 11 new carbazole dimers, murradines A-K (3-13), and four known analogues (14-17) were isolated from the leaves and stems of Murraya tetramera. The structures and relative configurations of 1-13 were elucidated on the basis of comprehensive 1D and 2D NMR spectroscopy, high-resolution mass spectrometry; and electronic circular dichroism (ECD) data analysis. Murratrines A and B (1,2) both contain an unprecedented carbazole trimeric skeleton, and murradines A and D (3,6) are the first natural C-1-C-3'-methyl-linked and C-6-C-3'-methyl-linked dimeric carbazole alkaloids, respectively. Compounds 4, 10, 14, 15, and 17 exhibited inhibition of nitric oxide production stimulated by lipopolysaccharide in BV-2 microglial cells with IC50 values in the range of 11.2-19.3 mu M.