(+)- and (−)-actinoxocine, and actinaphthorans A–B, C-ring expansion and cleavage angucyclinones from a marine-derived Streptomyces sp.

(+)- and (-)-actinoxocine (1), a pair of enantiomeric C-ring expansion angucyclinones, featuring a unique epoxybenzo[f]naphtho[1,8-bc]oxocine carbon skeleton, and two unusual C-ring cleavage analogues, actinaphthorans A-B (2-3), were isolated from a marine-derived Streptomyces sp. Their structures and absolute configurations were assigned by spectroscopic analysis, X-ray diffraction and CD calculations.