Chemical profile of walnuts (Juglans regia L.) and synthesis of stilbenes from Arformosia elata
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Date
2007-01
Authors
Sonopo, Molahlehi Samuel
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
Firstly, this study presents an in-depth investigation on Walnuts (the nuts of Juglans regia L.). Walnuts (Juglans regia L.) are members of the relatively small Juglandaceae family, which have shown positive results in humans, in the treatment of metabolic syndrome. Besides the very high content of unsaturated fatty acids (60-70%) in Walnuts (Juglans regia L.), previous investigations have revealed tannins as the only phenolics present. Generally, plants have had their biological activities attributed to the presence phenolics, specifically the flavonoids, which are the most abundant polyphenols in nature. Since Walnuts leave behind an astringent taste in the mouth after ingestion, a characteristic associated with presence of phenolics, especially tannins, it was reasonable to assume that Walnuts may also contain flavonoids. Besides having well-established biological activities such as, antioxidant, anticancer, and anti-inflammatory properties, flavonoids are believed to augment the ability of Walnuts to act as a possible candidate for treatment of metabolic syndrome. In the previous studies, isolation of flavonoids has not been reported. Therefore, in this study we carried out an in-depth investigation to establish the presence of flavonoids in the Walnuts Juglans regia L.
Pure compounds were obtained after repeated column and preparative thin layer chromatography and characterized by extensive NMR spectroscopic methods. The phenolics isolated in this study as peracetate and permethyl derivatives from the Walnuts Juglans regia L. are: catechin, gallocatechin, penta-O-acetyl-O-β-D-xylopyranosylellagic acid, gallic acid, methyl gallate, pedunculagin, casuarinin, hexaacetoxy-4-O-β-D-glucopyranosylnapthalene and 2,3-O-(S)-heptamethoxy-β-D-glucopyranosyldiphenoyl. Tetra-O-acetyl-9-β-D-glucopyranosylmegastigmen-3-one, tetraacetoxy-3-O-β-D-
glucopyranosylsitosterol, glucose and sucrose were isolated as non-phenolics.
Secondly, the study exploits methods to synthesize stilbene monomers and dimers isolated from Afrormosia elata. Afrormosia elata (Pericopsis elata) Harms, Fabaceae, is a tree native to the Guinean equatorial forests of West and Central Africa. The bark of this tree is used as a treatment for cancer by the local population. Stilbenes are a class of polyphenols with very
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limited taxonomic distribution and varied biological activities which include, blood sugar reduction, antibacterial, antifungal, antioxidant, anti-HIV and anti-inflammatory. They posses COX-1 and COX-2 inhibitory effects, affect lipid peroxidation, LDL oxidation, function as phytoalexins, and have chemopreventative effects on cancer. The reported biological activities of stilbenes highlight the importance of stilbenoids as a resource for development of new drugs and pesticides. Since the occurrence of these stilbenoids in plants is in extremely low concentrations, we attempted synthesis of dimeric stilbenes with the aim of developing methods which may yield qualitative amounts. Syntheses of the monomeric stilbenes preceded that of the dimers. The classic Wittig reaction and the most recently developed metathesis reactions were the routes used to synthesize the monomers,while the route via the Heck coupling was considered for synthesis of the dimeric stilbenes.
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Keywords
Isolation, Dimers, Stilbenes, Monomers, Dissertation (M.Sc. (Chemistry))--University of the Free State, 2007, Plant polyphenols, Tannins, Walnut, Structural elucidation, Hydrolysable tannins Juglans regia L. synthesis, Grubbs catalyst, Heck reaction