Systematic Phytochemistry of Legumes
Research to discover and describe the compounds produced by legumes is being undertaken in a systematic framework to provide characters to test new phylogenies and to support the sustainable use of legumes.
Analysing legume extracts using LC-MS
Leguminosae produce a diverse array of secondary metabolites. For this reason, and in view of the economic importance of the family, the phytochemistry of legumes has been investigated intensively. Historically, the systematic occurrence of various chemicals in legumes has been interpreted within the traditional concepts of legume classification based mostly upon morphological characters. Now, with the analysis of DNA sequences providing new hypotheses on relationships for a wide range of legume genera, it is possible to re-examine existing phytochemical data and obtain new data within the context of current ideas of legume systematics.
The Systematic Phytochemistry of Legumes project covers two main areas. One is to undertake phytochemical investigations on relationships revealed by the new arrangement of legume genera outlined in Legumes of the World and subsequent phylogenies. An emphasis in recent years has been genera currently classified in the tribes Sophoreae and Swartzieae of subfamily Papilionoideae which comprise an unnatural assemblage, with several genera having closer affinities with other legume tribes and generic groupings than with core Sophoreae and Swartzieae. For example, in Sophoreae detailed chemical studies to examine the suggested relationship between Cladrastis and Styphnolobium revealed 16 flavonoids new to science with some common to both taxa (Kite et al., 2011). In Swartzieae, novel non-protein amino acids and flavonoids have provided informative characters in a multi-disciplinary phylogenetic analysis of Ateleia (Ireland et al.,, 2010), while structural features of two previously unreported flavonoids discovered in Cordyla supported a proposed relationship with Milbraediodendron (Veitch et al., 2008), and argued against the transfer of two species of Cordyla to the new genus Dupuya.
The second and more recent area that is being covered by the project is the systematic phytochemistry of economically important legumes, linking closely with projects on the ‘Importance of Legumes and Legume-Derived Compounds in Medicine and Agriculture’ and the project on the ‘Authentication and Chemical Fingerprinting of Economically Important Species’. These studies focus on particular species of economic value and their close relatives. Examples of recent outcomes are the discovery of a chemical marker for Brazilian Rosewood (timber of Dalbergia nigra) to assist enforcement of CITES regulations (Kite et al., 2010) and the authentication of the Chinese herbal medicine ingredient Fructus Sophorae (fruits of Styphnolobium japonicum) (Kite et al., 2009).
Both project areas employ similar methodologies. Detailed phytochemical characterisation is performed on key species of systematic or economic interest through the isolation of compounds and their structural elucidation, by in-house NMR spectroscopy. Compounds of relevance to systematic or economic use are then surveyed to establish their occurrence in related taxa. Modern analytical techniques, such as the combination of high performance liquid chromatography with mass spectrometry (LC-MS), have meant that only small fragments of material are needed to perform these surveys. In some studies this opens up the possibility of examining material from Kew’s extensive herbarium legume collections with minimal impact on specimens.
Key publications 2006-2011
- Ireland, H.E., Kite, G.C., Veitch, N.C., Chase, M.W., Schrire, B., Lavin, M., Linares, J. & Pennington, R.T. (2010) Biogeographic, ecological, and morphological structure in a phylogenetic analysis of Ateleia (Swartzieae, Fabaceae) derived from combined molecular and morphological/chemical data. Botanical Journal of the Linnean Society 162, 39–53.
- Kite, G.C., Green, P.W.C., Veitch, N.C., Groves, M.C., Gasson, P.E. & Simmonds, M.S.J. (2010). Dalnigrin, a neoflavonoid marker for the identification of Brazilian rosewood (Dalbergia nigra) in CITES enforcement. Phytochemistry 71: 1122–1131.
- Kite, G.C., Rowe, E.R., Lewis, G.P. & Veitch, N.C. (2011). Acylated flavonol tri- and tetraglycosides in the flavonoid metabolome of Cladrastis kentukea (Leguminosae). Phytochemistry 72: 372-384.
- Kite, G.C., Veitch, N.C., Boalch, M.E., Lewis, G.P., Leon, C.J. & Simmonds, M.S.J. (2009). Flavonol tetraglycosides from fruits of Styphnolobium japonicum (Leguminosae) and the authentication of Fructus Sophorae and Flos Sophorae. Phytochemistry 70: 785–794.
- Veitch, N.C., Kite, G.C. and Lewis, G.P. (2008). Flavonol pentaglycosides of Cordyla (Leguminosae: Papilionoideae: Swartzieae): Distribution and taxonomic implications. Phytochemistry 69: 2329-2335.
Project partners and collaborators
Technical University of Munich
Annex 1: Trace from liquid chromatography-mass spectrometry (LC-MS) of a small fragment of material of Bocoa mollis (Swartzieae) from RBG Kew’s Herbarium collections. (Word document)
Annex 2: Structure of Milbraedin, a new and unusual flavonoid glycoside isolated from the leaves of Mildbraediodendron excelsum (Swartzieae) following detailed phytochemical investigation of material in the living collections of RBG Kew. (Word document)