New terpenoids, stilbenoids and other metabolites from algae and coastal plants of Tanzania

The investigations reported in this thesis were aimed at establishing chemical constituents and biological activities of extracts from selected algal, mangrove and other plant species growing on shore and coastal Tanzania. Crude extracts of twenty three investigated species subjected to antiplasmodial, antimicrobial, antioxidant and cytotoxic assays exhibited activities with varying potencies with IC50 ranging from 0.45 to 75.7 µg/mL (againstPlasmodium falciparum (3D7 strain), MIC 0.3to 5.0 µg/mL (against Staphylococcus aureus, Streptococcus pyogenes, Pseudomonas aeruginosa,Escherichia coli, Candida albicans and Cryptococcus neoformans), EC50 1.0to 100 µg/mL (DPPH radical scavenging), LC50 0.75to 1000 µg/mL (cytotoxicity on brine shrimp larvae) and IC50 4.02 to 289 µg/mL (cytotoxicity against HEK 293 cells).Fifteen compounds were isolated by chromatographic separations of the methanolic extracts ofthe selected algal and coastal plant species and their structures were elucidated using spectrometric methods. Debromolaurinterol (3.1)and fucosterol (3.2) were isolated from the two algal species (Cystoseiramyrica and Padinaboryana, respectively). 3,3ʹ,4-Tri-O-methyl ether ellagic acid (4.1), lupeol (4.2), betulinic acid (4.3), stigmasterol (4.4) and tetramethyl ether scutellarein (4.5) were isolated from Sonneratia alba. Stuhlmannia moavi yielded four new compounds, stuhlmoavic acid (5.1), stuhlmoavinin (5.2), moavistilbenoxide (5.3a) [in a mixture with a known stilbenoid 3ʹ-hydroxypterostilbene (5.3)] and stuhlmanial (5.6) together with other four known compounds, 3ʹ-hydroxypterostilbene (5.3), cordylane C (5.4), tomocinol B (5.5) and amentoflavone (5.7). Structures of the isolated compounds were determined through analysis of their spectroscopic and spectrometric data. Compound 3.1 exhibited antiplasmodial activity with IC50 value of 20 µM while compound 3.2 showed weak activity at 40 µM. Compounds 4.1-4.4 and 5.1-5.7 were inactive at 30 ug/mL screening concentration against E. coli, Bacillus subtilis and S. epidermis. Bioactivities portrayed by the investigated extracts indicate their ingredients as potential sources of bioactive agents that warrant further explorations.