Antimicrobial and antioxidant flavonoids from the leaves of Oncoba spinosa Forssk. (Salicaceae).
BACKGROUND
Naturally occurring flavonoids have been reported to possess various pharmacological properties. The aim of this study was to evaluate the antimicrobial and antioxidant activities of the MeOH extract and flavonoids from the leaves of Oncoba spinosa, a plant used for the treatment of syphilis, wounds and sexual impotence.


METHODS
The plant extract was prepared by maceration in methanol and sequentially fractionated by column chromatography. The structures of isolated compounds were elucidated on the basis of spectral studies and comparison with published data. The MeOH extract and its isolated compounds were evaluated for their antibacterial and antifungal activities by broth microdilution method. The 1,1-diphenyl-2-picrylhydrazyl (DPPH) and trolox equivalent antioxidant capacity (TEAC) assays were used to detect the antioxidant activity. The samples were tested spectrophotometrically for their hemolytic properties against human red blood cells.


RESULTS
The fractionation of the MeOH extract afforded five known flavonoids including kaempferol (1), quercetin (2), apigenin-7-O-β-D-glucuronopyranoside (3), quercetin 3-O-β-D-galactopyranoside (4) and quercetin 3-O-α-L-rhamnopyranosyl (1 → 6) β-D-glucopyranoside (5). The MeOH extract displayed weak to moderate antimicrobial activities (MIC = 256-2048 μg/ml). Quercetin 3-O-α-L-rhamnopyranosyl (1 → 6) β-D-glucopyranoside (5) and quercetin (2) were respectively the most active compounds against bacteria (MIC = 8-64 μg/ml) and fungi (MIC = 64 - 128 μg/ml). These tested samples also showed high radical-scavenging activities (EC50 = 5.08 - 70.56 μg/ml) and gallic acid equivalent antioxidant capacities (TEAC = 53.76 - 89.86 μg/ml) when compared with vitamin C (EC50 = 4.72 μg/ml). The MeOH extract and compounds 2-5 were non-toxic to human red blood cells indicating their high selectivity to be used as antimicrobial and antioxidant drugs.


CONCLUSIONS
The MeOH extract of O. spinosa as well as compounds 2 - 5 could be a potential source of natural antimicrobial and antioxidant products.
Chemistry Department, University of Dschang, PO Box 67, Dschang, Cameroon. djouossim@yahoo.com.
Marie Geneviève
MG
Djouossi
Laboratory of Microbiology and Antimicrobial Substances, Biochemistry Department, Faculty of Science, University of Dschang, PO Box 67, Dschang, Cameroon. jtamokou@yahoo.fr.
Jean-de-Dieu
JD
Tamokou
Chemistry Department, University of Dschang, PO Box 67, Dschang, Cameroon. dngnokam@yahoo.fr.
David
D
Ngnokam
Laboratory of Microbiology and Antimicrobial Substances, Biochemistry Department, Faculty of Science, University of Dschang, PO Box 67, Dschang, Cameroon. jrkuiate@yahoo.com.
Jules-Roger
JR
Kuiate
Chemistry Department, University of Dschang, PO Box 67, Dschang, Cameroon. tapondjou2001@yahoo.fr.
Leon Azefack
LA
Tapondjou
Service Commun d'Analyse, Institut de Chimie Moléculaire de Reims (ICMR), CNRS UMR 7312, Bat. 18 BP 1039, 51687, Reims cedex 2, France. dominique.harakat@univ-reims.fr.
Dominique
D
Harakat
Groupe Isolement et Structure, Institut de Chimie Moléculaire de Reims (ICMR), CNRS UMR 7312, Bat. 18 BP 1039, 51687, Reims cedex 2, France. laurence.voutquenne@univ-reims.fr.
Laurence
L
Voutquenne-Nazabadioko
D000890:Anti-Infective Agents / Q000302:isolation & purification / Q000494:pharmacology*; D000975:Antioxidants / Q000302:isolation & purification / Q000494:pharmacology*; D047310:Apigenin / Q000302:isolation & purification / Q000494:pharmacology; D001419:Bacteria / Q000187:drug effects*; D001713:Biphenyl Compounds / Q000378:metabolism; D005419:Flavonoids / Q000302:isolation & purification / Q000494:pharmacology*; D005658:Fungi / Q000187:drug effects*; D006801:Humans; D044949:Kaempferols / Q000302:isolation & purification / Q000494:pharmacology; D008297:Male; D010851:Picrates / Q000378:metabolism; D010936:Plant Extracts / Q000737:chemistry / Q000494:pharmacology*; D018515:Plant Leaves / Q000737:chemistry; D011794:Quercetin / Q000302:isolation & purification / Q000494:pharmacology; D031308:Salicaceae / Q000737:chemistry*
D000890:Anti-Infective Agents; D000975:Antioxidants; D001713:Biphenyl Compounds; D005419:Flavonoids; D044949:Kaempferols; D010851:Picrates; D010936:Plant Extracts; C006552:kaempferol; D047310:Apigenin; D011794:Quercetin; C004931:1,1-diphenyl-2-picrylhydrazyl