Phytochemical and biological activity studies on the twigs of Baikiaea plurijuga and the tubers of Ipomoea bolusiana

Abstract

Phytochemical studies on the twigs of Baikiaea plurijuga afforded four compounds, (+) – catechin, taxifolin, eriodictyol and sucrose. The dissertation describes the methods of their isolation and discusses their characterization. All the isolated compounds are being reported for the first time from this plant species. The isolated compounds and extracts from this plant were screened for their antioxidant activity using DPPH radical. Eriodictyol showed the highest radical scavenging activity among the tested flavonoid derivatives with an IC50 value of 0.047 ± 0.007 μM. The IC50 value was better than that of the standard ascorbic acid (0.090 ± 0.01 μM). The total phenolic content of the extracts was determined using the Folin-Ciocalteau method and the ethyl acetate extract exhibited the highest amongst the twigs of Baikiaea plurijuga extracts (350 mg GAE/g). Antimicrobial studies on both the extracts and pure isolates was done using the agar-overlay method and (+) – catechin exhibited the best inhibitory activity against gram-positive bacteria S. aureus at an MIQ of 5 μg. Eriodictyol on the other hand showed the best inhibition against gram-negative bacteria E. coli and P. aeruginosa at MIQs of 50 μg. Taxifolin exhibited the best activity against the test fungus C. albicans at an MIQ of 5 μg. Phytochemical studies on the tubers of Ipomoea bolusiana afforded seven compounds, (E)-octadec-11-en-1-yl (E)-3-(4-hydroxyphenyl) acrylate, (E)-icos-13-en-1-yl (E)-3-(3,4-dihydroxyphenyl) acrylate, methyl (E)-octadec-11-enoate, sucrose, maltose, C4C and IBMF2, all of which are reported for the first time from this plant species. Trans esterification of C4C afforded caffeic acid methyl ester. The extracts and isolated compounds from these tubers were screened for antimicrobial as well as antioxidant activities. Amongst the cinnamic acid derivatives isolated, (E)-icos-13-en-1-yl (E)-3-(3,4-dihydroxyphenyl) acrylate showed better radical scavenging activity with an IC50 value of 0.023 ± 0.006 μM as compared to (E)-octadec-11-en-1-yl (E)-3-(4-hydroxyphenyl) acrylate which showed an IC50 value of 0.47 ± 0.06 μM. Antimicrobial studies of the isolated compounds as well as the extracts revealed that C4C exhibited the best activity against gram-negative bacteria P. aeruginosa with an MIQ of 10 μg, while (E)-icos-13-en-1-yl (E)-3-(3,4-dihydroxyphenyl) acrylate exhibited weak activity against gram-positive bacteria S. aureus with an MIQ of 50 μg. Extracts of the tubers of this plants exhibited moderate activity against all the test microorganism at an average MIQ of 50 μg. The total phenolic content of the extracts revealed that the aqueous methanol (80 %) extract showed the highest among the extracts at 150 mg GAE/g.