Phytochemical Constituents, Antimicrobial Activity of Daniellia oliveri, and X-ray Crystal Structure of Polyalthic Acid

Abstract

Objectives: Daniellia oliveri Rolfe is a well-known plant of Fabaceae family whose previous phytochemical and pharmacological studies led to the identification of triterpenoid, phenol, anthraquinone oxalate with antioxidant, antibacterial and antifungal activities. This study aimed to investigate chemical constituents and evaluate the antimicrobial potency of the root of D. oliveri. Methods: The methanol extract of the root barks of D. oliveri was subjected to silica gel chromatographic separation. The structures of the isolated compounds (1-9) were determined by analyzing their spectrometric and spectroscopic spectra. Single-crystal-Xray analysis was used to establish the absolute skeletal structure of compound 1. Crude extract, fractions and compounds were investigated against four bacteria vis Pseudomonas aeruginosa 27853, Escherichia coli 5, Staphylococcus aureus 25923 and Streptococcus sp . 9619 and, two yeast vis Candida albicans14053 and Candida tropicalis 018 using broth microdilution method. Results: The phytochemical prospection of the methanol extract of D. oliveri allowed the isolation of a naturally crystallized diterpenoid type furolabdane: polyalthic acid 1, as well as eight amorphous compounds (2-9). Among the tested samples, the crude extract, fractions and compounds selectively showed inhibitory effects against the tested microorganisms with MIC values ranging from 4 to 1024 μg/mL. Fraction D1 and compounds 1, 4, 7, 8 and 9 exhibited the broadest antimicrobial effects among fractions and compounds while D5 and compound 1 showed the best activity with MIC values of 16 and 4 μg/mL respectively against E. coli which appeared to be the most sensitive strain . Conclusion: Polyaltic acid (1) showed the best activity with significant MIC value of 4 μg/mL identical to that of ceftazidine against E. coli. The MIC values of the active compounds 1, 4 and 7 are comparable to those of ceftazidime. Then, these compounds from natural origin, could serve as markers in the standardization of Daniellia plant as phytomedicine.