ABSTRACT

The leaves of Mezoneuron benthamianum yieldedmethyl gallate and gallic acid as the constituentsresponsible for its antibacterial activity. (-)-Shikimicacid-3-O-gallate, 1-O-methyl-D-chiro-inositol, (-)-epi-catechin, (-)-epicatechin-3-gallate and kaempferol-3-(6''-galloyl) glucoside were also isolated. Theminimum inhibitory concentrations of these com-pounds against some Gram-positive and Gram-nega-tive microorganisms and a fungus are presented.

INTRODUCTION

Mezoneuron benthamianum Baill. (Leguminoseae) is ashrub or woody climber, up to 25 feet high. The stemsand rachis are covered with short recurved thorns. Adecoction of the root, bark and leaves is used in Guineafor urethral discharges (Burkill, 1985). An infusion ofthe dried root is drunk or used as a bath for generalmalaise in Senegal. The leaves of this plant showedantimicrobial activity (Binutu, 1998). No informationwas found in the literature on the chemical constituentsof this plant. Fractionation of the ethyl acetate andbutanol extracts of the leaves of this plant where theantimicrobial activity resided led to the isolation ofsome gallic acid derivatives. We report the isolation ofmethyl gallate (1), gallic acid (2), (-)-shikimic acid-3-

O-gallate (3), 1-O-methyl-D-chiro-inositol (4), (-)-epi-catechin (5), (-)-epicatechin-3-gallate (6) andkaempferol-3-(6''-galloyl)glucoside (7) from the leavesof Mezoneuron benthamianum and their effects againstsome Gram-positive and Gram-negative micro-organisms and a fungus.

MATERIALS AND METHODS

Experimental ProceduresAll melting points were measured on a Kofler hot plateand are uncorrected. 1H NMR and 13C NMR spectrawere run at 300 and 75 MHz, respectively (Bruker 300MHz spectrometer) in DMSO-d6, MeOD or CDCl3using tetramethylsilane (TMS) as internal standard andcoupling constants (J) are in Hz. Standard Brukersequences were used for APT, COSY, HMQC, HMBCand NOESY experiments. Column chromatography(CC) was carried out using silica gel or Sephadex LH20and thin-layer chromatography (TLC) on silica gel. UVspectra were recorded in MeOH or CHCl3.

Plant MaterialThe leaves of Mezoneuron benthamianum were col-lected in Ibadan, Nigeria in March, 1997. The plant wasidentified by Dr. Z. Gbile, and a herbarium specimen isdeposited at the Forestry Research Institute of Nigeria,Ibadan (FRIN No. 105345).

Extraction and IsolationThe air-dried powdered leaves of Mezoneuron ben-thamianum (1 kg) were percolated to exhaustion withMeOH at RT. The solution was evaporated in vacuo toyield a brown gummy residue (109 g). An aqueous sus-pension of this residue was extracted successively threetimes each with CHCl3 and BuOH. The respective

Keywords: Antibacterial activity, gallic acid derivatives,Mezoneuron benthamianum.

Address correspondence to: G.A. Cordell, Department ofMedicinal Chemistry and Pharmacognosy, College of Phar-macy, University of Illinois at Chicago, 833 S. Wood Street,Chicago, IL 60612, USA. Tel: 312-996-7245. Fax: 312-996-7107. E-mail: cordell@uic.edu

Pharmaceutical Biology 1388-0209/00/3804-0284$15.002000, Vol. 38, No. 4, pp. 284–286 © Swets & Zeitlinger

GALLIC ACID DERIVATIVES FROM MEZONEURON BENTHAMIANUM

LEAVES

Oluwatoyin A. Binutu and Geoffrey A. Cordell*

Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, University of Illinois atChicago, Chicago, IL 60612, USA

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extracts were combined and evaporated under reducedpressure to give CHCl3 (53 g) and BuOH (37 g) frac-tions. The BuOH extract (35 g) was cc on Si gel(70–230 mesh, Merck) eluting with CHCl3 followed bygradient mixtures of CHCl3-EtOAc, EtOAc-MeOH,and MeOH. Fractions were collected and pooledaccording to their similarity by TLC eluting withEtOAc-MeOH-H2O (9:1:1), to give four fractions (A1-A4). Further repeated purification of subfractions A1and A2 on Si gel afforded compounds 1 (320 mg) and2 (29 mg), respectively. Repeated fractionation of sub-fraction A3 (8.75 g) on Sephadex LH-20 eluting withH2O-MeOH (5:5) and on Si gel, furnished compounds3 (55 mg), 4 (3.72 g), 5 (2.58 g), 6 (35 mg), and 7 (92mg). Purification of A3 was monitored by TLC on RP-18 eluted with MeOH-H2O (1:1).

Biological ActivityMinimum inhibitory concentrations (MICs) of isolatedcompounds against two Gram-positive (Staphylo-coccus aureus ATCC 29213, Bacillus subtilis ATCC21394) two Gram-negative (Escherichia coli ATCC25922, Pseudomonas aeruginosa ATCC 27853) organ-isms and a fungus (Candida albicans ATCC 24433)were determined using the two-fold serial broth dilu-tion technique (Reeves et al., 1978). Ampicillin,erythromycin and clotrimazole were used as standardantibiotics for comparison.

RESULTS AND DISCUSSION

Compounds 1–7 were identified by spectral data (UV,MS, 1H NMR and 13C NMR) and comparison with lit-erature values as methyl gallate (1) (Hussain et al.,

1979), gallic acid (2) (Hussain et al., 1979), (-)-shikimic acid-3-O-gallate (3) (Nonaka et al., 1985), 1-O-methyl-D-chiro-inositol (4) (Wells & Bohm, 1980),(-)-epicatechin (5) (Nonaka et al., 1983), (-)-epicate-chin-3-O-gallate (6) (Nonaka et al., 1983) andkaempferol-3-(6''-galloyl)glucoside (7) (Markham etal., 1978, Aquino et al., 1988).

The minimum inhibitory concentration (MIC) of theisolated compounds (Table 1) showed that gallic acidand its methyl ester were weakly active against theGram-positive and Gram-negative microorganisms, butnot the fungus. The higher antibacterial activity of gal-lic acid methyl ester relative to gallic acid is consistentwith previous reports (Hussain et al., 1979, Boyd &Beveridge, 1981). Some of the other compounds wereactive against Gram-positive bacteria (S. aureus, Bacil-lus subtilis), but not the Gram-negative microorganisms(P. aeruginosa, E. coli) and the fungus (Candida albi-cans). The antimicrobial potential of the isolated com-pounds, though very weak, may account for the use ofthe plant in traditional medicine. Epicatechin andrelated compounds have been found to have antimuta-genic and anticarcinogenic (Gali et al., 1994), immuno-stimulant (Wagner et al., 1985), antiviral (Takechi et al.,1985), antiallergic (Kakegawa et al., 1985), and anti-hypertensive (Inokuchi et al., 1985) effects.

ACKNOWLEDGEMENTS

This work was supported, in part, by Grant F05 TW05372from the Fogarty International Center, National Institutes ofHealth, Bethesda, MD to O. A. B.

GALLIC ACID DERIVATIVES FROM MEZONEURON BENTHAMIANUM LEAVES 285

Table 1. Minimum inhibitory concentrations of gallic acid derivatives from Mezoneuron benthamianum leaves against microorganisms.

MIC �g/mlTested compounds Microorganisms

S. aur B. sub E. coli P. aeru C. albi

Gallic acid 250 250 1000 1000 NAMethyl gallate 125 125 250 500 NA(-)-Shikimic acid-3-O-gallate 1000 1000 NA NA NA(-)-Epicatechin 1000 1000 NA NA NA(-)-Epicatechin-3-O-gallate 1000 1000 NA NA NA1-O-Methyl-D-chiro-inositol NA NA NA NA NAKaempferol-3-(6''-galloyl)glucoside 1000 1000 NA NA NAAmpicillin 2 5 10 25 NTErythromycin 1 5 25 25 NTClotrimazole NT NT NT NT 25

S. aur – Staphylococcus aureus, B. sub – Bacillus subtilis, E. coli – Escherichia coli, P. aeru – Pseudomonas aeruginosa, C. albi – Candidaalbicans.NA – Not active, NT – Not tested.

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Accepted: January 3, 2000

286 O.A. BINUTU AND G.A. CORDELL

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