Masters Degrees (Chemistry)
Permanent URI for this collection
Browse
Browsing Masters Degrees (Chemistry) by Author "Brandt, E. V."
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item Open Access Die eerste oligomeriese neoflavonoiede: struktuur en sintese van modelverbindings(University of the Free State, 1993-05) Nel, Janetta Wilhelmina; Bezuidenhoudt, B. C. B.; Brandt, E. V.; Ferreira, D.Afrikaans: Hoewel oligomeriese flavonoïede reeds etlike dekades bekend is, is die eerste bi-isoflavonoïede eers onlangs uit Dalbergia spesies geïsoleer en is oligomere saamgestel uit neoflavonoïede nog onbekend. Ten einde die poel van oligomeriese isoflavonoïede uit te brei is die fitochemiese ondersoek na die fenoliese komponente in die kernhout van Dalbergia nitidula Welw. ex Bak, bekend vir die voorkoms van talle monomeriese iso- en neoflavonoïede, onderneem. Drie nuwe unieke iso-neoflavonoïed dimeriese verbindings bestaande uit 'n seldsame 3-fenielbenso[b]furaan- en vir die eerste keer 'n pterokarpaaneenheid, nl. (6aS,11aS)-2-, (6aS,11aS)-4- en (6aS,11aS)-8-[3-feniel-5-hidroksi-6-metoksibenso-[b]furan-2-ielmetiel]medikarpin, is inderdaad tydens die ondersoek gevind. Hierdie verbindings word in die eterekstrak vergesel deur 'n verdere dimeer waarin dieselfde neoflavonoïedeenheid aan (+ )-vestitol gebind is, nl. (3S)-8-[3-feniel-5-hidroksi-6-metoksi benso[b]furan-2-ielmetiel] vestitol. Benewens die dimere is 2', 7-dihidroksi-4'-metoksi-isoflav-3-een, die vyfde natuurlike isoflaveen, en (6aS,11aS)-2-hidroksi-3,9-dimetoksipterokarpaan as nuwe mono-mere verkry, terwyl 3,8-dihidroksi-9-metoksipterokarpaan vir die eerste keer as die 6aS,11aS isomeer geïsoleer is. Die bekende benso[b]furaan, centrolobofuraan, is ook saam met bekende verbindings soos (±)-ferreirien, di-O-metieldaidzein, (+ )-claussekinoon, 3-hidroksi-9-metoksikumestaan en (+ )-vestikarpin vir die eerste keer in hierdie spesie gevind, terwyl (+ )-medikarpin, (+ )-homopterokarpin, (+ )-vestitol, 3,9-dimetoksikumestaan asook (±)-liquiritigenien en isoliquiritigenien weereens verkry is. Aangesien onsekerheid omtrent die heterosikliese sisteem van die neoflavonoïedeenheid in die dimere bestaan het, is die sintese van 'n neoflavonoieddimeer met 'n seslid heterosikliese ring, (6 aS,11as)-4-[6-hidroksi-7 -metoksineoflav-3-een-3-iel] medikarpin d.m.v. 'n aldol-tipe kondensasie tussen 'n gesubstitueerde bensofenoon en pterokarpanielasetaldehied gevolg deur 'n sikliseringstap, aanvanklik aangepak (Skema). Weens die seldsame substitusiepatroon van die bensofenoon, is 2-hidroksi--4-metoksibensofenoon, as model, d.m.v. 'n Grignardreaksie tussen 4-metoksi-2-O-metoksimetielbensaldehied en fenielmagnesiumbromied daargestel en die pterokarpanielasetaldehied vanaf (+ )-medikarpin deur O-allilering (K2C03/ asetoon/ allielbromied) gevolg deur Claisenherrangskikking (N,N-dimetielanilien) en oksidatiewe splyting (OsO4/N-metielmorfolien-N-oksied gevolg deur NaIO4/MeOH) van die allielgroep, in 14% opbrengs verkry. Intermolekulêre aldolkondensasie (LDA/THF of asynsuur /H2S04) tussen die ptero-karpanielasetaldehied en die bensofenoon kon egter nie bewerkstellig word nie. Ten einde 'n Von Pechman-tipe kondensasie vir die sintese te kan benut moes die pterokarpanielasetaldehied na die ooreenstemmende suur geoksideer word, maar ten spyte van die aanwending van 'n verskeidenheid reagense (piridiniumdichromaat; RuCl3; Tollensreagens; KMn04; Ag20) kon 2-O-etoksimetiel-4,6-dimetoksifenielasetaldehied, as model, nie in noemenswaardige opbrengs na die ooreenstemmende suur geoksideer word nie. A.g.v. die onvermoë om die verlangde pterokarpanielasynsuur daar te stel, is die sintese van 'n model van die neoflavonoïedeenheid, 3-feniel-7-metoksineoflav-3-een, aangepak en is verestering van 2-hidroksi-4-metoksibensofenoon met fenielasetielchloried (K2C03/ asetoon) gevolg deur intramolekulêre siklisering (K2C03/ asetoon) en reduksie van die laktoonfunksionaliteit (B2H6THF) uitgevoer (10% opbrengs). Vergelyking van die chemiese verskuiwing van die CH2Sein in die 1H-KMR-(8 5.09) sowel as 13C-KMR-spektra (8 69.8) met dié van die natuurprodukte (8 4.13 - 4.24 en 8 21.0 onderskeidelik) het egter ondubbelsinnig getoon dat die natuurlike verbindings nie 'n seslid-heterosikliese ring in die neoflavonoïedeenheid bevat nie. Ten einde soortgelyke KMR-vergelyking vir die struktuur met die benso[b]furanielneoflavonoïed te doen, is voortgegaan met 'n modelsintese vir hierdie sisteem en is die verlangde 2-bensiel-3-fenielbenso[b]furaan d.m.v. Friedel-Grafts asilering van resorsinol met chloroasetielchloried, gevolg deur bensilering (bensielbromied, K2C03/asetoon) en Grignardreaksie van die gevormde bensofuranoon met fenielmagnesiumbromied daargestel. Hoewel presiese ooreenstemming in chemiese verskuiwing (8 4.17 en 8 32.8 onderskeidelik in die 1H- en 13C-KMR-spektra) van die metileengroep tussen die gesintetiseerde model en die natuurproduk nie verkry is nie, is dit aan verskille in struktuur en substitusiepatroon toegeskryf en kan 'n benso[b]furaanstruktuur aan die neoflavonoïedeenheid toegeken word.Item Open Access Polyphenols from pericopsis elata and synthesis of selected stilbenes(University of the Free State, 2005-05) Litedu, Eunice Maria; Kamara, B. I.; Brandt, E. V.English: The bark of Pericopsis elata (Afrormosia elata) is used by the local population of the Democratic Republic of Congo for the treatment of cancer and for external applications because of its weather resistance. Previous phytochemical studies on Pericopsis elata resulted in the isolation of flavonoids, isoflavonoids, chalcones and stilbene monomers. Among these, stilbenes are known to have biological activities such as antioxidants, antifungal, and act as microbial inhibitors. They posses COX-1 and COX-2 inhibitory effects, affect lipid peroxidation, LDL oxidation, and function as phytoalexins among other activities. Prompted by these claims, we conducted an in depth investigation of the heartwood of P. elata by extraction, isolation and structural elucidation of the metabolites. The enrichment and fractionation of monomeric and dimeric constituents were accomplished mainly by Craig countercurrent distribution techniques and Sephadex LH-20 gel chromatography. Pure compounds were obtained by derivatization and preparative thin layer chromatography. Structural elucidation of the phenolics is based mainly on NMR spectroscopic methods (1H NMR, 13C NMR, COSY, NOESY, HMBC and HMQC), Mass spectrometry and synthetic methods.The monomeric compounds isolated during this study comprise the flavanones (naringenin and eriodictyol), the isoflavones (genistein and biochanin A), a dihydrochalcone [(R)-α,4,2',4'-tetraacetoxydihydrochalcone] and a single α- methyldeoxybenzoin (angolensin). Among the stilbene monomers encountered are resveratrol, isorhapontigenin and large amounts of piceatannol. Structures of the dimeric stilbnes isolated apparently originate from different combinations of piceatannol (3,4,3',5'-tetrahydroxystilbene) (the major constituent ~ 16% of the phenolic content of P. elata) and 3,4,3',4'-tetrahydroxystilbene. To the best of our knowledge rel-2,3-trans-2-(3,4-dimethoxyphenyl)-3-(3,5-dimethoxyphenyl)-6-[2-(3,5- dimethoxyphenyl)-E-1-ethenyl]benzodioxane, rel-2,3-trans-2-(3,4-dimethoxyphenyl)-3- (3,4-dimethoxyphenyl)-4-[2-(3,4- dimethoxyphenyl) )-E-1-ethenyl]-6-methoxy-2,3- dihydrobenzofuran, rel-2,3-trans-2-(3,4-diacetoxyphenyl)-3-(3,5-diacetoxyphenyl)-4-[2- (3,4-diacetoxyphenyl) )-E-1-ethenyl]-6-acetoxy-2,3-dihydrobenzofuran, rel-2,3-trans-2- (3,4-dimethoxyphenyl)-3-(3,5-dimethoxyphenyl)-4-[2-(3,5-dimethoxyphenyl) )-Z-1- ethenyl]-6-methoxy-2,3-dihydrobenzofuran, rel-2,3-trans-4-Formyl-2-(3,4- dimethoxyphenyl)-3-(3,5-dimethoxyphenyl)- 6-methoxy-2,3-dihydrobenzofuran and rel- 2,3-trans-2-(3,5-diacetoxyphenyl)-3-(3,5-diacetoxyphenyl)-6-[2-(3,5-diacetoxyphenyl) )- E-1-ethenyl]-4-acetoxy-2,3-dihydrobenzofuran are novel compounds. Structural confirmation of the six novel dimeric stilbenes in particular required definition of structure via synthetic methods. A synthetic approach was thus developed. This protocol comprises the synthesis of piceatannol via the Wittig reaction followed by oxidative coupling of two piceatannols to afford novel dimeric stilbenes. 1H NMR of the methoxy-derivative of synthetic compounds is identical to that of the derivative of two dimeric stilbenes isolated from P. elata.Item Open Access Sintese en struktuur van Pirano-isoflavanoïede(University of the Free State, 1977-01) Van Heerden, Fanie Retief; Roux, D. G.; Brandt, E. V.Afrikaans: Die medisinale gebruik (waarskynlik as antiseptikum) van die bas van Dalbergia nitidula Welw. ex Bak. (Leguminosae) deur inboorlinge het tot die huidige chemiese ondersoek aanleiding gegee. Hierdie ondersoek behels dus die isolering en struktuuropklaring van vier nuwe, natuurlike isoflavane, naamlik leiocin, nitidulin, nitidulan en heminitidulan, asook drie nuwe pterokarpaan-analoë waaraan die benamings nitiducarpin, hemileiocarpin en nitiducol toegeken is. ‘n Verdere nuwe isoflavaan, leiocinol se struktuur kon slegs gedeeltelik opgeklaar word, terwyl die isolasie van leiocarpin, 'n bekende pterokarpaan, 'n gerieflike verwysingselement in die stereochemiese opklaring van die pterokarpane daargestel het. Ter bevestiging van die strukture van die isoflavane, is 'n totaalsintese van 2'-0--metielleiocin uitgevoer. Die stereochem ie by C-3 van die isofLavane is met behulp van SD-kurwes as 3S bepaal, terwyl dié van die pterokarpane 6aS, llaS blyk te wees. Stereochemiese ekwivalensie by 'n enkele chiralsentrum, naamlik C-3 I van isoflavane en die ooreenstemmende C-6a van pterokarpane, dui op 'n gemeenskaplike biogenetiese oorsprong van hierdie twee tipes verbindinge. Substitusiepatrone van die metaboliete toon 'n noue verwantskap, in ooreenstemming met biogenetiese oorwegings. Die verbindings, met uitsondering van nitiducol, bevat deurgaans 'n addisionele 2H-piraanring aan die A-ring van die isoflavanoïedskelet. In verskeie gevalle is die. 2H-piraanring konvensioneel 2,2-dimetiel-gesubstitueerd (leiocin, leiocinol, hemileiocarpin), terwyl dit in ander gevalle 'n interessante en seldsame 2-metiel-2-(4-metiel-3-penteniel) substitusiepatroon besit (nitidulin, nitidulan, heminitidulan, nitiducarpin). Nitiducol, 'n pterokarpaan, bevat 'n geranielsyketting en orto-hidroksigroep as substituente, wat in die gesikliseerde isomeer deur die 2-metiel-2-(4-metiel-3-penteniel)-2H-piraanring (nitiducarpin) verteenwoordig word. Die voorlopige struktuur van die isoflavaan, leioeinol, is onderhewig aan verdere bevestiging deur totaalsintese. Ter ondersteuning van die strukture van ‘n aantal verwante isoflavane is 'n totaalsintese van 2'-O-metielleiocin uitgevoer. Aanvanklik is gepoog om leiocin via die ooreenstemmende chalkoon en isoflavoon te berei, maar die sintese kon vanweë swak isoflavoonvorming in die teenwoordigheid van die vry hidroksifunksie nie voltooi word nie. 2'-0-Metielleiocin is egter suksesvol gesintetiseer en die produk is identies aan die 2'-0- metieleter van die ooreenstemmende natuurproduk bevind. 'n Totaalsintese van die oorblywende metaboliete, sowel as 'n ondersoek na die anti-patogene en medisinale eienskappe van die verbindings word in die vooruitsig gestel.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.