Isolation and structure elucidation of pyridinium-type metabolites from the sponge Agelas nakamurai

Chemical investigation of the Formosan marine sponge Agelas nakamurai led to the isolation of four pyridinium compounds (1-4). The structures were elucidated through comprehensive spectroscopic analysis, including 1D and 2D NMR and HRESIMS. Among these, agelapyridinium A (1) is a naturally undescribed 2,4-dimethyl-1-phenylethylpyridinium, while pyridinebetaine C (2) is a new 2,4-dimethylated sulfonate-containing pyridinium betaine. Additionally, the known metabolites pyridinebetaine A (3) and pyridinebetaine B (4) were identified for the first time from this organism. All isolated compounds were shown to be inactive in inhibiting the growth of the few tested cancer cell lines and bacteria in the conducted bioassays. The putative biosynthetic pathways for the isolated pyridinium compounds were also proposed herein.