Chemical Constituents from the Stem Bark of Ficus thonningii and their Chemotaxonomic Significance

Background of the Study: Tropical plants of the Ficus genus (Moraceae) are among the earliest fruit trees that humans have cultivated. Since ancient times, many folk medicines have used species of this genus to treat a variety of ailments. Evidence from earlier investigations has shown these plants contain abundant secondary metabolites with a variety of structural properties and biological functions. Place and Duration of Study: The research was carried out at the University of Nairobi (Faculty of Science and Technology, Department of Chemistry) from January to June 2022. Aim: The study focuses on isolating and identifying secondary metabolites from the stem bark of Ficus thonningii Blume found in Kenya and their chemotaxonomic significance. Methodology: Dried powdered stem bark of Ficus thonningii was extracted by maceration at room temperature using CH2Cl2/CH3OH (1:1) to yield a crude extract which was fractionated in a chromatographic column (CC) using silica gel (60 – 120 mesh) as an adsorbent eluting with EtOAc/n-hexane followed by CH3OH/EtOAc. The fractions were purified using silica gel (70 – 230, 230 – 400 mesh) CC and chromatotron eluting with solvents of different polarity, as well as a crystallization technique. Structures of the isolated compounds were elucidated and identified using the spectroscopic method (NMR (1D and 2D)) and by comparison with reported literature data. Results: Phytochemical investigation of the stem bark of Ficus thonningii afforded seven compounds, including yukovanol (1), 5,7,4′-trihydroxy-3′-(2-hydroxy-3-methyl-3-butenyl)isoflavone (2), cajanin (3), taxifolin (4), protocatechuic acid (5), saccharose (6), and stigmasterol (7). Compounds 1 - 3, 5 and 7 were not reported from F. thonningii until now. Further, compound 6 is being isolated from the genus Ficus for the first time. Conclusion: The chemotaxonomic significance of the isolated phytochemicals demonstrates the taxonomic position of F. thonningii in the genus Ficus and explains its multiple ethnomedicinal applications.