Absolute configuration of azaphilones from KB9 and solvent effects on their keto and enol forms.

fermented rice, also known as red yeast rice, exhibits a broad spectrum of biological activities due to its chemical constituents, such as monacolins and azaphilone pigments. Here, we cultured KB9 in a liquid malt medium instead of on rice as a carbon source. Eleven known compounds (-) containing azaphilones and their early intermediate were isolated and identified. However, this was the first time that angular tricyclic azaphilones, monasfluols A () and B (), acetyl-monasfluol A () and monasfluore A (), were isolated from this species. Interestingly, all isolated tricyclic azaphilones existed exclusively in enol form in CDOD, as evidenced by NMR spectroscopy. The absolute configuration of compounds - was also first experimentally identified based on ECD spectroscopy combined with conformational analyses using computational techniques. The assigned stereochemistry of azaphilones in this work provides essential structural information that will benefit future biological and pharmaceutical investigations.