Citridones, new potentiators of antifungal miconazole activity, produced by Penicillium sp FKI-1938I.: Taxonomy, fermentation, isolation and biological properties

New phenylfuropyridinones and related compounds, designated citridones A, B, B' and C, were isolated along with known CJ-16,173, from the culture broth of Penicillium sp. FKI-1938 by solvent extraction, silica gel column chromatography and HPLC. Citridones (75 mu M) potentiate the miconazole activity against Candida albicans, decreasing the IC50 value of miconazole from 14.5 nM to 3.5 similar to 6.3 nM.