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Molecules 2013, 18(10), 12633-12644; doi:10.3390/molecules181012633
Article

Antimicrobial and Selected In Vitro Enzyme Inhibitory Effects of Leaf Extracts, Flavonols and Indole Alkaloids Isolated from Croton menyharthii

1,2
,
1
,
1
 and
1,*
1 Research Centre for Plant Growth and Development, School of Life Sciences, University of KwaZulu-Natal Pietermaritzburg, Private Bag X01, Scottsville 3209, South Africa 2 Department of Chemistry, Obafemi Awolowo University, Ile-Ife 220005, Nigeria
* Author to whom correspondence should be addressed.
Received: 12 July 2013 / Revised: 9 September 2013 / Accepted: 17 September 2013 / Published: 11 October 2013
(This article belongs to the Special Issue Structure-Activity Relationship of Flavonoids)
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Abstract

Croton species are used in folk medicine in the management of infections, inflammation and oxidative stress-related diseases. In order to isolate, characterize and evaluate the bioactive constituents of Croton menyharthii Pax leaf extracts, repeated column fractionation of the ethyl acetate fraction from a 20% aqueous methanol crude extract afforded three flavonols identified by NMR (1D and 2D) spectroscopic methods as myricetrin-3-O-rhamnoside (myricetrin, 1), quercetin-3-O-rhamnoside (2) and quercetin (3) along with an indole alkaloid, (E)-N-(4-hydroxycinnamoyl)-5-hydroxytryptamine, [trans-N-(p-coumaroyl) serotonin, 4]. All the compounds are reported from the leaf extract of this plant for the first time. The crude extracts, four solvent fractions (hexane, DCM, ethyl acetate and butanol) and isolated compounds obtained from the leaves were evaluated for their inhibitory effects on selected bacteria, a fungus (Candida albicans), cyclooxygenase (COX-2), α-glucosidase and acetylcholinesterase (AChE). Amongst the compounds, quercetin (3) was the most active against Bacillus subtilis and Candida albicans while myricetrin-3-O-rhamnoside (1) and trans-N-(p-coumaroyl) serotonin (4) were the most active compounds against Escherichia coli, Klebsiella pneumonia and Staphylococcus aureus. The inhibitory activity of myricetrin-3-O-rhamnoside (1) against COX-2 was insignificant while that of the other three compounds 24 was low. The AChE inhibitory activity of the alkaloid, trans-N-(p-coumaroyl) serotonin was high, with a percentage inhibitory activity of 72.6% and an IC50 value of 15.0 µg/mL. The rest of the compounds only had moderate activity. Croton menyharthii leaf extracts and isolated compounds inhibit α-glucosidase at very low IC50 values compared to the synthetic drug acarbose. Structure activity relationship of the isolated flavonols 13 is briefly outlined. Compounds 14 and the leaf extracts exhibited a broad spectrum of activities. This validates the ethnomedicinal use of the plant in folk medicine.
Keywords: Croton menyharthii Pax; flavonols; alkaloid; COX-2; antimicrobial; alpha-glucosidase; mutagenicity Croton menyharthii Pax; flavonols; alkaloid; COX-2; antimicrobial; alpha-glucosidase; mutagenicity
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Aderogba, M.A.; Ndhlala, A.R.; Rengasamy, K.R.R.; Van Staden, J. Antimicrobial and Selected In Vitro Enzyme Inhibitory Effects of Leaf Extracts, Flavonols and Indole Alkaloids Isolated from Croton menyharthii. Molecules 2013, 18, 12633-12644.

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