Talosins A and B: new isoflavonol glycosides with potent antifungal activity from Kitasatospora kifunensis MJM341. I. Taxonomy, fermentation, isolation, and biological activities.

In our screening program for new antifungal agents from microbial secondary metabolites, we isolated two new isoflavonol glycosides, genistein 7-alpha-L-6-deoxy-talopyranoside (talosin A) and genistein 4',7-di-alpha-L-6-deoxy-talopyranoside (talosin B), from the culture broth of Kitasatospora kifunensis MJM341. The talosins exhibited strong antifungal activity against Candida albicans, Aspergillus niger and Cryptococcus neoformans with minimal inhibitory concentrations (MIC) in the range of 3- 15 microg/ml while genistein and genistein-7-glucopyranoside did not show antifungal activity at 100 microg/ml. These talosins are the first isoflavonol glycosides with a 6-deoxy-talose sugar component and they may be useful as antifungal agents with low toxicity because of no visible cytotoxicity against the human hepatic HepG2 cell.