Drug Leads Derived from Japanese Marine Organisms.

Many natural products with extraordinary chemical structures and brilliant biological activities have been obtained from marine organisms. We have investigated such fascinating bioactive molecules, exemplified by the potent marine toxin palytoxin and the antitumor molecule halichondrin B, which has been developed as the anticancer drug Halaven®, to explore novel frontiers in organic chemistry and bioscience. Working within the traditional discipline, we have sought to acquire a deeper understanding of biological phenomena. We introduce here our major work along with up-todate topics. We isolated yoshinone A from marine cyanobacteria and completed a gram-scale synthesis. Yoshinone A is a novel polyketide that inhibited the differentiation of 3T3-L1 cells into adipocytes without significant cytotoxicity. The detailed mechanisms of action will be elucidated via further experiments in vitro and in vivo. In this study, we explore the true producers of okadaic acid and halichondrin B by immunostaining of Halichondria okadai with an antibody that was prepared using these natural products as an antigen. We will analyze isolated symbionts and reveal biosynthetic pathways.