Medicinal plants are known as sources of potential antimicrobial compounds belonging to different classes. The aim of the present work was to evaluate the antimicrobial potential of the crude extract, fractions, and some isolated secondary metabolites from the leaves of Macaranga occidentalis, a Cameroonian medicinal plant traditionally used for the treatment of microbial infections. Repeated column chromatography of the ethyl acetate and n-butanol fractions led to the isolation of seventeen previously known compounds (1−17), among which three steroids (1−3), one triterpene (4), four flavonoids (5−8), two stilbenoids (9 and 10) four ellagic acid derivatives (11−14), one geraniinic acid derivative (15), one coumarine (16), and one glyceride (17). Their structures were elucidated mainly by means of extensive spectroscopic and spectrometric (1D and 2D NMR and, MS) analysis and comparison with the published data. The crude extract, fractions, and isolated compounds were all screened for their antimicrobial activity. None of the natural compounds was active against Candida strains. However, the crude extract, fractions, and compounds showed varying levels of antibacterial properties against at least one of the tested bacterial strains, with minimal inhibitory concentrations (MICs) ranging from 250 to 1000 μg/mL. The n-butanol (n-BuOH) fraction was the most active against Escherichia coli ATCC 25922, with an MIC value of 250 μg/mL. Among the isolated compounds, schweinfurthin B (10) exhibited the best activity against Staphylococcus aureus NR 46003 with a MIC value of 62.5 μg/mL. In addition, schweinfurthin O (9) and isomacarangin (6) also exhibited moderate activity against the same strain with a MIC value of 125 μg/mL. Therefore, pharmacomodulation was performed on compound 6 and three new semisynthetic derivatives (6a–c) were prepared by allylation and acetylation reactions and screened for their in vitro antimicrobial activity. None of the semisynthetic derivatives showed antimicrobial activity against the same tested strains. The chemophenetic significance of the isolated compounds is also discussed in this paper.

Background: The germs of waterborne diseases are often associated with an increase in resistance, which contrasts with the discovery of new active molecules, thus complicating treatment. Research is therefore undertaken to discover new substances with therapeutic potential. Although plants are an important source for obtaining interesting compounds, methods based on synthetic chemistry make it possible to obtain compounds inspired by those found in nature and presenting equally important properties. One group of these compounds, called chalcone, is of great importance nowadays due to the diversity of biological activities it presents; therefore, many chalcone derivatives are synthesized and their biological activities evaluated. Methodology: The compounds were synthesized by Claisen-Schmidt condensation in a basic medium (potash 5%). The reaction was followed by thin layer chromatography. At the end of the reaction, filtration after cooling of the reaction medium allowed the collection of part of the product that precipitated, while liquid-liquid extraction (water-acetate) allowed to obtain the rest still dissolved. The products obtained were purified by column chromatography using the Hexane/Ethyl Acetate system. The characterization of the products was carried out on the physical properties and also the nuclear magnetic resonances of the proton and carbon 13. The use of isolation media for each of the 04 bacteria studied, namely ENDO, SS, TCBS and BEA agars, permitted the isolation of Escherichia coli, Salmonella typhi, Vibrio cholerae and Streptococcus feacalis, respectively. The microbiological technique for counting bacterial colonies in solid medium, as well as the microdilution in liquid medium allowed the evaluation of the action of the different chalcones. Results: Four O-propargyl vanillinic chalcones 5a-5d were obtained by Claisen Schmidt condensation method with respective yields of 63.6%; 66.7%; 66.7% and 70.0%. The evaluation of their antibacterial activities was done on four strains of bacteria including E. coli, S. typhi, V. cholerae and S. feacalis isolated from wells in the city of Yaoundé. Statistical data from the results of the solid-state bacterial colony counting technique revealed a lack of significance (p > 0.05) with respect to the variation of the mean bacterial abundance as a function of the concentrations of each chalcone (except that of the S. feacalis with respect to compound 5b). The results of the microdilution test showed the lowest MIC values with compound 5d (250 µg/mL), against S. typhi. Chalcones 5c and 5d exhibited better activity on E. coli (MIC value of 500 µg/mL) compared to the reference antibiotic: ampicillin (MIC > 1000 µg/mL).  Chalcones 5a and 5b were the least active on all bacteria studied, with MIC values greater than or equal to 1000. Conclusions: The microdilution tests showed an antibacterial activity of the synthesized compounds, with a better activity for the chalcone 5d.