Isolation and identification of two novel compounds from Marsdenia roylei and their quantum chemical calculations.

Two new compounds 1 (Methyl 26-di-deoxy-6-methyl-β-D-allohexopyranoside) and 3 (3, 11, 12, 20 tetra-O-acetyl-pregn-5-ene-14β-ol) have been isolated from the chloroform-soluble extract of the whole plant of Marsdenia roylei (family: Asclepiadaceae) and their structures were determined by 1D, 2D NMR and ESI-MS as well as by chemical modification. We have calculated the molecular geometries, local reactivity descriptors by the density functional theory with B3LYP functional with basis set 6-311G+(d,2p) of 1, 3 and 4 (deacylated 3). The H and C NMR chemical shifts of 1, 3 and 4 were calculated using Gauge-Including Atomic Orbital approach and these values are correlated with the experimental observations.