Phytochemical investigation of surface exudates of dodonaea angustifolia and senecio roseiflorus for bioactive principles

Abstract

The phytochemistry of the surface exudates of Dodonaea angustifolia (from two locations Ngong forest and Voi) and Senecio roseiflorus, as well as the antiplasmodial activity against chloroquine-sensitive (D6) and chloroquine-resistant (W2) strain of Plasmodium falciparum, for some of the isolated compounds, larvicidal activity against Aedes aegypti larvae, anti­ microbial activity against three strains of bacteria: Staphyloccocus aureus (A TCC2973 7), Escherichia coli (A TCC25922) and Bacillus pumilus (local strain) and a local strain of fungus, Saccharamyces cerevisiae and radical scavenging activity towards 1, I-diphenyl-2- picrylhydrazyl (DPPH) were carried out. The structures of the isolated compounds were determined using a combination of spectroscopic techniques [NMR, MS and UV].

The surface exudates of the fresh leaves of D. angustifolia growing in Ngong were extracted by successive dipping into fresh portions of acetone for short periods (15 seconds). The surface exudates showed anti-plasmodial activity with rcso values of 41.5 ± 3.9 ug/ml against chloroquine-sensitive (06) strain of the P. Jalciparum. The larvicidal activity of this extract

was not good, as its LCso value against the larvae of Aedes aegypti was> 60 ug/ml after 24 hours. The radical scavenging activity (RSA) of the extract towards OPPH was 54.6% at 11.4 ug/ml. The surface exudates showed activity against Staphyloccocus aureus (ATCC29737), Escherichia coli (ATCC25922) bacteria and Saccharamyces cerevisiae fungus.

The extract was subjected to a combination of chromatographic techniques leading to isolation of the fiavonoids, 5-hydroxy-3,7,4'-trimethoxyfiavone (1), 3,5-dihydroxy-7,4',­ dimethoxyfiavone (2), kumatakenin (3), santin (4), rhamnocitrin (5), isokaempferide (6), 6- methoxykaempferol (7), and pinocembrin (8); and the diterpenoids, 2[3-hydroxyhardwickic acid (9), dodonic acid (10) and ent-3[3,8a; 15,16-epoxy-13(16), 14-labdadiene-3,8-diol (11). All the compounds except santin (4) are reported from D. angustifolia for the first time from this plant. The fiavonoids, 5-hydroxy-3,7,4'-trimethoxyfiavone (1), 3,5-dihydroxy-7,4',­ dimethoxyfiavone (2), kumatakenin (3), rhamnocitrin (5) were also isolated from the two collections of D. angustifolia (Taita hill near Voi town). However, the rest of the compounds were present only from the D. angustifolia (Ngong'forest) refiecting geographical variability

in this species.

Most of the isolated compounds showed moderate anti-plasmodial activity against the 06 strain of Plasmodium Jalciparum with ICso values between 7.6 ± 2.3 for kumatakenin and 18.4 ± 4.8 for o-methoxykacmpferol. Among the compounds tested for larvicidal activity