Theoretical Calculation of Electronic CircularDichroism on a Hexahydroxydiphenoyl-Containing Flavanone Glycoside

Abstract

Theoretical calculation of electronic circular dichroism (ECD) of a hexahydroxydiphenoyl (HHDP)-containing flavanone glycoside, mattucinol-7-O-[4″,6″-O-(S)-hexahydroxydiphenoyl]-β-D-glucopyranoside (2), by time dependent density functional theory (TDDFT) at B3LYP/6–31 G** level has identified the roles of the (2S)-flavanone and (S)-HHDP moieties in generating its ECD spectrum and provided theoretical evidence for the empirical ECD rules applicable to flavanones and HHDP-containing compounds. The experimentally observed positive Cotton effect (CE) around 240 nm in 2 is derived from the (S)-HHDP chromophore, while the broad negative CE in the region of 260–300 nm is contributed by both the (S)-HHDP and (2S)-flavanone moieties. The ‘linker’ glucosyl moiety has little effect on the overall ECD. It appears that the respective chromophores in 2 contribute additively to the overall ECD and the empirical rules are applicable for configurational assignment. However, if an (R)-HHDP chromophore is present as shown in mattucinol-7-O-[4″,6″-O-(R)-hexahydroxydiphenoyl]-β-D-glucopyranoside (3), the dominant role of the (R)-HHDP and interaction between the (R)-HHDP and (2S)-flavanone moieties to its overall ECD may be confusing when applying the empirical rules to experimental ECD interpretation. Thus, theoretical calculation of the ECD that quantifies the contributions and interactions of different chromophores is essential for the assignment of the absolute configuration of this class of naturally occurring compounds.