Octoses synthesis

An interesting variation of the cyanohydrin synthesis is based on the application of the Strecker reaction 118], or an appropriate modification of it, to protected dialdo sugars to give glycosyl a-aminonitriles, with good levels of diastereoselectivity (ds > 90%) [19]. This approach was employed for a formal synthesis of the amino octose lincosamine from... 

See also J. S. Brimacombe, R. Hanna, A. K. M. S. Kabir, F. Bennett, and I. D. Taylor, Higher-carbon sugars. Part 1. The synthesis of some octose sugars via the osmylation of unsaturated precursors, J. Chem. Soc. Perkin Trans. 1, p. 815 (1986). 

The Synthesis of N-Acetyl-lincosamine (6-Acetamido-6,8-dideoxy-D-ert/fhro-D-ga-lacto-octose), a Derivative of the Free Carbohydrate Moiety in Lincomycin, G. B. Howarth, W. A. Szarek, and J. K. N. Jones, Chem. Commun., (1969) 1339-1340. 

The full configurations of the other synthetic octoses, nonoses and Philippe s decose remained unknown because these aldoses led to no meso alcohols and none of their alcohols was obtained from two aldoses. If both epimers from each cyanohydrin synthesis in the glucose, mannose and galactose series had been obtainable readily, most configurations in... 

H. Fritz, J. Lehmann, and P, Schlesselmann, Chain elongation by a seettringly stereospecific cyanohydrin synthesis The preparation and configurational assignment of 3,7-anhydro-D-threo-t-talo- and t-galacto-octose, Carbohydr. Res. 74 309 (1979). 

In summary, it can be said that, in homogeneous alkaline solution, either methanolic or aqueous, an equilibrium is established between the aldose, nitromethane, and deoxynitroalditols, and that, for successful addition, this equilibrium must be displaced in favor of the alditols, either through precipitation of their sodium salts from methanolic solution, or by direct crystallization from aqueous solution. Because of these requirements, the method is not so widely applicable as the cyanohydrin synthesis, but, for selected sugars, such as n-gZgcero-D-ZaZo-heptose and o-erythro-i -manno-octose, its simplicity and the satisfactory yields obtained make it the method of choice. 

The presented review describes total syntheses directed towards 6-amino-6,8-dideoxy-D-eryt/iro-D-galacto-octose, commonly named lincosamine - the sugar component of the antibiotic lincomycin. In the first part we present total syntheses of lincosamine that start from carbohydrate precursors. The D-galactose-derived aldehyde is the most frequently used synthon. In the second part, total syntheses of lincosamine from non-carbohydrate precursors are presented. This part of the review is divided into two subsections. The first one groups syntheses based on the application of furan compounds. In the second one we present a hetero-Diels-Alder approach to the synthesis of lincosamine. 

The synthesis of higher-carbon carbohydrates has been reviewed (in Japanese) there is particular reference to tunicamine (an undecose) and coverage of octoses, nonoses, and decoses. ... 

The synthesis of sugars by iterative, diastereoselective homologation of aldehydo-sugars with 2-trimethylsilylthiazole mentioned last year (see Vol. 19 p 5 ref. 11) has been extended up to nonose derivatives. The newly created chiral centre at C-2 invariably bore an erythro relationship to the C-3 substituent thus, D-glyceraldehyde led to the D-allose derivative (19)f and the meso-octitol (20) was obtained via the corresponding octose. 

Acyclic Alditols. - Brimacombe s group have published full details of their work on the stereoselective synthesis of higher sugars, some of which is covered in Chapter 2 other papers describe the Sharpless oxidation of the octose derivative (1) to give the oxiran (2), and hence the D-erythro isomer (3), osmylation... 

The terminal steps for converting the resulting Cg unit to MTL were not determined in the study of Brahme et al. (40). They postulate that an isomerization of the octulose to an octose occurs, followed by dephosphorylation and reduction at the C8 car-bon- Then, a transamination of the precursor 6-ketooctose occurs and is followed by a thiomcthylation of Cl to complete the synthesis of MTL. 

A review lecture including the synthesis of branched-chain sugars using the dithiane route and glycoside synthesis with branched-chain sugars has been published and full reports on the synthesis of the y-octose obtained from isoquinocycline A and of related 4-C-hydroxyethylhexose derivatives have now appeared (see Vol. 10, p. 98). 

In addition to L-glucose and L-mannose, other sugars that have been prepared conveniently by the nitromethane synthesis include L-gulose (150), the aldoheptoses from D-mannose (151), and D-erythro-h-manno-octose (152),... 

A synthesis of the octose moiety of ezomycin A from D-galactal 93... 

A full paper on the synthesis of octoses by the "naked sugar" approach has been published (see Vol.23, Chapter 2, ref.31). An improved, shorter version of this synthesis employs a Wittig Homer reaction instead of the original Mukayama cross-aldolization for chain-extension. Similar work has been reported by a Japanese group. ... 

Paulsen s group has reported the synthesis of derivatives (256) and (257) of the hydroxyethyl-branched octose that is found as a component of the quinocycline complexes isolated from Streptomyces aureofaciens. The route from the epoxyketone (255) is outlined in Scheme 59. An identical route was used to prepare branched-chain analogues in the o-series, in which it was shown that acid-catalysed methanolysis of the hydroxyethyl-branched derivative (258) yielded the more stable isomer (259) via the anhydro-sugar d-(257). Paulsen s group has also described a synthesis of a derivative (260) of pillarose (see Vol. 9, p. 99), a component of the antibiotic pillaromycin, using the dianion (261) prepared from 2-hydroxymethyl-l,3-dithiane to introduce the branch at C-4 (Scheme 60). A similar approach, using the anion derived from 2-methyl-l,3-dithiane, and subsequent desulphurization and reduction, etc., was adopted in a synthesis of a derivative (262) of aldgarose (4,6-dideoxy-3-C-[(i )-l-hydroxyethyl]-D-W6o-hexopyranose 3,3 -cyclic carbonate) (cf. Vol. 8, p. 100). 

Burgess et al. developed a novel approach for the synthesis of polyhydroxylated compounds such as castanospermine 87 and swainsonine 89 ° utilizing alkoxyallylboration of as one of the key steps (Eigure 25.12). Similarly, Jadhav and Woerner were able to convert the octose derivative 90 into the polyhydroxyindolizidine 91 in seven further transformations (Figure 25.12). Several of these indolizidines exhibit potent anti-cancer, anti-viral, and anti-AIDS activities. 

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