Zur Kenntnis der Proanthocyanidine, X Procyanidine aus Früchten

Abstract

Die von uns aus Fruchten isolierten Procyanidine zerfallen beim Erwarmen mit Sauren in Cyanidin und Catechin bzw. Epicatechin. Sie sind demnach als dimere Flavonoide mit einem Kohlenstoffgerust von 30 C-Atomen aufzufassen. Nach der Anzahl der Wasserstoffatome werden sie in zwei Gruppen der Summenformel C30H26012 (Gruppe B) und C30H24012 (Gruppe A) eingeteilt. Innerhalb dieser Gruppen sind sowohl Struktur-als auch Stereoisomere denkbar. Die Konstitutionen der beiden Procyanidin-Gruppen werden an Hand NMR-und massenspektrometrischer Untersuchungen ihrer Derivate diskutiert. Zum Vergleich wurden Modellsubstanzen synthetisiert.Proanthocyanidineaus zwei Flavonoid-Einheiten aufgebautsind in Friichten sehr weit verbreitetz-11). Sie lassen sich durch Erwarmen mit Sauren nachweisen, wobei das Molekiil unter Anthocyanidinbildung gespalten wird. Man unterscheidet nach dem erhaltenen Anthocyanidin zwischen Propelargonidinen, Procyanidinen und 1) Die folgenden Literaturangaben gelten als vorhergehende Mitteilungen dieser Reihe:

Heterogeneity of interflavanoid bond location in loblolly pine bark procyanidins

“…showed an epicatechin-catechin dimer (Table I) and chemical shifts consistent with those reported for procyanidin B-1 [2]. Benzenethiol degradation followed by methylation gave [7]. procyanidin B-3 (2) was obtained in fractions 196-230 together with small impurities of the procyanidin B-1.…”

Dimeric prodelphinidins from Limonium gmelinii roots. III.

“…The bond also does not involve the side phenyl rings because two 2H singlets were recorded at δ 7.20 (ring B) and 7.00 ppm (ring E). This was confirmed by peaks in the mass spectrum of the monoacetylpermethyl ether of 5 with m/z 714 that formed through cleavage of an acetate and gallic acid from C-3 of both halves of the molecule and with m/z 404 and 181 that were characteristic of trimethoxy derivatives of the side phenyls [9,26]. The appearance in the spectrum of signals for protons of a single methylene instead of two argued in favor of an interflavan bond at C-4.…”

Proton magnetic resonance spectra of catechin and bromocatechin derivatives: C6- vs. C8-substitution

“…Ever since the isolation and structure elucidation of the first dimeric procyanidins by Weinges et al (1) and their first synthesis (2,3), unambiguous determination of the position of the interflavanoid linkage, i.e., the carbon atom of ring A of the terminal catechin or epicatechin unit (C-6 or C-8) that is bonded to C-4 of a second flavanoid, has remained problematic. This applies even to simple monoflavanoids such as monobromotetra-and penta-0-methylcatechin, for which Weinges (1,3) postulated the 8-bromo structure on the basis of the greater steric accessibility of C-8 relative to C-6 in electrophilic aromatic substitution.…”

“…This applies even to simple monoflavanoids such as monobromotetra-and penta-0-methylcatechin, for which Weinges (1,3) postulated the 8-bromo structure on the basis of the greater steric accessibility of C-8 relative to C-6 in electrophilic aromatic substitution. It was not until 1977 (4) and 1985 (5) that the configurations of 8-bromo-3',4',5,7-tetra-0-methylcatechin (3d) and 6-bromo-3,3 ' ,4' ,5,7-penta-0-methylcatechin (4c) were proven by X-ray structure analysis.…”