Aldoses 2- deoxy

In as far as other analytical methods are concerned, many specific reactions have been elaborated for the quantitative determination of 2-deoxy aldoses. 2-Deoxy-D-ribose (2-deoxy-D-erythro-pentose), a compound which was recognized early as playing an important role in biological systems, has been of particular interest. Overend and Stacey (43) have given a critical review of the methods available until 1952 for the estimation of 2-deoxy pentoses. A recent summary of specific methods for the identification and quantitative estimation of the different classes of deoxy sugars has been prepared by Dische (13). 

In connection with the Webb and Levy test, it should be mentioned that this test can also be applied to the estimation of all 2-deoxy aldoses, including those containing a terminal deoxy group, provided they have at least five carbon atoms in a straight chain 2-deoxy tetroses do not react (62). It has also been used for the estimation of 3-deoxy and 3, 6-di-deoxy hexoses, after their conversion to the corresponding 2-deoxy pentoses by removal of carbon 1 with periodate (24,25). 

Note 1. This convention is not needed for parent aldoses, only for deoxy aldoses, ketoses and similar compounds (see 2-Carb-10.4 and 2-Carb-11.2). 

Amino-2-deoxy aldoses. The behaviour of O-unprotected sugars is exemplified in D-gluco series after basic hydrolysis of the starting 2-benzamidoglycoside followed by buffering the medium with carbon dioxide and treatment with thiophosgene, an intermediate isothiocyanate was obtained.320 However, NMR revealed a temperature-dependent equilibrium of this isothiocyanate with a trans-fused OZT (Scheme 5). 

Amino-5-deoxy aldoses. Similarly to the precedent approach, a regio-selective access to C-5 anchored OZTs was developed from 5-amino-5-deoxy-1,2-<9-isopropylidene-a-D-gluco- and a-L-idofuranose through condensation with carbon disulfide (Scheme 13) 22,23... 

The Knovenagel condensation under basic conditions was first investigated with D-glucosamine chlorhydrate (28.HC1) as the sugar. The condensation of this reducing amino sugar with pentane-2,4-dione 1 in aqueous acetone in the presence of sodium carbonate afforded the pyrrole derivative 29 in 85% yield [99] (Scheme 5). The reaction was extended to other 2-amino-2-deoxy-aldose and carbon nucleophiles [100-104]. 

An account of the methods of synthesis of amino sugars has been given in an earlier Volume of this Series1 attention is devoted in this Section to methods recently developed. Several general methods have been employed for the synthesis of 2-amino-2-deoxy-aldoses these respectively involve direct amination of suitable sugar derivatives, interconversion of sugar series, and ascent or descent of a series with or without concomitant amination or molecular rearrangements. 

An N-alkyl group is not removed under the reaction conditions, and an iV-substituted 2-amino-2-deoxy-aldose is formed. Under the same reaction conditions, anA-benzyl group is cleaved (with the uptake of a further mole of hydrogen per mole), to give the free 2-amino-2-deoxy-aldose and toluene ... 

A further example has been given of the synthesis of a 2-deoxy-aldose by the addition of water to a glycal, but, as this reaction is known to be accompanied by competing eliminations,1 it is being replaced in synthetic work by more-specific addition procedures, for example, methoxymercuration (see p. 210). From the 4-deoxy derivative of D-glucal, prepared by standard procedures from 2,3,6-tri-O-acetyl-4-deoxy-D-xy/o-hexopyranosyl bromide, 2,4-dideoxy-D-threo-hexose was obtained.35... 

Finally, further examples of unsaturated 1-nitroalditols have been described, and have been utilized in standard syntheses of 2-deoxy-aldoses by this means, 2-deoxy-D-rtho-hexose,174 2-deoxy-D-manno-heptose,175 2-deoxy-D-gaiacto-heptose,176 and 2,6-dideoxy-L-manno-heptose177 have been prepared. The reaction of ammonia with 3,4,5,6-tetra-0-acetyl-l,2-dideoxy-l-nitro-L-arabino-hex-l-enitol has been further examined, and found to proceed stereospecifically to give... 

Reduction of 1-nitro-l-alkene derivatives such as 65 provided 2-deoxy-aldose oximes and their elimination products such as 66 and 67, respectively (Scheme 11). The oxime 66 could be converted into the corresponding free 2-deoxy-sugar, 2-deoxy-aldononitrile and 2-deoxy-aldonic acid. Radical cyclization of 5-keto-aldose aldoximes to give aminocyclopentitol derivatives is covered in Chapter 18. 

Scheme 55. Partial fragmentation of a 3-acetamido-3-deoxy aldose diethyl dithioacetal showing fragment A.

A variety of racemic deoxy-aldoses and -ketoses, including oleose, dlgltoxose, 2-deoxygalactose, 3-deoxyfructose, and 1,3-dideoxyfructose, have been synthesized from dienes (43) (Scheme 11). 

The glycals, first reported by Fischer and Zach, were extensively investigated by Bergmann and Schotte. They are important intermediates for the interconversion of epimeric sugars and for the preparation of 2-deoxy-aldoses (Chapter II). 

---