Recently, a number of interesiting marine natural products with novel structures and biological functions have been found, usually in very small quantities. Accordingly, our great efforts have been focused on total syntheses of these compounds in gram scale, as follows.
1)Synthetic studies on pyrroloquinoline alkaloids
A new class of pyrroloquinoline alkaloids have been isolated as metabolites of the New Zealand, Okinawan and Fijian sponges. They show remarkable antitumor activities and particularly possess potent inhibitory activities against the function of topoisomerase II.We successfully synthesized discorhabdin C, batzelline C, isobatzelline C, makaluvamines A, B, C and D.Some of their synthetic intermediates were also proved to have antitumor activities.
2)Synthetic studies on novel pyrone-metabolites of some marine organisms
Peroniatriols and ilikonapyrone are considered to be defensive substances of some kinds of marine molluscs. We developed new systhetic methodology to construct
a fully substituted gamma-pyrone ring, and determined the absolute configurations of these pyrones by means of the above mentioned method.
3)Synthetic studies on bryostatins
Bryostatins, the highly oxygenated macrolides are one of the most attractive marine natural products for their therapeutically antineoplastic activities. Our considerable efforts have been made for syntheses of bryostatin 11 in gram scale. And we could synthesize two main moieties which include all of carbon atoms of bryostatin 11. Further synthetic study on this macrolide is in progress.
4)Synthetic studies on bioactive substances produced by marine sponges and sea hears
We had already synthesized bastadins, aerothionin and related marine natural products, all of which have an interesting spiroisoxazol ring and show antibacterial activities. We further attempt to synthesize psammaplysin which has been isolated as the metabolite of sea hare. We also developed a new synthetic method to construct trans-hydroazulenes, using electrochemical technique, from which a number of marine natural products will be derived. Less