Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/14/2010
Publication Date: 10/1/2010
Citation: Ma, C., Whitaker, B.D., Kennelly, E. 2010. New 5-O-caffeoylquinic acid derivatives in fruit of the wild eggplant relative Solanum viarum. Journal of Agricultural and Food Chemistry. 58:11036-11042. Interpretive Summary: Fruit of eggplant and its wild relatives are rich in antioxidant chemicals that are potentially beneficial to human health. In most eggplant lines, these so-called nutraceuticals are made up of a small number of known compounds, but in a few wild relatives there is an abundance of rare and/or unknown compounds that may have novel beneficial biological activity. A group of four such previously unidentified antioxidant compounds was isolated from fruit of one wild eggplant species and their structures were elucidated. This will enable future testing of these natural chemicals as chemopreventive agents that block or delay the advent of chronic diseases. The long-range goal of this work is to develop new commercial eggplant lines bearing fruit with a broader array of nutraceuticals that combat various cancers and cardiovascular disease.
Technical Abstract: Fruit of cultivated eggplant (Solanum melongena) and several wild relatives (S. aethiopicum, S. macrocarpon, S. anguivi, and S. incanum) have a high content of hydroxycinnamic acid (HCA) conjugates. Typically, caffeoylquinic acid esters predominate, and in particular chlorogenic acid [5-O-(E)-caffeoylquinic acid; 5-CQA]. By contrast, fruit from one accession of S. anguivi in the USDA eggplant core collection (PI 319855) were found to include several major, closely related HCA conjugates with much longer C18-HPLC retention times than those of 5-CQA and other mono-CQA isomers. Four of these compounds were isolated from methanolic extracts of lyophilized fruit tissues by C18-HPLC, and structurally elucidated using HR-ESI-MS and 1H- and 13C-NMR techniques. The simplest structure, from which the other three are derived, is composed of 5-CQA plus a 6-O-sinapoylglucose group 1-O-beta-linked with the 4 hydroxyl on the phenyl ring of the caffeoyl moiety (compound 3; 1,3-beta,4-beta-trihydroxyl-5-alpha-[[3-[4-[1-beta-(6-O-(E)-sinapoyl-beta-D-glucopyranosyl)oxy]-3-hydroxyphenyl]-(E)-1-oxo-2-propenyl]oxy]cyclohexanecarboxylic acid). Compound 4 differs from 3 by methylation of the carboxyl group on quinic acid, while isomeric compounds 1 and 2 differ from 3 by malonation of the 3 or 4 hydroxyl group, respectively, on quinic acid. Some features of these four compounds, such as malonation and the specific linkages between caffeoyl, glucosyl, and sinapoyl moieties, are common in acylated and glycosylated phenylpropanoids, but have not previously been reported in complex derivatives of chlorogenic acid.