The structure and synthesis of trimeric and related dimeric Proteracacinidins from Acacia heteroensis.
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Date
2002-07
Authors
Fourie, Eleanor
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University of the Free State
Abstract
English: The presence of 4', 7,8-trihydroxyl substituted flavanoids in plant material is limited to Acacia galpinii and Acacia caffra in Southern Africa. The existence of pyrogallol-type A-ring oligomers in these trees was for a long time believed not to be possible. During this investigation the presence of a number of dimeric and trimeric proteracacinidins in the heartwood of Acacia hereroensis were manifested and synthesized.
Column separations of the extract resulted in the enriched complex phenolic fractions which subsequently were derivatized and the compounds isolated as the methyl ether acetate derivatives. Extensive 1H and 13C (300 MHz) work, which entailed COSY, NOESY, HMQC and HMBC experiments were conducted to enable structure elucidations.
The monomeric leucoanthocyanidins epioritin-4α-ol, epioritin-4β-ol and oritin-4α-ol, are present in large quantities in the heartwood of A. hereroensis and were also accompanied by a variety of dimeric and trimeric proteracacinidins in lower concentrations. The two, by now well-known dimeric C-4 (C-ring) → C-6 (D-ring) linked compounds, e.g. epioritin-(4β →6)-epioritin-4α -ol and epioritin-(4β →6)-epioritin-4β-ol, were isolated.
The rare group of proteracacinidins with a C-4 (C-ring) → C-6 (D-ring) interflavanyl bond was extended with the isolation of ent-oritin-(4α →6)-epioritin-4α-ol, ent-oritin- (4β →6)-epioritin-4α -ol, epioritin-(4β →6)-oritin-4α-ol and the novel promela- /proteracacinidin dimer viz. epimesquitol-(4β →6)-epioritin-4α-ol. The C-4 (C-ring) → C- 4 (F-ring) ether linked dimer ent-oritin-(4α →4)-epioritin-4α -ol was isolated, together with the unique C-C and C-O-C linked trimer epioritin-(4β →3)-epioritin-(4β →6)- epioritin-4β-ol.
The difficult and sensitive synthetic approach during which the 4β-benzylthioether derivatives, epioritin-4β-benzylthioether and ent-oritin-4α -benzylthioether together with their corresponding underivatized monomers, e.g. epioritin-4β-ol and epioritin-4α-ol as nucleophiles in the presence of DMTSF as thiophilic Lewis acid were used to synthesize ent-oritin-(4α → 4)-epioritin-4α-ol and epioritin-(4β → 3)-epioritin-(4β →6)-epioritin-4β-ol, using different reaction conditions. The use of DMTSF and AgBF4 as thiophilic Lewis acid catalysts were tested with the successful synthesis of the two dimers, epioritin-(4β →6)-epioritin-4α-ol and epioritin-( 4β →6)-epioritin-4β-ol. Extensive use of these reactions were utilized to optimise the reaction conditions required during the other procedures.
Afrikaans: Die natuurlike voorkoms van 4' ,7,8-trihidroksie gesubstitueerde flavanoïede, in die Suid Afrikaanse konteks, is beperk tot Acacia galpinii en Acacia caffra. Daar is egter getwyfeloor die bestaan van oligomere met 'n pirogallol-tipe A-ring. Tydens hierdie ondersoek is 'n verskeidenheid dimeriese en trimeriese proteracacinidiene uit Acacia hereroensis geïsoleer en gesintetiseer. Kolom skeidings van die verrykte kernhout ekstrak het steeds onskeibare komplekse fenoliese mengsels gelewer en gevolglik is die metieleter asetaat derivate berei. Struktuur opklaring van die derivate is gedoen deur van massaspektrometrie en 1H KMR spektrometrie (300 MHz), 13C, COSY, NOESY, HMQC and HMBC eksperimente gebruik te maak. Afgesien van die monomeriese epioritin- 4α-ol, epioritin-4β-ol en oritin-4α-ol, het die kernhout van Acacia hereroensis ook 'n verskeidenheid dimeriese en trimeriese proteracacinidiene gelewer. Twee bekende C-4 (C-ring) → C-6 (D-ring) gebonde dimere, epioritin-(4β → 6)-epioritin-4α-ol en epicritin-(4β → 6)-epioritin-4β-ol, is geïsoleer. Die unieke groep proanthosianidiene met 'n C-4 (C-ring) → C-6 (D-ring) interflavaniel binding, is uitgebrei deur die isolasie van ent-oritin-(4α → 6)-epioritin-4α -ol, ent-oritin- (4β → 6)-epioritin-4α -ol, epioritin-(4β → 6)-oritin-4α -ol en die unieke promela- /proteracacinidien dimeer, epimesquitol-(4β→ 6)-epioritin-4α -ol. Die C-4 (C-ring) → C-4 (F-ring) eter gebonde dimeer ent-oritin-(4α → 4)-epioritin-4α -ol is ook geïsoleer, asook die C-C en C-O-C gebonde trimeer, epicritin-(4β → 3)-epioritin-(4β → 6)-epioritin-4β -ol. Die moeilike en delikate sintetiese benadering waartydens die 4β -bensieltioeter derivate, nl. epioritin-4β-bensieltioeter en ent-oritin-4α -bensieltioeter saam met die ooreenstemmende monomere, nl. Epioritin-4β-ol en epioritin-4α -ol as nukleofiel en DMTSF as tiofiliese Lewissuur gebruik is, het tot die sintese van ent-oritin-( 4α → 4)- epioritin-4α -ol en epioritin(4α → 3)-epioritin-(4α → 6)-epioritin-4β-ol gelei. Die sukses van DMTSF en AgBF4 as tiofiliese Lewissure is ook getoets, met die suksesvolle sintese van die bekende dimere, epioritin (4α → 6)-epioritin-4α -ol en epioritin-( 4α → 6)-epioritin- 4β-ol, en die optimisering van reaksie kondisies.
Afrikaans: Die natuurlike voorkoms van 4' ,7,8-trihidroksie gesubstitueerde flavanoïede, in die Suid Afrikaanse konteks, is beperk tot Acacia galpinii en Acacia caffra. Daar is egter getwyfeloor die bestaan van oligomere met 'n pirogallol-tipe A-ring. Tydens hierdie ondersoek is 'n verskeidenheid dimeriese en trimeriese proteracacinidiene uit Acacia hereroensis geïsoleer en gesintetiseer. Kolom skeidings van die verrykte kernhout ekstrak het steeds onskeibare komplekse fenoliese mengsels gelewer en gevolglik is die metieleter asetaat derivate berei. Struktuur opklaring van die derivate is gedoen deur van massaspektrometrie en 1H KMR spektrometrie (300 MHz), 13C, COSY, NOESY, HMQC and HMBC eksperimente gebruik te maak. Afgesien van die monomeriese epioritin- 4α-ol, epioritin-4β-ol en oritin-4α-ol, het die kernhout van Acacia hereroensis ook 'n verskeidenheid dimeriese en trimeriese proteracacinidiene gelewer. Twee bekende C-4 (C-ring) → C-6 (D-ring) gebonde dimere, epioritin-(4β → 6)-epioritin-4α-ol en epicritin-(4β → 6)-epioritin-4β-ol, is geïsoleer. Die unieke groep proanthosianidiene met 'n C-4 (C-ring) → C-6 (D-ring) interflavaniel binding, is uitgebrei deur die isolasie van ent-oritin-(4α → 6)-epioritin-4α -ol, ent-oritin- (4β → 6)-epioritin-4α -ol, epioritin-(4β → 6)-oritin-4α -ol en die unieke promela- /proteracacinidien dimeer, epimesquitol-(4β→ 6)-epioritin-4α -ol. Die C-4 (C-ring) → C-4 (F-ring) eter gebonde dimeer ent-oritin-(4α → 4)-epioritin-4α -ol is ook geïsoleer, asook die C-C en C-O-C gebonde trimeer, epicritin-(4β → 3)-epioritin-(4β → 6)-epioritin-4β -ol. Die moeilike en delikate sintetiese benadering waartydens die 4β -bensieltioeter derivate, nl. epioritin-4β-bensieltioeter en ent-oritin-4α -bensieltioeter saam met die ooreenstemmende monomere, nl. Epioritin-4β-ol en epioritin-4α -ol as nukleofiel en DMTSF as tiofiliese Lewissuur gebruik is, het tot die sintese van ent-oritin-( 4α → 4)- epioritin-4α -ol en epioritin(4α → 3)-epioritin-(4α → 6)-epioritin-4β-ol gelei. Die sukses van DMTSF en AgBF4 as tiofiliese Lewissure is ook getoets, met die suksesvolle sintese van die bekende dimere, epioritin (4α → 6)-epioritin-4α -ol en epioritin-( 4α → 6)-epioritin- 4β-ol, en die optimisering van reaksie kondisies.
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Keywords
Flavonoids, Anthocyanidins, Dissertation (M.Sc. (Chemistry))--University of the Free State, 2002