Branched aminosugars

Branched-Chain Aminosugars and Aminocyclanols via Dialdehyde-Nitfoalkane Cyclization... 

This review presents an evaluation of the experimental material available to illustrate the scope and limitations of the dialdehyde-nitro-alkane cyclization and its preparative utility as a synthetic entry to branched chain aminocyclanols and aminosugars. 

Application of the reaction sequence periodate oxidation - cyclization with nitromethane hydrogenation to rt6o-nucleosides provides a general synthetic entry to 3-aminohexosyl p5nimidines i7-20) and purines 21-as) which otherwise are not readily accessible. That this sequence can be extended to nitroethane to give 3 -C-methyl branched aminosugar nucleosides, has been demonstrated, starting from uridine 4.10,26)... 

Table. Chemical shifts in CDCI3 of substituent resonances in fully acetylated C-methyl branched aminocyclanols and aminosugars...

Naturally occurring polysaccharides can occur either as individual carbohydrate molecules or in combination with other naturally occurring substances, such as proteins (glycoproteins) and lipids (glycolipids). In all cases the polysaccharide section may have linear or branched chain structures, which often contain the derivatives of both monosaccharides and aminosugars (Figure 1.20). 

In this way various protected carbohydrates and aminosugars are obtained. There is a matching correspondence between a-branched (5) or (/ )-configurated aldehydes and (S) or (/ )-pro-Une, respectively. Thus, the reaction of 25 with the (R)-configurated 2,3-di-O-isopropylidene-D-glyceraldehyde gives the double acetonide of D-psicose in 76% yield. Acidic deprotection with Dowex gives the parent D-psicose. A similar route has been reported by Cordova and co-workers [144]. 

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). 

A soln. of methyl 2-C-(aminomethyl)-4,6-0-benzylidene-2,3-dideoxy-2-[(/ -tolyl-sulfonyl)amino]-a-D-ribohexopyranoside in 90% acetic acid treated dropwise with aq. NaN02, and after stirring for 1 h the mixture poured into satd. NaHC03 spiro[methyl 4,6-0-benzylidene-2,3-dideoxy-a-D-ribo-hexopyranoside-2,2 -N-(/ -tolyl-sulfonyl)aziridine]. Y 89%. The products are valuable intermediates in the preparation of branched-chain aminosugars. F.e. and prepn. of the startg. m. s. R.J. Alves et al., J. Org. Chem. 53, 4616-8 (1988). 

Recently, Sherburn and coworkers reported interesting results on the HDA cycloaddition of parent [3]-[8]dendralenes with nitroso dienophiles and its application to a synthesis of branched aminosugars [32]. Scheme 2.21 depicts selected results of the full sequential DTHDA cycloadditions of parent [3]dendra-lene, 127 and [4]dendralene, 125, with nitroso dienophiles. [4]Dendralene 125... 

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