Antibacterial Activity of Ent-Clerodane-Type Diterpenoids and Flavonoids From the Roots of Croton pseudopulchellus Pax (Euphorbiaceae)

The phytochemical investigation of the root barks of Croton pseudopulchellus Pax yielded two new clerodane-type diterpenoids, crotopseudofurans A (1) and B (2) along with 14 known compounds (3-16). Compounds 2 and 3 were obtained as a mixture of C-12 epimers. Their structures were established by spectrometric and spectroscopic means, single-crystal x-ray diffraction analysis and by comparison with literature data. The single-crystal x-ray diffraction data of 5 is reported for the first time. Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of plant constituents were determined against Gram-positive and Gram-negative bacteria by using broth microdilution method. The methanol extract and fractions exhibited moderate broad-spectrum activity, with stronger effects against Gram-positive bacteria. Among the isolates, 7,8-dehydrocrotocorylifuran (6) and vitexin (9) emerged as the most promising candidates (MIC = 16-64 µg/mL) and demonstrated remarkable bactericidal activity against all the tested bacteria. Except compound 6, clerodane-type diterpenoids (1-5) showed weak or no activity. The findings support the ethnomedicinal relevance of Croton pseudopuchellus roots and warrant further mechanistic, toxicological and structure-activity relationship studies aimed at developing new antimicrobial agents.