Branched-chain sugars cyclitols

Syntheses of amino-derivatives of branched-chain sugars, cyclitols and nucleosides are covered in Chapters 14, 18 and 20, respectively. 

Principal Branched-chain Sugars and Cyclitols of Natural Occurrence... 

M. Funabashi and J. Yoshimura, Branched chain sugars. Part 14. Synthesis of new branched-chain cyclitols having myo- or scyllo-, and muco-configuration from 3-< -benzyl-5,6-dideoxy-5-C-(l,3-dithian 2-yl)-6-nitro-L-idofuranose and D-glucofuranose, J. Chem. Soc. Perkin Trans, p. 1425 (1979). 

The terms aminoglycoside as well as aminocyclitol antibiotic which are used for this class of natural products refer to the structural aspect. Most of the aminoglycoside antibiotics contain aminosugars and an aminocyclitol or a cyclitol moiety. The middle furanose part in streptomycin is called streptose and was the first branched-chain sugar obtained from microorganisms. The other rings in streptomycin are a IV-methyl-L-glucosamine moiety and an aminocyclitol called streptidine (O Fig. 20). 

During the past nine years the subject of total synthesis of sugars and cyclitols has been vividly developed. The discovery of a large number of unusual sugars in nature—deoxy, amino, branched chain sugars (many of them components of antibiotics)—made their synthesis attractive. On the other hand, improvements in organic reagents and synthetic methods allowed a return to older preparations which could be now better performed. Finally, some synthetic ideas already described in this series, in the first chapter of the volume on the total synthesis of carbohydrates, are further expanded. 

A number of branched chain nitro-cyclitols have been prepared by Michael addition of lithium dithiane to unsaturated nitrosugars followed by cyclization (Scheme 4) conformational effects in the 6-nitro-a/de/iydo-sugar on the stereo-... 

The good yields obtained in the cyclization of appropriate radical precursors show that this is a convenient method for the synthesis of branched-chain cyclitols from carbohydrates. In addition, an interesting stereoelectronic effect in the cyclization of these acychc sugar derivatives is demonstrated the stabilizing effect of electron-attracting groups vicinal to carbon-centered radicals determines the preferred conformation in the transition state and the stereochemical outcome of the reaction. 

All three components are unusual the amino sugar is based on L-glucose streptose is a branched-chain monosaccharide and streptidine is not a sugar at all, but a cyclohexane derivative called an amino cyclitol. 

Anhydromaltose has been converted to the pseudo-disaccharides (25) containing 3-amino-3-deoxy-epz-inositol or 1-amino-l-deoxy-l-L-myo-inositol via the 6-deoxy-6-nitromaltose derivative (26). The branched-chain unsaturated 6-nitro-sugar (27), prepared conventionally from D-glucose, yielded isomeric dithianyl adducts which were similarly cyclized to give the nitro-cyclitols (28) and (29), of interest as potential intermediates for the synthesis of tetrodo-... 

Sugars Unusual sugars (amino, deoxy and methyl sugars, and sugars with branched chains). Reduction products (sugar alcohols, cyclitols, streptidine). Oxidation products (uronic acids, aldonic acids, sugar dicarboxylic acids). 

A detailed study on the radical cyclization of various protected sugars 80 (R= alkyl, silyl or acetals, X=° Br or I), on treatment with tributytin hydride and AIBN to produce branched-chain cyclitols 81, has been disclosed. ... 

These developments are here surveyed within the same guidelines as were used previously that is, discrete compounds will be dealt with which have one carbon-carbon multiple bond within the main sugar-chain. As before, enols, enediols, enones, dienes, and dienones will not be considered, nor will unsaturated cyclitols or heterocyclic compounds composed partially of acyclic carbohydrates. The first derivatives having carbon substituents attached by a double bond at a branch-point have now been prepared by application of the Wittig reaction to suitably protected glycosulose compounds these compounds are also arbitrarily excluded, as are ethers or acetals bearing unsaturated substituents. 

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