2.6- Dideoxy sugars synthesis

A presentation by Webber and co-workers dealing with the synthesis of fluorodeoxy sugars regrettably had to be left out of this monograph because of unexpected difficulties in the preparation of the manuscript. The fourth aspect was represented in the symposium by two presentations involving important aspects of deoxy and dideoxy sugars by Osborn and Heath respectively which unfortunately were not incorporated in this monograph. 

Several methyl ethers of the above dideoxy sugars have been synthesized,2 essentially by the above methods, with introduction of a methoxyl group (usually i t C-3) at a convenient stage of the synthesis. 

Recently, some knowledge was acquired concerning nature s approach to the synthesis of dideoxy sugars. 6-Deoxygenation of glucose seems to follow a redox pathway via the nucleotide glucoside dTDP-glucose with oxidoreductase which leads to a 6-deoxy-4-uloside [1],... 

Highly stereocontrolled synthesis of 2,6-dideoxy sugars and its use in the synthesis of macrolide antibiotics 92YGK303. 

Andreana et al. [25] have recently invoked RCM to prepare /J,y-unsaturated <5-lactones (Scheme 3). Exposure of dienes of general type 13 to either 2 or 4 (which could be used at lower loadings) readily furnished lactones 14. For other examples of a,/ -unsaturated <5- and y-lactone synthesis by RCM see Ref. [26]. Variation of the configuration at the chiral carbons and the ligand for the asymmetric dihydroxylation reaction allows access to an array of biologically important dideoxy-sugar derivatives. 

Umezawa, S, Tsuchiya, T, Okazaki, Y, Synthesis of 3,4-dideoxy-3-enosides and the corresponding 3, 4-dideoxy sugars. Bull. Chem. Soc. Jpn, 44, 3494 1977. 

Methyl 2Z,5-hexadienoate (126) undergoes cyclization to / S-parasorbic acid when treated with polyphosphoric acid. Torssell and his co-workers employed the substrate thus obtained for a new series of sugar synthesis. OL-Desosamine was synthesized in an essentially similar way to that described above. Analogously, DL-chalcose (127, 4,6-dideoxy-3-0-methyl-DL-xy/o-hexopyranose), was obtained, that is, by oxirane ring opening in racemic epoxy-lactone 122 with methanol in the presence of p-toluene-sulfonic acid. 

Tartrate esters also feature as the chiral reagents in the Sharpless asymmetric epoxidation, a reaction applied in the synthesis of deoxy-sugars. Two groups have epoxidized divinyl carbinol (33) and converted the resulting mono-epoxlde (3 ) into the 2,6-dideoxy-sugars D-ollvose (35), its 3- -niethyl ether (D-oleandrose) and 4-0 -benzyl ether, and Into D-digltoxose (36) and Its 4- -benzyl ethers (Scheme 7). Epoxidation of the meso-... 

Guided addition of the elements of ammonia to an allylic alcohol has been demonstrated in syntheses of 3-amlno-2,3-dideoxy-sugars. Thus, two groups employed the halocyclization of the 4- -trichloro-acetimido-derlvatlve (16) in the synthesis of methyl a-L-ristosaminide (17) (Scheme while a daunosamlne derivative. 

Under conditions of thermodynamic control the enantio-complementary nature of the FruA-RhuA biocatalyst pair enables construction of mirror image products 78 and ent-78 from racemic 3-hydroxybutanal 77 with similar selectivity, but preference for opposite enantiomers [25]. The all-equatorial substitution in the predominant product can facilitate its separation by crystallization so that the remaining mixture can be re-subjected to further equilibration to maximize the yield of the preferred isomer 78 [177]. This general technique has recently found an application in a novel approach for the de novo synthesis of 4,6-dideoxy sugars such as 4-deoxy-r-fucose 81 or its trifluoromethylated analog (Figure 5.37) [25]. 

Reissig and Pfrengle have developed an attractive strategy for the synthesis of 3-amino-2,6-dideoxy sugars. The required starting template 3,6-dihydro-2H-l,2-oxazine was conveniently produced by the addition of lithiated alkoxyallenes (prepared in situ) to o-glyceraldehyde-derived nitrone. ... 

Scheme 12 Pfrengle s synthesis of 3-amino-2,6-dideoxy sugars.

An attractive feature in this reaction is the possibility of direct substitution and formation of unblocked sugar derivatives containing one or more chlorodeoxy function in essentially two steps. Another facet is the formation of methyl 4,6-dichloro-4,6-dideoxy-hexosides from certain methyl glycosides in one step. Such compounds could be valuable intermediates in the synthesis of dideoxy and diamino sugars of biological importance. 

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