Ishigadine A, a new canthin-6-one alkaloid from an Okinawan marine sponge Hyrtios sp

A new indole alkaloid with the canthin-6-one skeleton, ishigadine A, has been isolated from an Okinawan marine sponge Hyrtios sp. The structure of ishigadine A was elucidated on the basis of spectroscopic analyses. Ishigadine A is a new canthin-6-one alkaloid possessing a hydroxy group, a 1,3-dimethyl-4-methylthioimidazolium, and a 1-propylguanidine. Ishigadine A is the third canthin-6-one alkaloid from sponges. Ishigadine A might be generated from l -arginine, l -histidine, and l -tryptophan. Ishigadine A exhibited moderate cytotoxicity against L1210 murine leukemia cells.