Triterpenoids and Semisynthetic Derivatives with Antimicrobial Activities from the Leaves of Caloncoba glauca (Flacourtiaceae)

Chemical investigation of the MeOH extract from the leaves of C. glauca yielded nine known triterpenoids (1-9) belonging to the cycloartane and friedelane series. Two of these compounds namely glaucartanoic acid A (1) and 3β,21β-dihydroxy-30-nor-(D:A)-friedoolean-20(29)-en-27-oic acid (5) were subjected to chemical derivatizations and afforded five new derivatives: diacetylglaucartanoic acid A (1a), 24-acetylglaucartanoic acid A (1b), glaucartanoic acid A methyl ester (1c), 24-methoxyglaucartanoic acid A methyl ester (1d), and 3β,21β-diacetoxy-30-nor-(D:A)-friedoolean-20(29)-en-27-oic acid (5a). Their structures were assigned based on their NMR and MS data and by comparison with literature values. The MeOH extract, isolated compounds and some new semi-synthetic derivatives were subjected to in vitro antimicrobial assays against a panel of pathogenic microorganisms, including Gram-positive and Gram-negative bacteria, and fungi using broth microdilution method. The MeOH extract displayed activity towards all the tested pathogenic bacterial and fungal strains with good activity (MIC against Staphylococcus aureus ATCC25923 and Shigella flexneri SDINT. Compounds 3 and 5 showed the most potent antimicrobial effect.