Host: Division of Organic Chemistry, The Pharmaceutical Society of Japan
Caulersin, isolated in 1997 from the alga Caulerpa serrulata, is a member of bisindole alkaloids and has an extra seven-membered cyclic ring between the two indole rings incorporated directly with carbonyl group. Caulersin was synthesized by Molina, our group, and Bergman and the structure of the synthesized caulersin by Bergman was confirmed by X-ray diffraction study. However, 13C-NMR spectrum of the synthesized caulersin by Bergman is different from that of natural caulersin. We consider that the structure of caulersin is not correct and think out three isomers A–C of caulersin to decide the real structure. Three isomers A–C were synthesized by reaction of indole-2,3-dicarboxylic anhydride with methyl indole-2-acetate or methyl indole-3-acetate. Spectral data of the isomers A–C are not same as those of natural caulersin and the structure of caulersin is yet unclear.
