Combination of 1 H and 13 C NMR for quantitative analysis of the orange pigments produced by Monascus kaoliang KB9.

Two orange pigments, rubropunctatin ( 1 ) and monascorubrin ( 2 ), along with the yellow pigments, monascin ( 3 ) and ankaflavin ( 4 ), were isolated from M. kaoliang KB9-fermented rice, also known as red yeast rice. The orange pigments exhibit a broad spectrum of biological activities and appeared to be the major components of this fermented rice. In this work, quantitative 1 H NMR (qHNMR) and 13 C NMR experiments were used to determine the amounts of the two orange pigments in a crude extract in which most of the 1 H NMR signals of the two compounds were indistinguishable. The quantitative values obtained by NMR techniques were found to be similar to those obtained by HPLC. Thus, the combined qHNMR with 13 C experiment described in this work could be further developed to quantifying Monascus pigments or other invaluable natural products when qHNMR alone is insufficient for quantitative analysis.