Dandamycin and chandrananimycin E, benzoxazines from Streptomyces griseus

Two new benzoxazines were isolated from Streptomyces griseus (HKI 0545) and assigned as chandrananimycin E (1) and dandamycin (2). Although a number of phenoxazinone-type compounds have been reported from nature, phenoxazines are rarer, and carbon substitution at N-10 such as in 1 is unprecedented. The cyclopentene-containing ring structure of dandamycin (2) is also unique. Chandrananimycin E (1) was found to possess moderate antiproliferative activity against HUVEC cells (GI₅₀ 35.3 μM) and weak cytotoxic activity towards HeLa cells (CC₅₀ 56.9 μM). Dandamycin showed neither antiproliferative activity nor cytotoxicity towards these cell lines. Structure activity comparisons with phenoxazinones isolated from S. griseus HKI 0545 suggested that the alteration of the core ring systems in 1 and 2 diminishes their activity. Natural products 1 and 2 are interesting additions to the rich secondary metabolome of S. griseus and constitute an important addition to the body of knowledge on phenoxazinone-derived metabolites.