Alkaloids Isolated From the Gastropod Reishia clavigera : Their Antibacterial and Cytotoxic Activities

Reishia clavigera , an edible marine gastropod consumed in Asia and used in traditional medicine, was investigated for its secondary metabolite content. Despite its widespread consumption and ethnomedicinal use, no comprehensive study has examined the secondary metabolites from whole‐body extracts. Sequential chromatographic fractionation of the whole‐body extract yielded six alkaloids whose structures were elucidated by NMR spectroscopy and HRMS analysis. Six alkaloids ( 1 – 6 ), including four indole derivatives such as homarine ( 2 ), tyrindoxyl sulfate ( 3 ), and an inseparable mixture of oxazinins 1 and 2 ( 5 and 6 ), were obtained and identified. Notably, a previously undescribed sulfoxide derivative ( 4 ) of tyrindoxyl sulfate was also characterized. The growth inhibitory activities of isolated compounds against human leukemia (K562) and 6 pathogenic bacterial cell lines were measured. A mixture of oxazinins 1 and 2 ( 5 and 6 ) exhibited moderate cytotoxicity against K562 cells (IC 50 = 23.0 μg/mL), while tyrindoxyl sulfate derivatives ( 3 and 4 ) showed promising activity against Staphylococcus aureus (MIC = 4.0 and 2.0 μg/mL, respectively). This study represents the first report on the secondary metabolites from the entire body of R. clavigera . Considering that R. clavigera is one of the edible mollusks in several Asian countries and used as folk medicine in some regions, in‐depth studies regarding the biological activities and toxicities of the compounds discovered in this study should be followed.