A new development to the synthesis of biologically active natural product by the electrocyclic reaction of aza 6π-electron system

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(1)Synthetic studies of poly-functionalized carbazole alkaloid possessing neuronal cell protecting activitySyntheses of racemic and chiral desprenylcarquinostatin have been established. A suitable 1,3-dioxygenated 3-methylcarbazole was prepared by the allene-mediated electrocyclic reaction involving the indole 2,3-bond. The 1-(2-hydroxyprpyl)carbazole was synthesized from 1-hydroxycarbazole was subjected to the lipase-catalyzed enantioselective acetylation to give the chiral acetate and the alcohol, respectively. Hydrolysis of the chiral acetate gave the another chiral alcohol. Absolute stereochemistries of (+)- and (-)-alcohols were determined as S- and R- configurations, respectively, by the modified Moscher method. The (R)-(-)-acetate was oxidized by selenic anhydride to produce (R)-(-)- despenylcarquinostatin. Racemic desprenylcarquinostatin was also obtained from racemic acetate in a simila way. (To be published.)(2)Synthetic studies of pentacyclic calothrixins A and B possessing … More antimalarial and antitumor activitiesA new total synthesis of calothrixin B was achieved. A suitable 2-(2-nitrophenyl)-4-methoxymethyloxy-3-methylcarbazole was synthesized by the allene-mediated electrocyclic reaction involving the indole 2,3-bond. Oxidation of 3-methylcarbazole derivative with DDQ gave the 3-formylcarbazole along with the cleavage of methoxymethyl group. Reduction of nitro group on the phenyl ring with Pd-C and H^2 produced the pentacyclic indolophenanthridine, which was oxidized by CAN to provide calothrixin E. (To be published.)(3)Synthetic studies of 5-methylindole-4,7-quinone and veiutamineA total synthesis of 5-methylindole-4,7-quinone was completed. A suitable indole framework, N-benzyl-4-methoxy-5-methylindole-2-carboxylic acid, was synthesized by-the allene-mediated electrocyclic reaction involving the pyrrole 2,3-bond. The expected 5-methylindole-4,7-quinone was obtained in seven steps. However, The data of this compound was not identical with those of natural product reported by Fukuyama group. (Published) Furthermore, 6-methylindole-4,7-quinone was also synthesized in a similar methodology. (To be published.)A synthesis of veiutamine was attempted by the allene-mediated electrocyclic reaction. An appropriate indole framework could be synthesized. Conversion of indole framework into a tricyclic indoloiminoquinone ring is now under investigation. Less