Masters Degrees (Chemistry)
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Browsing Masters Degrees (Chemistry) by Author "Brand, D. J."
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Item Open Access Structure and synthesis of polyphenols from cyclopia subternata(University of the Free State, 2002-06) Brand, D. J.; Brandt, E. V.; Kamara, B. I.English: Cyclopia subternata (Fabaceae), from which Honeybush tea is brewed, is one of approximately 24 Cyclopia species of woody legumes endemic to the Cape fynbos (Cape macchia) region of South Africa. Supported by results from our initial investigations on C. intermedia, demonstrating the presence of phenolic compounds including coumestans, isoflavones, flavanones, xanthones, a flavone, pinitol, p-coumaric acid and flavonoid glycosides, the tea is gaining popularity as a health beverage. Presence of these compounds that are claimed to have interesting pharmacological properties, supported by belief that the tea contains very little, if any, caffeine and low tannin content, as well as its usage as a medicinal plant by the people of the Western and Eastern Cape prompted investigations on the subternata species. The acetone and methanol extracts of the unfermented shoots and stems of C. subternata were subjected to chromatographic separations (Shephadex LH-20 column and preparative thin layer) which afforded a novel flavan, flavonols, flavanones, flavones, isoflavone and C6.C2- and C6.C1-type compounds. Their full acetate or methylated derivatives were elucidated and characterized by high resolution (300 MHz) ¹H NMR speetrometry which included COSY, NOESY, HMQC, HMBC, DEPT 135° experiments and ¹³C NMR spectroscopy, Molecular Modeling and Circular Dichroism. Along with (+)-Pinitol a novel apiofuranosyl (1"—›6')-glucopyranosyl carboxylic acid was isolated as a non-flavonoid compound. The flavonoid aglycones isolated included epicatechin-3-0-gallate (flavanol), luteolin (flavone) and orobol (isoflavone). The nonflavonoid glycosides included a 4-0-gl ucopyranosyl tyrosol, apiofuranosyl (l"—›6')- glucopyranosyl benzaldehyde and the acetate derivatives of two new O-glycosides namely 1-[(β-D-2',3' ,4' -tri-O-acetylglucopyranosyloxy ]-2-(3,5-diacetoxyphenyl)ethane and l-acetoxy-2-(β-D-2',3',4',6' -tetra-O-acetylglucopyranosyloxy)ethane. The flavonoid O-glycosides comprised a novel 3',4',7-trihydroxy-5-(glucopyranosyloxy) flavan, the flavone, scolymoside and the flavanones, hesperedin, narirutin and eriocitrin. C-glycosides isolated includes the xanthone, mangiferin, a C-6-glycosylated kaempferol as well as two new C-glycosides, 3,4' ,6, 7-tetrahydroxy-5-W-D-glucopyranosyl) flavonol and 3' ,4',5,5', 7-pentahydroxy-8-(β-D-glucopyranosyl) flavanone. Due to the novelty and the many proposed health properties of flavans, the relatively unexplored routes to flavonoid O-glycosylation and the effects of glycosylation on the aglycone solubility and general behaviour, including the absorption in tissues of man, prompted the synthesis of the isolated flavan glycoside. The uncertainty of the point of sugar attachment to the aglycone of some glycosides, especially with limited material available, further inspired the exploration of synthetic routes to glycosylated flavonoids. In an attempt to obtain the 5-O-glycosylated flavan, the selected glycosylation procedure was attempted on the analogous 5,7-dihydroxy-3',4'-dimethoxyflavanone, but proved unsuccessful because of the acidity of the 3-protons leading to ring opening. The same, procedure was attempted on the analogous chalcone with an unprotected A-ring. Glycosylations was successfully done on resacetophenone, phloroacetophenone and 4- methoxyphloroacetophenone as precursors to the formation of the glycosylated chalcone. However, the condensation with the appropriately protected benzaldehyde to obtain the glycosylated chalcone as precursor to the 5-O-glycosylated flavan was unsuccessful. The proposals that phenolic metabolites have physiological and therapeutic properties may also be associated with the compounds isolated from the tea. Luteolin and eriodictyol constitute part of the phenolic metabolic pool with a 3',4' -diol functionality which is claimed to have antioxidant activity. The antimicrobial activity of flavonoids in plants is also well documented and so is the antiviral activity of flavonoids and their ability to inhibit key enzymes in mitochondrial respiration. It was found that a C-2, C-3- double bond, a 4-keto group and a 3',4',5' -trihydroxylation of the B-ring are significant features of those flavonoids which show strong inhibition of NADH-oxidase. Coronary heart disease is also reported to be reduced in humans with high flavonoid intake. The anti-inflammatory and antitumor activity along with the ever-increasing interest in plant tlavonoids for treating human diseases and especially for controlling the immunodeficiency virus, the cause of AIDS, also attract interest in this herbal tea. These results clearly indicate that the claims of the health promoting properties of Honeybush tea may at least, in part, be attributed to the presence of these and other polyphenols in C. subternata.