Production and identification of N-glucosylrubropunctamine and N-glucosylmonascorubramine from Monascus ruber and occurrence of electron donor-acceptor complexes in these red pigments

The filamentous fungus Monascus ruber produces water-soluble red pigments in a submerged culture when grown in a chemically defined medium containing glucose as a carbon source and monosodium glutamate as a nitrogen source, Two new molecules with polyketide structures, N-glucosylrubropunctamine and N-glucosylmonascorubramine, constituting under some conditions 10% of the total extracellular coloring matter when glucose as a carbon source was in excess (20 g/liter), were isolated and structurally characterized by high-pressure liquid chromatography, Dionex methods, H-1 and C-13 nuclear magnetic resonance spectroscopy, and mass spectrometry, The occurrence of the electron donor-acceptor complex effect was demonstrated by UV spectroscopy, polarography, and thin-layer voltammetry, The use of n-butanol as an extraction solvent stabilized the pigments against the effects of daylight for several months, promoting the stability of this type of complex.