Crystal structure and DFT calculations of andrographiside

Crystal and molecular structure of a labdane diterpenoid glucoside, andrographiside (1) is determined from 2D-NMR and X-ray diffraction data. The 2D-NMR study indicates that the carbohydrate moiety is in β-linkage and the sugar moiety is linked to C-19 of the aglycon. These observations are further confirmed from the X-ray diffraction studies. Both the six-membered rings are in chair conformation whereas the glucose ring adopts a twist-boat conformation. The molecular geometries and electronic structure of (1) were calculated at the DFT level using the hybrid exchange–correlation functional, BLYP, PW91 and PBE.