GERALD OLIVER ASPINALL, DELPHI CHATTERJEE, and LEV KHONDO. Can. J . Chem. 62, 2728Chem. 62, (1984. The Bernet-Vasella reaction of 6-deoxy-6-halohexopyranosides with zinc dust to give hex-5-enoses has been explored as the basis for a new procedure for the selective cleavage of glycosidic linkages in complex oligo-and polysaccharides. The overall reaction sequence involves: (a) the generation of primary hydroxyl groups in otherwise fully methylated oligo-or polysaccharides; (b) the formation of 6-deoxy-6-iodohexopyranosides by iodide displacement of reactive sulfonate esters; and (c) treatment with zinc dust followed by the formation of suitable derivatives from the liberated hex-5-enoses. Oligosaccharides carrying P-D-xylopyranosyl substituents at the 2-0-(4), 3-0-(17), 4-0-(12), and both 3-0-and 4-0-(8) positions have been converted into otherwise fully methylated derivatives, each containing methyl 6-deoxy-6-iodo-a-D-galactopyranoside residues, to serve as model substrates for different structural environments. In each case the derived 5,6-dideoxy-hex-5-enoses formed on treatment with zinc dust have been characterized by conversion into the corresponding 1,2-dideoxy-hex-I-enitol acetates. During preparations of 6-deoxy-6-iodo-a-D-galactopyranosides from the corresponding 6-sulfonate esters, solvolytic side reactions have been observed which may include the formation of 3,6-anhydro-a-D-galactopyranosides with intramolecular participation of 3-0-methyl or 3-0-glycosyl substituents and subsequent loss of such substituents.GERALD OLIVER ASPINALL, DELPHI CHATTERJEE et LEV KHONDO. Can. J. Chem. 62, 2728(1984. On a examine la possibilitC d'utiliser la rkaction de Bernet-Vasella, qui permet de transformer des dCsoxy-6 halogCno-6 hexopyrannosides en hexkne-5 oses par action de la poudre de zinc, comme base d'une nouvelle mCthode pour cliver d'une faqon selective les liaisons glycosidiques d'oligo-et de polysaccharides complexes. Dans ['ensemble, la sCrie de rtactions implique: (a) qu'il faut gCnCrer des groupes hydroxyles primaires dans des oligo-et des polysaccharides qui sont par ailleurs complktement mCthylCs; (b) la formation de dCsoxy-6 iodo-6 hexopyrannosides grice a un dkplacement de sulfonates rtactifs par de I'iode et (c) un traitement par de la poudre de zinc qui est suivi par la formation de dCrivCs appropriCs des hexkne-5 oses libkres. On a pu transformer les oligosaccharides portant des substituants P-D-xylopyrannosyles en positions 2-0-(4), 3-0-(17), 4-0-(12) et 3-0-ainsi que 4-0-(8) en dCrivCs qui sont par ailleurs complktement mCthylks, qui contiennent chacun des rksidus dCsoxy-6 iodo-6 a-D-galactopyrannosides de mCthyle et qui peuvent servir de substrats modkles pour diffkrents environnements structuraux. Dans chaque cas, on a caractkrisC les didksoxy-5,6 hexkne-5 oses qui se forment par traitement avec de la poudre de zinc en les transformant en acetates des didksoxy-1,2 hexkne-l itols correspondants. Lors de la prkparation des dksoxy-6 iodo-6 a-D-galactopyrannosides a partir des sulfonates-6 corresp...
Can. J. Chem. 65,2069 (1987. Reduction of uronic acid residues in permethylated polysaccharides from Sterculin urens and S. caudara gums, followed by transformation of the resulting hexose into 6-deoxy-6-iodohexose residues, affords modified polysaccharides that undergo depolymerization on treatment with zinc dust. The main products after reduction with sodium borohydride are hexenitolterminated oligosaccharides. Their structures have been assigned as members of a series of 0-[a-L-rhamnopyranosyll-(1 +3)-1,2-dideoxyhex-I-enitol derivatives, with and without attendant P-D-galactopyranosyl substituents, on the basis of nuclear magnetic resonance and mass spectral data and compositional analysis of trideuteriomethylated derivatives. The structures of the polysaccharides have been reassessed in the light of these and other experiments, and may now be formulated as containing a backbone of alternating 4-linked a-D-galacturonic acid and 2-linked a-L-rhamnopyranose residues bearing a minimum of three types of side chains attached at specific sites. Characterization of some of the degradation products provides evidence that limited degradation had occurred during methylation of the glycuronans.GERALD OLIVER ASPINALL, LEV KHONDO et BRUCE ALAN WILLIAMS. Can. J. Chem. 65,2069Chem. 65, (1987. La reduction de rtsidus d'acide uronique de polysaccharides permtthylts provenant de gommes de Sterculia urerls et de S. caudata, suivie d'une transformation de l'hexose qui en rtsulte en rtsidus dtoxy-6 iodo-6 hexose, fournit des polysaccharides modifits qui subissent une dtpolymerisation lorsqu'on les traite par de la poudre de zinc. Les produits principaux provenant d'une rtduction par le borohydrure de sodium sont des oligosaccharides se terminant par un hexknitol. En se basant sur des donnees de rtsonance magnttique nucltaire et de spectre d e masse ainsi que sur des analyses de composition des dtrivts trideuttromtthylts, on a attribut leurs structures aux membres d'une strie de dtrivts 0-[a-L-rhamnopyrannosyll-(1-3)-didtoxy-1,2 hexene-1 itols qui pouvaient aussi porter des groupements P-D-galactopyrannosyles. On a rttvalut les structures des polysaccharides a la lumiere de ces experiences ainsi que d'autres et on peut maintenant affirmer qu'elles contiennent une unite de base formte d'acide a-D-galacturonique lit par la position 4 qui alterne avec un rtsidu du a-L-rhamnopyrannose lit par la position 2; cette unite repetitive porte un minimum de trois types de chaines lattrales qui sont attachtes ides sites sptcifiques. La caractirisation de quelques produits de dtgradation fournit des donntes permettant d'affirmer qu'il s'est produit une degradation limitee au cours de la mtthylation des glycuronanes.[Traduit par la revue]Exudate gums from the Sterculia genus contain structurally similar, partially acetylated polysaccharides with residues of D-glucuronic acid, D-galacturonic acid, D-galactose, and L-rhamnose (1-5). The most detailed studies have been carried out on S . urens gum and led to the formulation of two structural regi...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.