Hyrtiosin, a novel pyridinium-conjugated indole derivative from vietnamese marine sponge <i>hyrtios erectus</i>

The present phytochemical investigation of methanol extract from Vietnamese marine sponge, <i>Hyrtios erectus</i>, resulted to the isolation and structure elucidation of five compounds consisting of a new pyridinium-conjugated indole derivative (hyrtiosin, <b>1</b>), together with four known alkaloids identified as gramine (<b>2</b>), indole-3-carboxaldehyde (<b>3</b>), 3-(methoxymethyl)indole (<b>4</b>) and <i>N</i>-methylnicotinic acid or trigonelline (<b>5</b>). Chemical structures of isolated compounds were established using modern spectroscopic methods including NMR (¹H,¹³C, COSY, HSQC, HMBC), HR-ESIMS, UV and IR. Compound <b>1</b> is rare occurrence of natural products with an acetyl moiety linked to <i>N</i>-1. The isolated compounds were tested with inhibitory activity of NO production and growth of bacterial strains. Among them, only compound <b>1</b> 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 <i>H. erectus.</i>