Bioactivity analysis of pentacyclic triterpenoids isolated from Metrosideros polymorpha

•Eleven pentacyclic triterpenoids including a novel compound were isolated from Metrosideros polymorpha.•Five compounds showed strongly GDH inhibitory activities.•Arjunolic acid displayed antifungal activity against Rhizoctonia solani and Magnaporthe oryzae.•Arjunolic acid displayed insecticidal activity against whitefly. Eleven compounds were isolated and identified from M. polymorpha, included one previously undescribed compound (1) and ten known compounds (2–11). Through NMR, HRESI-MS and ECD spectrum analysis, the planar and absolute structures of compound 1 were determined and identified as pentacyclic triterpenoid derivative. Among the rest 10 known compounds, 2–8 also were identified as pentacyclic triterpenoids. The antifungal, insecticidal activity and Glutamate dehydrogenase (GDH) inhibitory activity of the 11 compounds isolated from M. polymorpha were evaluated, and arjunolic acid (7) showed significant antifungal activity against hizoctonia solani and Magnaporthe oryzae with IC50 values 44.20 and 38.58 µg mL−1, respectively. Moreover, compound 7 displayed insecticidal activity against whitefly at a 100 µg mL−1 concentration with corrected mortality of 35.4%. In addition, compounds 2, 3, 4, 7 and 8 exhibited strong GDH inhibitory effects at both 20 and 50 µM, and compound 4 showed the most effective activity. The underlying inhibitory mechanism of compound 4 against GDH was confirmed as competitive inhibitors through molecular docking and enzyme kinetics. These results may lead to a potential application on agricultural and clinical use. [Display omitted]