Ent–Clerodane Diterpenoid Inhibitors of Glucose-6-phosphatase from Croton guatemalensis Lotsy

The Croton genus includes a diverse group of plants with remarkable potential in natural products research, particularly due to their bioactive compounds with hypoglycemic and phytochemical significance. This study examines Croton guatemalensis Lotsy, focusing on its chemical composition and its biological efficacy as a glucose-6-phosphatase inhibitor. Phytochemical analysis led to the isolation and structural elucidation of eleven compounds (1–11), including three new ent−clerodane diterpenes, designated crotoguatenoic acids C (9), D (10), and E (11). The absolute configurations of compounds 9–11 were determined by electronic circular dichroism (ECD) as (5R,8R,9R,10S)-configured ent–clerodanes. High-performance liquid chromatography–mass spectrometry (HPLC–MS/MS) revealed 25 peaks tentatively assigned to terpenoids, flavonoids, and alkaloids, highlighting the species’ chemical diversity. In vitro assays using ethanol–water extract (EWE) and isolated compounds with rat liver microsomes demonstrated inhibitory activity against glucose-6-phosphatase (G6Pase), particularly among ent–clerodane diterpenes (73–96%), with EWE and compounds 1, 4, and 11 showing the highest inhibition. Molecular docking analysis revealed strong interactions between these diterpenoids and the G6PC1 binding pocket, with binding energies comparable to chlorogenic acid (positive control). These findings position C. guatemalensis as a valuable source of bioactive diterpenoids and support the potential of ent-clerodane derivatives as natural G6Pase inhibitors for hyperglycemia management.