Conformational analysis of the biflavanoid GB2 and a polyhydroxylated flavanone-chromone of Cratoxylum neriifolium

Abstract Three compounds, namely the interesting biflavanonol GB-2 (naringenin I-3, II-8-dihydroquercetin, 1), I-4′,I-5,II-5,I-7,II-7-pentahydroxyflavanone(I-3,II-8)chromone [naringenin-(3→8) 5,7-dihydroxychromone, 2] and stigmasterol, have been isolated from the leaves of CRATOXYLUM NERIIFOLIUM Kurz. Compounds 1 and 2 show rotameric behavior due to the presence of a single bond between the highly substituted flavanone and flavanonol part and the flavanone and chromone part, respectively. Complete NMR spectral assignments of 1 and 2 have been done at 27 °C and 90 °C for the first time followed by a study of conformational behavior at room temperature by ROESY.