Oxydative Kupplung von Phenolen, III¹⁾ Isolierung und Konstitutionsbeweis eines 8.6′‐verknüpften Dehydro‐dicatechins (B4)

Abstract

Bei der enzymatischen Dehydrierung des (+)-Catechins lassen sich neben dem Dehydro dicatechin A (C30H24012) vier weitere Dehydro-dicatechine B1 -B4 (C30H26012) und ein Dehydro-tricatechin isolieren. Die Dehydro-dicatechine B1 -B4 sind mit den Procyanidinen der Gruppe B isomer. Die Konstitution des Dehydro-dicatechins B4 (l), aus dem durch weitere Oxydation das Dehydro-dicatechin A entstehen sollte, wird mit Hilfe der NMR-und Massenspektren des Diacetyloctamethyl-Derivats 4 bzw. des Octamethyl-Derivats 3 bewiesen. Oxydative Coupling of' Phenols, III1). Isolation and Constitution of a Dehydro-dicatechin (B4) Linked in the 8,6-PositionEnzymatic dehydrogenation of (+)-catechin affords besides dehydro-dicatechin A (C30H24012) four additional dehydro-dicatechins B1 -B4 (C30H26012) and a dehydro-tricatechin. The dehydro-dicatechins Bl -B4 are isomeric with the procyanidins of the B group. The constitution 1 of dehydro-dicatechin B4 is proved by means of N M R and mass spectroscopic analysis of its diacetyloctamethyl derivative 4 and of its octamethyl derivative 3.Das von uns beschriebene Dehydro-dicatechin A1) fallt wegen seiner Schwerloslichkeit in Wasser wahrend der enzymatischen Dehydrierung des ( +)-Catechins fast vollstandig aus der Dehydrierungslosung aus. In Losung verbleiben neben Polymeren noch vier weitere Dehydro-dicatechine, die wir mit B 1 -B4 bezeichnen. Ferner tritt noch in geringer Menge ein Dehydro-tricatechin auf. Die Dehydro-dicatechine B 1 -B4 (Summenformel : C30H26012) unterscheiden sich vom Dehydro-dicatechin A (C30H24012) durch zwei zusatzliche Wasserstoffatome.Die Dehydro-dicatechine A und B sind demnach isomer mit den entsprechenden Gruppen der Procyanidine 2 ) , die aus Friichten isoliert wurden, verhalten sich aber 1) 11.

Characterization of procyanidin B2 oxidation products in an apple juice model solution and confirmation of their presence in apple juice by high‐performance liquid chromatography coupled to electrospray ion trap mass spectrometry

“…It can be noted that these compounds are also A-type dehydrodicatechin isomers resulting from oxidative coupling between two catechin molecules. [44,46] Numerous peaks were clearly detected in the EIC (Fig. 10B) at m/z 575.…”

“…, hypothesis II). The ether‐linkage involving carbon 6' is probably favored as observed for dehydrodicatechins and oxidation products resulting from coupling between the catechol ring and the phloroglucinol ring of two catechin moieties …”

“…The cider apple juice was firstly screened for the presence of A‐type procyanidin dimers [M‐H] − at m/z 575, as previously for the model solutions. It can be noted that these compounds are also A‐type dehydrodicatechin isomers resulting from oxidative coupling between two catechin molecules …”

“…The ether-linkage involving carbon 6' is probably favored as observed for dehydrodicatechins and oxidation products resulting from coupling between the catechol ring and the phloroglucinol ring of two catechin moieties. [44][45][46] The MS/MS spectra of the oxidation products ([M-H] À at m/z 573), (1) at 6.0 min and (4) at 10.2 min were very different ( Table 1). The MS/MS fragmentation patterns and structural hypotheses for product (4) Unfortunately, the MS/MS fragmentation pattern did not enable the two structural hypotheses showing C5-O-C6' or C5-O-C2' linkages to be differentiated (Fig.…”

UPLC‐ESI‐MS study of the oxidation markers released from tannin depolymerization: toward a better characterization of the tannin evolution over food and beverage processing

“…The radical semiquinone may be the first product arising from oxidation of the phenolic compound or may result from a comproportionation process between an ortho‐quinone molecule and the corresponding catechol. The radical coupling between two semiquinones or the Mickael‐type addition of the A‐ring of an (epi)catechin molecule onto the orthoquinone moiety of another (epi)catechin molecule leads to colourless oxidized dimers that are usually referred to as dehydrodicatechin B with C–C or C–O biaryl interflavanic linkage and contain at least one catechol ring. These oxidation products can be further oxidized into yellow pigments that are usually referred to as dehydrodicatechin A …”