Elsevier

Phytochemistry

Volume 107, November 2014, Pages 148-154
Phytochemistry

Galloylated flavonol rhamnosides from the leaves of Calliandra tergemina with antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA)

https://doi.org/10.1016/j.phytochem.2014.07.028Get rights and content

Highlights

  • Galloylated flavonol rhamnosides were isolated from leaves of Calliandra tergemina.

  • Acylation of flavonol rhamnosides was important for anti-MRSA activity.

  • Isolated flavonol rhamnosides showed lytic effect on MRSA cells.

Abstract

Galloylated flavonol rhamnosides identified as kaempferol-3-O-(2″,3″,4″-tri-O-galloyl)-α-l-rhamnopyranoside, quercetin-3-O-(3″,4″-di-O-galloyl)-α-l-rhamnopyranoside, and quercetin-3-O-(2″,3″,4″-tri-O-galloyl)-α-l-rhamnopyranoside, together with five known galloylated and non-galloylated flavonol rhamnosides, were isolated from leaves of Calliandra tergemina (L.) Benth. Their structures were established using spectroscopic methods and their antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA) were evaluated by a microdilution method.

Graphical abstract

Galloylated flavonol rhamnosides 13, together with five known flavonol rhamnosides, were isolated from a leaf extract of Calliandra tergemina. All metabolites were analysed for their potential anti-MRSA activities.

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Introduction

The genus Calliandra belongs to the family Leguminosae and subfamily Mimosaceae. The family has about 200 species of flowering plants native to tropical America, Madagascar and India. Several species are planted as ornamental plants (Mattagajasingh et al., 2006). There is, however, presently no paper describing the chemical constituents and bioactivity of Calliandra tergemina although there are reports on several related species including Calliandra portoricensis, Calliandra californica and Calliandra haematocephala (Aguwa and Lawal, 1988, Encarnacion et al., 1994, Agunu et al., 2005, Moharram et al., 2006 Orishadipe et al., 2010). Preliminary screening of the leaf extracts of C. tergemina displayed antibacterial activity against Micrococcus luteus, Bacillus cereus, methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA), respectively (Chew et al., 2011). The activity against MRSA is interesting as the latter is a major cause of infections in hospitals and resistant to all known beta-lactam antibiotics (Otsuka et al., 2008, Chew et al., 2011). Thus a bioassay-guided fractionation of C. tergemina leaf extracts, coupled with chromatographic separation; was employed to isolate the active constituents. This yielded three new galloylated flavonol rhamnosides and five known flavonol rhamnosides. This paper describes the isolation, structure elucidation and the structure–activity relationships of the isolated compounds.

Section snippets

Results and discussion

Five crude extracts were obtained from the leaves of C. tergemina of which the ethyl acetate extract had the highest anti-MRSA activity (Table 1); and from his extract, eight flavonol glycosides were isolated using a combination of silica gel column and gel filtration chromatography. Three new compounds were identified by their NMR (1H, 13C, HSQC, HMBC), UV and mass spectra, optical rotations, and by comparison with previously reported spectroscopic data. The five known galloylated and

Concluding remarks

Eight flavonol rhamnosides, including three new galloylated flavonol rhamnosides, were isolated from the leaves of C. tergemina. This is the first report on the phytochemical study of C. tergemina. The anti-MRSA activity of the extracts and isolated flavonol rhamnosides showed their structure–activity relationship where the esterification of the rhamnoside moiety was important in conferring anti-MRSA activity compared to the corresponding flavonol rhamnosides. There was no correlation between

General

Silica gel (Kieselgel 60, 70–230, and 230–400 mesh, Merck KGaA, Darmstadt, Germany), and Sephadex LH-20 (Pharmacia Fine Chemicals AB, Uppsala, Sweden) were used for column chromatography (CC). Optical rotations were measured on an Atago AP-300 automatic polarimeter. Ultraviolet (UV) absorption spectra were measured in MeOH using a HPLC with a UV/VIS detector separated by a C-18 reversed phase column (Assentis 25 cm × 4.9 mm × 5 μm). The HPLC profiles were processed with Agilent software to obtain the

Acknowledgements

The authors are thankful to Monash University Malaysia for financial support to EWLC for a visit to the Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde Glasgow for the use their NMR facilities and the University of Malaya Kuala Lumpur for LCMS analysis. We are grateful to Mr. Anthonysamy Savarimuthu (formerly of the University Putra Malaysia) for identifying the plant material.

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