Preparation of Alkyl-Substituted Indoles in the Benzene Portion. Part 13. Enantiospecific Synthesis of Mitosene Analogues Related to FR 900482 and FR 66979.
Preparation of Alkyl-Substituted Indoles in the Benzene Portion. Part 13. Enantiospecific Synthesis of Mitosene Analogues Related to FR 900482 and FR 66979.
Preparation of Alkyl-Substituted Indoles in the Benzene Portion. Part 13. Enantiospecific Synthesis of Mitosene Analogues Related to FR 900482 and FR 66979.
An acid-catalyzed indole formation reaction previously reported by us was successfully applied to the preparation of variously substituted 4-hydroxy-1H-indoles 11a-g having carbon and/or heteroatom substituents at the benzene portion of the indole ring, using as substrates 3-(4, 4-dialkoxy-1-oxobutyl)-1H-pyrroles 10a-g, which are readily available from simple pyrroles in several steps. Employing one of these indoles, 11g, as a starting intermediate, an enantiospecific synthesis of the mitosene analogues 8, 9a and 9b related to antitumor antibiotics FR 900482 (1) and FR 66979 (2) was achieved by i) condensation of 20 with a chiral aldehyde 21, ii) transformation of 22a and 22b into the tricyclic compounds 29a and 29b, iii) introduction of the additional one-carbon unit as a formyl group, iv) formation of the aziridine ring, and v) removal of the benzyl protecting group. Elimination of the tert-butyloxycarbonyl group was also examined to provide the basis for a future project to synthesize 5a, the cross-linkage product of 2 and DNA.