First report of antioxidative abeo-oleanenes from red seaweed Gracilaria salicornia as dual inhibitors of starch digestive enzymes

Carbolytic enzyme-associated cascades have been considered as potential curative target in attenuating diabetic mellitus pathogenesis. Two oleanene class of triterpenoids characterised as 24(4 -> 23), 27(8 -> 26), 30(20 -> 29)-tris-abeo-olean-(12-oxo)-1,15,22-triene-methyl hept-5-enoate (1) and 24(4 -> 23)-abeo-olean-(12-oxo)-3,5-diene-deconoate (2) with potential inhibitory activities against the starch digestive enzymes alpha-glucosidase and alpha-amylase, were purified from the organic extract of intertidal red seaweed Gracilaria salicornia (family Gracilariaceae). Structural interpretation of compounds was carried out by detailed spectroscopic analysis, and their antioxidant/anti-diabetic potentials were assessed. Inhibitory potential of abeo-oleanene derivative (2) towards the starch digestive enzymes, alpha-glucosidase (IC50 0.29 mM) and alpha-amylase (IC50 0.32 mM) were greater than those displayed by its abeo-oleanene chemotype 1 (IC50 0.34-0.40 mM). The molecular modelling studies were performed to designate the alpha-amylase and alpha-glucosidase inhibitory mechanism of oleanene analogues, and the comparison of docking parameters suggested that compound 2 exhibited least binding energy of -10.04 and -9.84 kcal mol(-1) towards alpha-amylase and alpha-glucosidase respectively, and those results were corroborated with its greater inhibition potential against carbolytic enzymes. These results demonstrated that abeo-oleanene derivative (2) might constitute prospective anti-hyperglycaemic pharmaceutical candidate to moderate the likelihood of type-II diabetes.