Dynamic stereochemistry of erigeroside by measurement of 1H–1H and 13C–1H coupling constants

Erigeroside was extracted from Satureja khuzistanica Jamzad (Marzeh Khuzistani in Persian, family of lamiaceae), and 1H, 13C, 13C{1H}, 1H–1H COSY, HMQC and J-HMBC were obtained to identify this compound and determine a complete set of J-coupling constants (1JC–H, 2JC–H, 3JC–H and 3JH–H) values within the exocyclic hydroxymethyl group (CH2OH) and anomeric center. In parallel, density functional theory (DFT) using B3LYP functional and split-valance 6-311++G** basis set has been used to optimized the structures and conformers of erigeroside. In all calculations solvent effects were considered using a polarized continuum (overlapping spheres) model (PCM). The dependencies of 1J, 2J and 3J involving 1H and 13C on the C5′–C6′ (ω), C6′–O6′ (θ) and C1′–O1′ (φ) torsion angles in erigeroside were computed using DFT method. Complete hyper surfaces for 1JC1′,H1′, 2JC5′,H6′R, 2JC5′,H6′S, 2JC6′,H5′, 3JC4′,H6′R, 3JC4′,H6′S and 2JH6′R–H5′S as well as 3JH5′,H6′R were obtained and used to derive Karplus equations to correlate these couplings to ω, θ and φ. These calculated J-couplings are in agreement with experimental values. These results confirm the reliability of DFT calculated coupling constants in aqueous solution.