SYNTHESIS DIRECTED TOWARDS PUTATIVE ADVANCED INTERMEDIATES IN SARUBICIN-A BIOSYNTHESIS

3,6-Dihydroxyanthranilamide, 5, and its 5-propyl derivative, 15, were synthesized. The former was found to be very unstable, but the later was stable and could be reversibly oxidized to the analogous quinone. 3,6-Dimethoxyanthranilamide was protected as an acetone acetaminal and formylated at C-5 to give 18. A hetero-Diels-Alder reaction with Danishefsky's diene and 18 was effected with the aid of sonication and ZnCl2, yielding a model, 20, for a putative C-glycoside intermediate in the biosynthesis of sarubicin A, 1. However, when 18 and the triethylsiloxydiene derived from 3-penten-2-one were treated under the same conditions no reaction occurred, while p-dimethylaminobenzaldehyde only gave an aldol product 23.