Chemistry of Structurally Confused Kinamycins

Abstract

Kinamycin antibiotics, strongly active against gram-positive bacteria, were isolated from the culture broth of Streptomyces murayamaensis. Their structures were firstly determined to be a benzo[b]carbazoloquinone skeleton with N-cyanamide [N-C≡N] moiety. After that, prekinamycin was isolated from the same organism as a biosynthetic precursor and the same 6-6-5-6 ring system was also proposed for the structure. But problems still remained on the determination of substituent pattern at N-cyanamide moiety by spectroscopic means. Recently, the structures of kinamycins and prekinamycin were revised to be a benzo[b]fluorene skeleton with diazoalkane moiety [C--N + ≡ N]. However, a synthetic compound with the revised structure for prekinamycin was found to be different from natural prekinamycin, instead an isomeric benzo[a]fluorene skeleton, a 6-5-6-6 ring system was proposed for the natural product, which was newly named as isoprekinamycin. Herein the chemistry of kinamycins and their related compounds with structural confusions is reviewed, especially focused on the history of structural determination and recent synthetic studies.