Peltogynoids contributing to discoloration in Peltogyne mexicana heartwood

Four new peltogynoid monomers (3, 7, 10, 11) and a new peltogynoid dimer (9) were isolated from the heartwood of Peltogyne mexiacana, along with six known compounds (1, 2, 4, 5, 6, 8). Among the known compounds, the absolute configurations of two flavanones (5, 6) were determined. The structures of the isolated compounds were determined using NMR and MALDI-TOF MS analysis. The discoloration of the methanol solutions of the isolated peltogynoids and flavanones was examined by exposing them to room light in the air. The methanol solutions of (+)-peltogynol (1) and (+)-mopanol (4) discolored to reddish and bluish purple, respectively. After discoloration, the b* values of these compounds decreased significantly from 12.1 to 19.1 to -0.7 and − 1.8, respectively. These precursors of pigment compounds 1 and 4 have a catechol moiety in the B ring, and a hetero-six-membered ring (D ring) connecting the B and C ring of flavan-3,4-diol via an oxyethylene bridge, which is similar to the structure of leucoanthocyanidin. These results led to the hypothesis that the metabolized pigment compounds have anthocyanidin-like structures with peltogyne skeleton.