Two new Monascus metabolites with strong blue fluorescence isolated from red yeast rice.

Red yeast rice obtained as cultures of Monascus AS3.4444 on rice was extracted and analyzed by high-performance liquid chromatography (HPLC). Two new Monascus metabolites with similar fluorescence spectra (λ ex = 396 nm, λ em = 460 nm) and UV absorption spectra (λ max = 386 nm) were detected. They were isolated by rechromatography on a silica gel column and semipreparative HPLC, and two strong blue fluorescent compounds were obtained. Their structures were elucidated by electrospray ionization mass spectrometry (ESI−MS), electrospray ionization tandem mass spectrometry (ESI−MS/MS), intensive ESI−MS, and nuclear magnetic resonance spectroscopy ( 1H NMR, 13C NMR, COSY, and HMBC) studies. High-resolution mass spectrometry indicated the molecular formulas C 21H 24O 5 and C 23H 28O 5. The two new compounds, named monasfluore A and monasfluore B, respectively, contain a alkyl side chain, γ-lactone, and propenyl group, whereas the more lipophilic compound, monasfluore B, is a higher homologue of monasfluore A, w...