E versus Z geometry in β-d-arabino-hexopyranosidulose oximes |
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Authors: | Matthias Lergenmüller Ulrich Klres Frieder W Lichtenthaler |
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Institution: | aClemes-Schöpf-Institut für Organische Chemie und Biochemie, Technische Universität Darmstadt, Petersenstraße 22, D-64287 Darmstadt, Germany |
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Abstract: | Koenigs–Knorr-type glycosidations of peracylated 2Z-benzoyloxyimino-glycopyranosyl bromides invariably proceed with retention of the Z-geometry. Accordingly, the many β-d-hexosidulose oximes in literature which were prepared in this way and for which the oxime geometry has not been addressed explicitly, are the Z-oximes throughout. By contrast, oximation of β-d-hexopyranosid-2-uloses leads to mixtures of E and Z oximes readily separable and structurally verifiable by 1H and 13C NMR. Configurational assignments rested on comparative evaluation of NMR data of E and Z isomers, and, most notably on an X-ray structural analysis of the pivaloylated isopropyl 2E-benzoyloxyimino-2-deoxy-β-d-arabino-hexopyranoside revealing the unusual 1S5 1,4B conformation for the pyranoid ring. |
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Keywords: | Hexosidulose oximes E versus Z geometry 1S5color:black" href="/science?_ob=MathURL&_method=retrieve&_udi=B6TFF-4X087HV-2&_mathId=mml4&_user=10&_cdi=5225&_rdoc=5&_acct=C000054348&_version=1&_userid=3837164&md5=3b634c82b2379c0c7ef24151e777aecf" title="Click to view the MathML source" alt="Click to view the MathML source"> sciencedirect com/scidirimg/entities/21cc 1" target="_blank">gif" alt="right harpoon over left" title="right harpoon over left" border="0">1 4B conformation |
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