Stilbenoids from the bark of Hopea odorata: antioxidant and antidiabetic activities

Two previously undescribed tetrameric stilbenoids, named hopearatols A (1) and B (2), were isolated from the bark of Hopea odorata Roxb., along with 17 known stilbenoids. Their structures were elucidated by HRESIMS and NMR spectroscopic analyses, while the absolute configuration of hopearatol A (1) was determined by ECD calculations combined with DP4+ probability analysis. To our knowledge, hopearatol A (1) represents the first tetrameric stilbenoid featuring a cyclobutane-containing core embedded within a complex polycyclic framework. Both ethyl acetate and methanol extracts exhibited high total phenolic content (TPC), with values of 223.4 ± 2.8 and 264.0 ± 3.2 mg GAE/g, respectively. Selected compounds were evaluated for their antioxidant (DPPH) and α-glucosidase inhibitory activities. The newly isolated compounds 1 and 2 showed low DPPH radical scavenging activity but displayed considerable α-glucosidase inhibition relative to acarbose (IC₅₀ = 109.7 ± 0.8 and 174.0 ± 8.1 μM, respectively, vs. 913.7 ± 19.6 μM). Notably, 15 emerged as the most potent compound, demonstrating stronger radical scavenging capacity than ascorbic acid (IC₅₀ = 36.3 ± 1.3 μM vs. 86.5 ± 1.2 μM) and remarkable α-glucosidase inhibition (IC₅₀ = 27.9 ± 1.8 μM).