Physicochemical screening identified a new nanaomycin analog, nanaomycin H, which was isolated from a culture broth of Streptomyces rosa subsp. notoensis OS-3966. This microorganism is already known to produce seven nanaomycin compounds, (nanaomycin A to G). Structural elucidation of nanaomycin H showed it to be a pyranonaphthoquinone with a mycothiol moiety. A N-acetylcysteine S-conjugate of nanaomycin H, without oc-glucosamine linked to myo-inositol moiety, mercapturic acid derivative, was also detected in the same culture broth. Mercapturic acid derivatives of secondary metabolites are known to be produced for xenobiotic metabolism outside microbial cells. Mycothiol acts as a detoxifier to help prevent cell damage from factors such as oxidative stress. The production of O-2(-). generated by reduction of nanaomycin A is correlated with antibacterial activity. Mycothiol-containing nanaomycin H proved to be markedly decreased in O-2(-). and did not express any notable antimicrobial activity. It is suggested that nanaomycin H is produced in the detoxification process. (C) 2017, The Society for Biotechnology, Japan. All rights reserved.