Hexopyranose spectroscopy

SDMA in toluene for 20 min at 0° under an argon atmosphere gave the 5-C-(phenylphosphinyl) compound 124, which, on acid hydrolysis, afforded the 5-C-(phosphinyl)hexopyranose 125. This was treated with acetic anhydride-pyridine, to give the peracetates (126), from which crystalline l,2,4-tri-0-acetyl-3,6-di-0-benzyl-5-deoxy-5-C-[(S)-phenyl-phosphinyl]-/ -D-glucopyranose-4C1 (127) was isolated in 2% overall yield from 123 none of the other diastereoisomers of 127 were obtained. Structure 127 was established by 400-MHz, -n.m.r. spectroscopy (see Section 11,5). 

The Raman and infrared spectra of methyl 3,6-dideoxy-/3-D-nbo-hexopyranoside were recorded130 at room temperature and lower temperatures. Correlation between the O O distances and four bands identified at 3530, 3470, 3442, and 3216 cm-1 was made. I.r. spectroscopy has been applied131 to the study of inter- and intra-molecular hydrogenbonding in hexopyranoses and their derivatives. The calculated OH O distances were correlated with frequency shifts measured in the p(OH) region. 

Most aldohexopyranoses exist in a chair form in which the hydroxymethyl group at C(5) assumes an equatorial position. All the P-D-hexopyranoses exist predominantly in the 4Ci form since the alternative C4 conformer involves a large unfavourable xyn-diaxial interaction between the hydroxymethyl and anomeric group (Figure 1.8). Most of the a-D-hexopyranosides also adopt the 4Ci conformation preferentially. Only ot-idopyranoside and a-D-altropyranose show a tendency to exist in the C4 conformation, and they coexist with the alternative 4Ci conformations according to H-NMR (hydrogen nuclear magnetic resonance) spectroscopy studies. 

Recently, all eight diastereoisomeric 1,6-anhydro-P-D-hexopyranoses and three related model compounds have been studied in O-depleted water using 1 0 NMR spectroscopy methodology [94,97]. Chemical shift assignments for all resonances in the eleven compounds were made. The results for glucosan ( 95), mannosan( 96), and galactosan ( 97) as well as the three model compounds 98-100 are shown below. 

Conformational analyses by n.m.r. and computational methods have been reported for the following compounds l,2-anhydro-3,4,6-tri-0-benzyl-P-D-talopyranose, anhydro sugars 13 and similar hexopyranose derivatives, methyl 3,4-0-isopropylidene-a- and P-D-galactopyranoside and their di-O-acetates and di-O-methyl ethers, 3,4-0-(/ )-benzylidene-D-ribono-1,5-lactone (see Chapter 6), and 6-deoxy-6-phosphonoyl-D-fructopyranoses (see Chapter 17 for synthesis). D-Glucospyranosylamine, its tetra-O-acetate and 4,6-0-benzylidene acetal and several N-acylated derivatives, together with D-[l- C]glucopyranosylamine, have been used in a conformational study by n.m.r. spectroscopy aimed at probing the existence of the reverse anomeric effect. ... 

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