Structural characterization and antimicrobial activities of two Monascus orange pigment derived pigments

In this study, two derivative pigments RA and RB were obtained by the reaction of Monascus orange pigment-rubropunctatin (O1) and monascorubrin (O2) with ethanolamine, respectively. The two derivatives were separated and purified by preparative thin layer chromatography (PTLC). The molecular weight, molecular formula and molecular structure of two derivative pigments RA and RB were analyzed by HPLC, LC-MS and nuclear magnetic resonance (NMR) techniques, and the antimicrobial activities of orange pigments and two derivative pigments were evaluated by the inhibition zone method. The results showed that the purity of RA and RB was more than 95%. The molecular mass of RA and RB were 397 Da and 425 Da, respectively, and the molecular formulas were C₂₃H₂₉NO₅ and C₂₅H₃₁NO₅, respectively. The molecular structures of RA and RB analyzed by NMR were erythromonastin (O1) and erythromonastin (O2) derived pigments. The results of antibacterial activities of orange pigments and two derived pigments showed that orange pigments 1 mg/ml and RB all had antimicrobial activity against Staphylococcus aureus ATCC 25923 and Listeria monocytogenes ATCC 19115, while RA did not show antimicrobial activity under the same conditions. The amination reaction of monascorubin (O2) with ethanolamine provided an effective way for the directional production of Monascus pigment RB with high antimicrobial activity.