SYNTHESIS OF PUTATIVE INTERMEDIATES IN THE BIOSYNTHESIS OF THE KINAMYCIN ANTIBIOTICS - TOTAL SYNTHESIS OF PHENANTHROVIRIDIN AGLYCON AND RELATED-COMPOUNDS

Phenanthroviridin aglycon, 14, recently isolated from Streptomyces viridiochromogenes DSM 3972, and the corresponding pyridone 10 have been synthesized from the common intermediate (bromoaryl)naphthamide 42. This was prepared by condensation of a (trimethylsilyl)ethyl (bromoaryl)cinnamate 36 and a methoxy-substituted cyanophthalide anion 15, providing the ABD rings of the target benzo[b]phenanthridine skeleton. The aglycon 14 was obtained by a sequence of metal-halogen exchange and formylation, Hofmann rearrangement, cyclization, and deprotection. The pyridone was obtained by Hofmann rearrangement, metal-halogen exchange, cyclization, and deprotection. In addition, a route to cinnamate 36 via coumarin 49 was developed which would allow selective protection of the 1-hydroxyl group for synthesis of glycosidic analogues of phenanthroviridin, 13. The methodology developed is useful for preparation of 10, 14, and analogues specifically labeled at C-5 for study of biosynthesis of the kinamycin antibiotics.