Ergebnisse und Probleme der O‐Glykosidsynthese

Abstract

Die Synthese von biologisch wichtigen Naturstoffen mit mehr oder minder kompliziertem Kohlenhydratanteil wirft erhebliche Probleme auf. Im vorliegenden Fortschrittsbericht wird über neuere Entwicklungen bei der Knüpfung der O‐Glykosidbindung — ausgehend von 1‐Halogenzuckern und von 1,2‐Zuckerorthoestern — berichtet. Dabei wird versucht, aufgrund reaktions‐mechanistischer Überlegungen vor allem den stereochemischen Ablauf von Glykosylierungsreaktionen besser zu verstehen. Die Untersuchung der Silbersalzabhängigkeit der Koenigs‐Knorr‐Synthese führte zu präparativen Verbesserungen des Verfahrens und zu neuen Vorstellungen über den Reaktionsablauf. Eine wesentliche Bereicherung der präparativen Möglichkeiten zur Synthese von trans‐Glykosiden war die Einführung von 1,2‐Zuckerorthoestern als Glykosylierungskomponente. Sehr bemerkenswerte Fortschritte sind vor allem auch bei der Synthese von cis‐Glykosiden, u. a. durch Ausnutzung von neuartigen Nachbargruppeneffekten, zu verzeichnen.

Stereoselective Syntheses of α-D-Ribopyranosyl Disaccharides [1]

“…In order to test the usefulness of 1 for preparing a-D-ribopyranosyl disaccharides, 1,2:3,4-di-Oisopropylidene-a-D-galactopyranose and 1,2:5,6-di-O-isopropylidene-a-D-glucofuranose were cho sen as representative hydroxy com ponents [5]. Prior to glycosylations with 1, these O-iso-* Reprint requests to Dr. W. V. Dahlhoff.…”

Synthesis and characterization of functional six-membered ring carbonates for the preparation of orthogonal couplers

“…Starting from 2-N-acetylamino-2-deoxy--D-glucopyranose halogenation was done according to Horton [45] (yield 65-72 %). Then in a König Knorr glycosidation [46][47][48][49][50] the acetylated sugar was reacted with 2-azidoethanol [51] (yield 63.6 %). The selective deacetylation was performed according to Zemplén [52] in methanol at 0 °C using sodium methoxide (30 mol%).…”

Koenigs–Knorr Syntheses of some α-1 → 2 and β-1 → 2 linked Nitro Disaccharides

“…The methods used included an application of the nitromethane cyclization t o a given disaccharide (I), the nucleophilic addition of partially blocked n~onosaccharides to nitroolefinic sugar derivatives (2), and KoenigsKnorr type condensations (3). The last-mentioned reactions were performed with per-0-acetylglycosyl bromides both under classical conditions (4-6) and by applying the Bredereck method (5-7) of trityl ether displacement, and moderate yields (14-25%) of P-1 -t 6 linked nitro disaccharides were obtained.The present work was undertaken with a view t o exploring whether preparative advantages might be derived, in our special area of interest, from the Helferich modification (5,6,8,9) of the Koenigs-Knorr reaction, i.e., the condensation promoted by mercuric cyanide. We were concurrently engaged in studies (10) pating benzyl ether group a t C-2, hoping to make advances in the complex problem (4-6) of steric control in glycosylation, particularly as regards the synthesis of such 1,2-cis glycosides .…”

“…The present work was undertaken with a view t o exploring whether preparative advantages might be derived, in our special area of interest, from the Helferich modification (5,6,8,9) of the Koenigs-Knorr reaction, i.e., the condensation promoted by mercuric cyanide. We were concurrently engaged in studies (10) pating benzyl ether group a t C-2, hoping to make advances in the complex problem (4-6) of steric control in glycosylation, particularly as regards the synthesis of such 1,2-cis glycosides .…”

“…The methods used included an application of the nitromethane cyclization t o a given disaccharide (I), the nucleophilic addition of partially blocked n~onosaccharides to nitroolefinic sugar derivatives (2), and KoenigsKnorr type condensations (3). The last-mentioned reactions were performed with per-0-acetylglycosyl bromides both under classical conditions (4)(5)(6) and by applying the Bredereck method (5-7) of trityl ether displacement, and moderate yields (14-25%) of P-1 -t 6 linked nitro disaccharides were obtained.…”