university of kwazulu-natal faculty of science and agriculture school ...
university of kwazulu-natal faculty of science and agriculture school ...
university of kwazulu-natal faculty of science and agriculture school ...
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2.5 Biological activity <strong>of</strong> the phytochemical constituents <strong>of</strong> Plectranthus<br />
The antibacterial <strong>and</strong> antifungal activities <strong>of</strong> abietanes isolated from Plectranthus species<br />
are listed in table 11. Of the one-hundred <strong>and</strong> fifty abietanes isolated from Plectranthus<br />
<strong>and</strong> Coleus species, only twenty are reported as having showed antimicrobial activity.<br />
These twenty abietanes were isolated from eight Plectranthus species with horminone<br />
(28), 7α-acetoxy-6β-hydroxyroyleanone (36), 7α,12-dihydroxy-17(15→16)-abeoabieta-<br />
8,12,16-triene-11,14-dione (55), 16-acetoxy-7α,12-dihydroxy-8,12-abietadiene-11,14-<br />
dione (54) <strong>and</strong> Coleon U (149) being isolated from more than one species.<br />
Of all the abietanes isolated from Plectranthus <strong>and</strong> Coleus species the highest<br />
antibacterial <strong>and</strong> antifungal activities were shown by the royleanone <strong>and</strong> coleon type<br />
compounds. These were compounds 28, 36, 38 (7α-formyloxy-6β-hydroxyroyleanone),<br />
44 (coleon U quinone) <strong>and</strong> 149. All these compounds are structurally related <strong>and</strong> have<br />
the same basic skeleton with different functional groups located in the molecules.<br />
However, coleon U has an aromatic ring <strong>and</strong> the others have a hydroxyquinoid ring C.<br />
Bacillus subtilis <strong>and</strong> Staphylococcus aureus were the most commonly tested bacterial<br />
strains while the anti-fungal pathogens tested were Cladosporium cucumerinum,<br />
Rhizoctonia solani, Sclerotinia sclerotiorum, Pythium ultimum <strong>and</strong> C<strong>and</strong>ida albicans.<br />
Acetone was the most frequently used solvent for extraction, while dichloromethane,<br />
chlor<strong>of</strong>orm <strong>and</strong> ethyl acetate were reportedly used only once for the extraction <strong>of</strong><br />
abietanes from the plant material.<br />
Of the eight antimicrobial studies carried out on abietanes, two were done on the roots<br />
only <strong>and</strong> two on the entire plant. The rest <strong>of</strong> the studies were carried out on the aerial<br />
parts <strong>of</strong> the plant <strong>and</strong> the leaves (aerial parts in many instances mean leaves <strong>and</strong> flowers).<br />
Comparative studies need to be done on the different plant parts, to ascertain where the<br />
largest concentration <strong>of</strong> abietane diterpenoids exist.<br />
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