Anti-inflammatory and hypoglycaemic pentacyclic triterpenoids isolated from Lagerstroemia speciosa (L.) Pers. leaves.

The giant crepe-myrtle (Lagerstroemia speciosa (L.) Pers.) has a long history of medicinal use in Southeast Asia, and is widely cultivated as an ornamental plant. Its leaves are commonly brewed into tea, valued for their potential in preventing and treating diabetes and other ailments. Herein, a bioactive phytochemical investigation of the leaves led to the isolation and purification of 31 pentacyclic triterpenoids, including seven undescribed oleanane-type (1-3, 6-9), five undescribed ursane-type (10-14), two undescribed lupane-type (15-16) and 17 known pentacyclic triterpenes. The chemical structures of these compounds were elucidated using various spectroscopic techniques, including HR-ESI-MS, 1D and 2D NMR. The triterpenoids were assessed for their anti-diabetic and anti-inflammatory activities. Compounds 7 and 20 remarkably inhibited nitric oxide production in lipopolysaccharide-stimulated RAW 264.7 macrophages, with IC50 values of 34.12 ± 2.33 μM and 32.31 ± 4.73 μM, respectively. Furthermore, compounds 1, 10, 24, 28 and 30 demonstrated strong inhibitory effects on α-glucosidase. These findings suggest that L. speciosa leaves may offer promising potential in preventing diabetes and inflammation-related diseases.