N–N‐Coupled Indolo‐sesquiterpene Atropo‐Diastereomers from a Marine‐Derived Actinomycete

Abstract

Abstract Four new indolo‐sesquiterpenes – dixiamycins A ( 1 ) and B ( 2 ), oxiamycin ( 3 ), and chloroxiamycin ( 4 ) – were isolated from a marine‐derived Actinomycete and characterized, together with the known compound xiamycin A ( 5 ). Dixiamycins A ( 1 ) and B ( 2 ) are the first examples of atropisomerism of naturally occurring N‐N‐coupled atropo‐diastereomers, with a dimeric indolo‐sesquiterpene skeleton and a stereogenic N‐N axis between sp 3 ‐hybridized nitrogen atoms. Solution TDDFT ECD calculations were utilized to ascertain the axial chirality of 1 and 2 , and rotational barriers and transitions states of the inversion were calculated. Oxiamycin ( 3 ) contains a seven‐membered 2,3,4,5‐tetrahydrooxepine ring. The two dimeric compounds 1 and 2 showed better antibacterial activities than the monomers 3 – 5 .