Inhibitory effects of gossypol-related compounds on growth of Aspergillus flavus

The objective of this study was to test a series of gossypol-related compounds for growth inhibition against Aspergillus flavus.

A series of chiral and achiral gossypol derivatives, some natural products of the cotton plant and others prepared by synthesis from gossypol, were incorporated into agar plates to follow the rate of A. flavus isolate AF13 colony growth. All tested compounds exhibited some growth inhibition against this organism. The synthetic compounds, gossypolone and apogossypolone, exhibited greater activity than either racemic or chiral gossypol. Methylated derivatives (i.e. 6-methoxy and 6,6'-dimethoxy derivatives) generally exhibited less activity than the nonmethylated parent compounds. The (-)-optical form of gossypol was found to be slightly more active than the (+)-optical form, and this trend was observed regardless of the presence of methoxy groups at the 6-position. Growth inhibition of gossypolone and apogossypolone was concentration dependent. For gossypolone, the 50% effective dose was 90 μg ml⁻¹ of medium (165 μmol l⁻¹). For apogossypolone, the most active compound in the study, the 50% effective dose was 19 μg ml⁻¹ (38·7 μmol l⁻¹). The presence of gossypol-related terpenoids appeared to stimulate production of A. flavus sclerotia, although replicate variability was so large that it was not possible to determine a significant correlation between the mass of sclerotia formed and compound growth inhibition.

The quinone derivatives of gossypol, gossypolone and apogossypolone demonstrated significant fungal growth inhibitory activity against A. flavus.

These gossypol derivatives may provide a new class of fungicide for use against the mycotoxigenic fungus A. flavus.