Isolation and structural characterization of two new metabolites from monascus.

Two new pale yellow metabolites have been isolated from commercially available Chinese food additive Red Monascus Pigment and from Monascus ruber culture broth. They were isolated by successive TLC and semipreparative HPLC. Their structural characterization was elucidated by a variety of spectroscopic techniques (UV, IR, NMR) and mass spectrometry. These two new metabolites present numerous similarities with monascorubrin and rubropunctatin, differing in their structure only by the absence of the lactone ring. High-resolution mass spectrometry indicated the molecular formulas C(20)H(26)O(4) and C(22)H(30)O(4). The new compounds, named monarubrin and rubropunctin, contain a propenyl group on a pyrone ring, an alkyl side chain, but no gamma-lactone ring. The new metabolites have the property of producing strong blue fluorescence at 340 nm.