Combretum woodii
Another member of the Combretaceae to receive closer attention was Combretum
woodii. Dried ground leaves of C. woodii were extracted with 10 different solvents
(hexane, diisopropyl ether, diethyl ether, methylene dichloride, ethyl acetate, tetra-
hydrofuran, acetone, ethanol, methanol, and water) to determine the best extrac-
tant for subsequent isolation and characterization of antibacterial compounds.
With the exception of the water extract, which had no antibacterial activity, the oth-
5.12 Results on Antibacterial Activity Obtained with Members of the Combretaceae 111
er extracts were bioactive with at least one of them exhibiting minimum inhibitory
concentration values of 0.04 mg mL–1 against Staphylococcus aureus, Pseudomonas
aeruginosa, Escherichia coli, or Enterococcus faecalis. Intermediate polarity solvents
extracted about 10% of the dry mass compared with about 3% with the more polar
or nonpolar solvents. These solvents also had higher antibacterial activity than
more polar or nonpolar extractants [59].
Ethyl acetate was the best extractant with an average MIC value of 0.08 mg mL–1
for the four pathogens, followed by acetone and methylene dichloride with values
of 0.14 mg mL–1. The average MIC values for the positive controls were 0.13 (am-
picillin) and 0.12 mg mL–1 (chloramphenicol). By taking the quantity extracted
from the leaf powder into consideration, the total activity was highest for methyl-
ene dichloride (1309 mL g–1) followed by acetone (1279 mL g–1) extracts. The anti-
bacterial activity was high enough to consider the use of extracts for clinical appli-
cation and to isolate and characterize antibacterial compounds from the extracts.
Based on the Rf values of the antibacterial compounds determined by bioautogra-
phy, the antibacterial compound was not a polyphenol or a tannin [59].
Acetone extracts of C. woodii leaf powder were separated by solvent–solvent par-
titioning into six fractions. The highest total activity was in the chloroform fraction.
This fraction contained mainly one compound active against S. aureus. This com-
pound was isolated by bioassay-guided fractionation using silica gel open column
chromatography and identified by NMR and MS as the stilbene 2′,3′,4-trihydroxyl,
3,5,4′-trimethoxybibenzyl (combretastatin B5) previously isolated from the seeds
of C. kraussii. It showed significant activity against S. aureus with an MIC of
16 μg mL–1 but with lower activity towards P. aeruginosa (125 μg mL–1), E. faecalis
(125 μg mL–1), and slight activity against E. coli. This is the first report of the anti-
microbial activity of combretastatin B5. Its concentration in the leaves was in the
order of 5–10 mg g–1 which makes the use of nonpolar leaf extracts a viable propo-
sition in treating some infections, particularly in resource-poor settings [60].
Another member of the Combretaceae to receive closer attention was Combretum
woodii. Dried ground leaves of C. woodii were extracted with 10 different solvents
(hexane, diisopropyl ether, diethyl ether, methylene dichloride, ethyl acetate, tetra-
hydrofuran, acetone, ethanol, methanol, and water) to determine the best extrac-
tant for subsequent isolation and characterization of antibacterial compounds.
With the exception of the water extract, which had no antibacterial activity, the oth-
5.12 Results on Antibacterial Activity Obtained with Members of the Combretaceae 111
er extracts were bioactive with at least one of them exhibiting minimum inhibitory
concentration values of 0.04 mg mL–1 against Staphylococcus aureus, Pseudomonas
aeruginosa, Escherichia coli, or Enterococcus faecalis. Intermediate polarity solvents
extracted about 10% of the dry mass compared with about 3% with the more polar
or nonpolar solvents. These solvents also had higher antibacterial activity than
more polar or nonpolar extractants [59].
Ethyl acetate was the best extractant with an average MIC value of 0.08 mg mL–1
for the four pathogens, followed by acetone and methylene dichloride with values
of 0.14 mg mL–1. The average MIC values for the positive controls were 0.13 (am-
picillin) and 0.12 mg mL–1 (chloramphenicol). By taking the quantity extracted
from the leaf powder into consideration, the total activity was highest for methyl-
ene dichloride (1309 mL g–1) followed by acetone (1279 mL g–1) extracts. The anti-
bacterial activity was high enough to consider the use of extracts for clinical appli-
cation and to isolate and characterize antibacterial compounds from the extracts.
Based on the Rf values of the antibacterial compounds determined by bioautogra-
phy, the antibacterial compound was not a polyphenol or a tannin [59].
Acetone extracts of C. woodii leaf powder were separated by solvent–solvent par-
titioning into six fractions. The highest total activity was in the chloroform fraction.
This fraction contained mainly one compound active against S. aureus. This com-
pound was isolated by bioassay-guided fractionation using silica gel open column
chromatography and identified by NMR and MS as the stilbene 2′,3′,4-trihydroxyl,
3,5,4′-trimethoxybibenzyl (combretastatin B5) previously isolated from the seeds
of C. kraussii. It showed significant activity against S. aureus with an MIC of
16 μg mL–1 but with lower activity towards P. aeruginosa (125 μg mL–1), E. faecalis
(125 μg mL–1), and slight activity against E. coli. This is the first report of the anti-
microbial activity of combretastatin B5. Its concentration in the leaves was in the
order of 5–10 mg g–1 which makes the use of nonpolar leaf extracts a viable propo-
sition in treating some infections, particularly in resource-poor settings [60].
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