Antioxidative dolabellanes and dolastanes from brown seaweed Padina tetrastromatica as dual inhibitors of starch digestive enzymes.

New dolabellanes {6-methoxy-dolabella-8(17),12-diene-10β,18-diol (1), 3-methoxy-dolabella-12(18)-ene-4β-ol (2), 3-methoxy-dolabella-10,18(19)-diene-5α,8β-diol (3)} and dolastanes {2,7-dimethoxy-14α-hydroxy-dolasta-1(15),9-diene (4) and 4,7-dimethoxy-9β,14α-dihydroxy-dolasta-1-ene (5)} were identified from brown seaweed Padina tetrastromatica (family Dictyotaceae), collected from the southeast coast of India. Compounds 1-3 were found to possess dolabellane skeleton with [9.3.0] cyclotetradecane framework whereas, 4-5 were composed of tricyclic diterpenes with linear arrangement of six-seven-five fused alicyclic rings. Compounds 3 and 5 registered greater antioxidative activities (IC50 ≤0.63 mg/mL) than other analogues (IC50 ≥0.65 mg/mL), whereas their attenuating potentials against carbolytics α-amylase and α-glucosidase (IC50 ∼0.12-0.14 mg/mL) were comparable with those displayed by acarbose (IC50 0.14-0.12 mg/mL). Bioactive potentials of titled compounds were assessed by electronic and lipophilic parameters. The lesser binding energies of 3 (-9.71 kcal/mol) and 5 (-8.59 kcal/mol) through molecular docking demonstrated their effective hydrogen bonding interactions with α-amylase. Thus, dolabellanes and dolastanes might be used as anti-diabetic and antioxidant leads to reduce the risk of hyperglycaemia.