New monascus metabolites with a pyridine structure in red fermented rice.

Monascus purpureus produces several hitherto unknown compounds in addition to pigments and the mycotoxin citrinin. In red fermented rice (angkak, red koji) obtained as cultures of M. purpureus DSM1379 and DSM1603, we detected two compounds with identical UV absorption spectra and maxima at 306-307 nm. They were isolated by HPLC, and their structures were elucidated by intensive MS and NMR studies. Monascopyridine A (3) contains a gamma-lactone, propenyl group, hexanoyl side chain, and a pyridine ring, whereas the more lipophilic compound, monascopyridine B, is a higher homologue of monascopyridine A with the more lipophilic octanoyl instead of the hexanoyl side chain. This is the first report of Monascus metabolites with a pyridine ring.