Reactions and Other Features

Deamination of 2-amino-l,5-anhydro-2-deoxy-D-mannitol with nitrous acid gave principally l,5-anhydro-2-deoxy-D-e/ yt/fru-hex-3-ulose (68%), by migration of H-3, and some 2-deoxy-D-a/ a6/no-hexose (8%) and 1,5-anhydro-D-glucitol (6%). It was established that 2-deoxy-D-nrai //in-hexose is formed via a hydride-shift mechanism, rather than by acid-catalysed hydration of D-glucal produced by an elimination pathway. 

Reinvestigation of the reaction of 2-amino-2-deoxy-D-gIuconic acid with hot acetic anhydride has shown that the principal products are the )- and (Z)-furanone derivatives (137) and the pyranone (138). The crystalline 

Machinami, K. Kobayashi, Y. Hayakawa, and T. Suami, Bull. Chem. Soc. Japan, 1975, 48, 3761. 

The A -acylation of 2-amino-2-deoxy-D-glucose with acetic anhydride in aqueous solvent systems has been carefully examined as a model system for the selective A -acylation of chitosan with carboxylic anhydrides. The selective iV-acylation of amino-sugar components of the gentamicin antibiotics is mentioned in Chapter 20. 

Another key step in this synthesis, which was aimed at a hexose analogue of prumycin (see p. 62), necessitated the reduction of the azido-group of benzyl 4-azido-3-0-benzyl-2-(benzyloxycarbonyl)amino-2,4-dideoxy-a-D-galactopyrano-side without removal of the other protecting groups. This selective reduction was accomplished by careful catalytic hydrogenation over Raney nickel (added in small portions) at room temperature. 

On heating, with benzaldehyde, methyl P-L-arabinopyranoside gave, after ben-zoylation, the 3,4-0-(S)-benzylidene derivative (93), whereas selective hydrolysis of a 1 1-mixture of the diastereoisomers gave the (R)-isomer 9A)V The pure isomers (93) and (94) were converted into methyl 3,4-0-(S)- and -(R)-benzylidene-p-L-ribopyranoside, respectively, on successivedebenzoylation, oxidation (DMSO-acetic anhydride), and reduction (sodium borohydride). Under anhydrous acid conditions, methyl 3,4-0-(R)-benzylidene-P-D-ribopyranoside rearranged to the 

3-0-(J )-benzylidene derivative, which gave a pseudoequilibrium mixture containing the four pyranosidic acetals on further rearrangement. At higher concentrations of acid, ring-contraction also occurred to give the diastereoisomers (95) as the only products. Similar results were obtained with methyl 3,4-0-(S)-benzylidene-P-D-ribopyranoside. 

Treatment of methyl 2-0-benzoyl-3,4-0-benzylidene-P-D-arabinopyranoside with triphenylmethylium tetrafluoroborate in acetonitrile gave an equilibrium mixture of the benzoxonium ions (96) and (97), which reacted with chloride or iodide ions to give(98) and (99) in the ratio of 6 1 (X = Cl) or 1 2 (X = I), signifying differences in the reactivities of (96) and (97) towards different halide ions. The 

Jacobsen, B. Nielsen, and C. Pedersen, Acta Chem. Scand., 1977, B31, 359. 

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