A new antibacterial tirucallane from Walsura trichostemon roots

The Genus Walsura: A Rich Resource of Bioactive Limonoids, Triterpenoids, and Other Types of Compounds

Medicinal plants of the genus Walsura (family Meliaceae) are native to tropical zones of a number of Asian countries, and have been used in systems of folk medicine. Several original research articles on Walsura species are available, but an overview highlighting the phytochemical and biological aspects of the compounds isolated to date is so far absent. Since the 1970s, phytochemical investigations on the genus Walsura have been undertaken, and more than 220 compounds from ten species have been identified. Natural products from Walsura species that have received the most attention are limonoids (114 compounds) and triterpenoids (72 compounds). Walsura limonoids have been characterized structurally as having diverse skeletons and more than 100 such compounds are new to the literature, while dammaranes, tirucallanes, and apotirucallanes are the main triterpenoid types from this genus. Other Walsura constituents comprise sesquiterpenoids, flavonoids, sterols, lignans, xanthones, and anthraquinones. Walsura species constituents have also been studied in natural product drug discovery screening programs. Many in vitro biological and some in vivo pharmacological investigations have been carried out on Walsura species isolated compounds. Walsura components display properties such as cancer cell cytotoxicity, antimicrobial, antidiabetes, anti-inflammatory, antioxidant, antifeedant, antifertility, ichthyotoxic, and neuroprotection activities.

A New Apotirucallane from Walsura trichostemon Leaves and Its Antibacterial and α-Glucosidase Inhibitory Activities

Phytochemical investigation of Walsura trichostemon leaves led to the isolation of a new apotirucallane-type triterpenoid, 11,25-dideacetyl-16-hydroxytrichostemonate (1), along with two known apotirucallane-type triterpenoids (2 and 3), two known tirucallane-type triterpenes (4 and 5), and two known steroids (6 and 7). Their structures were identified by intensive analysis of 1D and 2D nuclear magnetic resonance, infrared, and mass spectrometry data, which were compared with data reported in the literature. Compounds 2, 3, and 5 exhibited moderate antibacterial activity against Pseudomonas aeruginosa (minimum inhibitory concentration (MIC) value: 64 μg/mL), and compound 4 showed weak antibacterial activity against P. aeruginosa (MIC: 128 μg/mL). Furthermore, compound 5 displayed activity against Bacillus cereus (MIC: 64 μg/mL). In addition, compound 4 showed stronger α-glucosidase inhibitory activity than the control, acarbose. The active compound 4 was subjected to molecular docking experiments using AutoDock4 and revealed precise interactions with the active gorge of the enzyme through hydrogen bonding, supporting the in vitro results.