Structure Determination of Flavonoids Isolating from Nymphaea tetragona using NMR spectra and spin simulations

Abstract

Nymphaea tetragona, also known as waterlilies, is aquatic plant in the family of Nymphaeceae. Three flavonoids(3, 4, and 5) and one mixed flavonoids were separated from this plant. The mixed flavonoid consisted of two flavonoids; a well-known quercetin(1) and a new natural flavonoid(2). The latter also has two chiral centers and their configurations were established by ROESY experiment. Two glycoflavonoids were determined as isoquercetin and quercetin-3 -O-beta-xyropyranosyl-( 1 -> 2)-beta-galacto-pyroside. The H-1 NMR spectra for 4 and 5 dissoloved in DMSO-d(6) solvent showed resonance proximity and and severely overlap in the glycoside region, hindering the determination of the configurations of the stereogenic centers of the sugar moieties. This problem was solved through the spin simulation. Here, the exact NMR parameters for the sugar moieties of 4 and 5 were listed.