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.