Hyrtiosin, a novel pyridinium-conjugated indole derivative from vietnamese marine sponge hyrtios erectus

The present phytochemical investigation of methanol extract from Vietnamese marine sponge, Hyrtios erectus, resulted to the isolation and structure elucidation of five compounds consisting of a new pyridinium-conjugated indole derivative (hyrtiosin, 1), together with four known alkaloids identified as gramine (2), indole-3-carboxaldehyde (3), 3-(methoxymethyl)indole (4) and N-methylnicotinic acid or trigonelline (5). Chemical structures of isolated compounds were established using modern spectroscopic methods including NMR (¹H,¹³C, COSY, HSQC, HMBC), HR-ESIMS, UV and IR. Compound 1 is rare occurrence of natural products with an acetyl moiety linked to N-1. The isolated compounds were tested with inhibitory activity of NO production and growth of bacterial strains. Among them, only compound 1 displayed the weak inhibition of nitric oxide production with an IC₅₀ value of 38.2 μM, others unfortunately have no activity in both of assays. All of them are first report both of isolation, structural elucidation and bioactivities from specie H. erectus.