Talopyranose synthesis

Z. GanandF. Kong, Synthesis of 2,6-dioxabicyclo[3.3.1]heptanes l,3-anhydro-2,4,6-tri-0-benzyl-jS-D-talopyranose, Carbohydr. Lett., 1 (1994) 27-30. 

A. K. Chatterjee, D. Horton, J. S. Jewell, and K. D. Philips, Synthesis of 1,6-anhydro derivatives of 2-amino-2-deoxy-jS-D-talopyranose and 4-amino-4-dcoxy-/i-n-talopyranose, Carbohydr. Res., 7 (1968) 173-179. 

The aldolization mentioned was subsequently used461 for an interesting synthesis of branched-chain sugars. Thus, on reaction with formaldehyde, 78 gives, stereospecifically, 1,6-anhydro-3-C-(hydro xy-methyl)-2,3-0-isopropylidene-/3-D-(yxo-hexopyranos-4-ulose, which subsequently undergoes reduction at C-4 by a crossed Cannizzaro reaction leading to l,6-anhydro-3-C-(hydroxymethyl)-2,3-0-isopropyl-idene-/3-D-talopyranose. On the other hand, an attempt to condense 78 with ethyl formate did not result in the expected 3-C-formyl derivative only the dimer 88 was obtained.461... 

D. Horton and J. S. Jewell, Synthesis of l,6-anhydro- 3-D-talopyranose from derivatives of D-galactose and D-mannose, Carbohydr. Res., 5 (1967) 149-160 G. J. F. Chittenden, Oxidation of some derivatives of D-galactose with methyl sulphoxide-acid anhydride mixtures a route to derivatives of D-glucose and D-talose, ibid., 15 (1970) 101-109. 

Oxirans. - The synthesis of l,2-anhydro-3,4-di-0-benzyl-6-deoxy-a-D-glucopyranose and its conformational analysis have been reported. A range of epoxides have been prepared by base treatment of bromohydrins, which were made by reaction of hydrogen bromide with aldonolactones. A one-pot conversion of vicinal diols into epoxides employs halohydrin ester intermediates generated from cyclic orthoacetates and either acetyl bromide or trimethylsilyl chloride. Levoglucosenone has been transformed into l,6 3,4-dianhydro-p-D-talopyranose by way of a trn/w-iodo-acetoxylation of the alkene moiety... 

The preparation of some glycosylated ribitols as useful building blocks for the synthesis of certain teichoic acids has been described. The 1,6-anhydro-P-D-talopyranose (13), a key intermediate, is readily accessible from l,6-anhydro-23-< -(S)-benzylidene-p-D-mannopyranose. Thus coupling of (13) with S-ethyl-2,3,4-tri-0-acetyl-l-thio-a-L-rhamnopyranoside affords the L-ribitol derivative (14) after further IM Ocessing. Also the 4-0-allyl derivative (IS) is a suitable precursor of glycoside (16). 

Other Anhydrides. - Stereoselective chemical and chemoenzymatic approaches to the preparation of 1,6-anhydrohexopyranoses have been reviewed, and base treatment of pentabromophenyl glycosides has been investigated as an improved procedure for the synthesis of 1,6-anhydro sugars. Treatment of O-benzylated-3-O-acetyl-glycosyl chlorides with base (KO Bu, THF) has allowed syntheses of l,3-anhydro-2,4,6-tri-0-benzyl-P-D-talopyranose, l,3-anhydro-2,4-di-C -benzyl-a-L-arabinopyranose and 1,3-anhydro-2,4-di-0-benzyl-6-deoxy-P-L-talopyranose. The theoretical solution conformation of methyl 3,6-anhydro-a-D-galactopyranoside has been studied using ab initio calculations. The computed conformation was similar to that adopted in the crystal (X-ray analysis). ... 

Bromination of unsaturated lactone 5 (Br2,CH2Cl2) gave only the dibromo compound 6, whereas unsaturated lactone 7 afforded 8 under the same conditions. 2-Acetamido-4-bromo-2,4-dideoxy-talopyranose derivatives have been prepared via 2-acetamido-l,6 3,4-dianhydro-2-deoxy-P-D-talopyranose. The synthesis of deoxyiminoalditols from brominated aldonolactones is covered in Chapter 18. 

The synthesis of l,2-anhydio-3,4,6-tri-0-benzyl-P-D-talopyranose has been published,as have syntheses of l,2-anhydro-3,4-di-0-benzyl-p-L- and P-D-rhamnopyranose. Some 2-(9-Ts free sugar derivatives on treatment with base have afforded the 1,2-anhydro compounds 8-10. Conditions have been found for the conversion of tri-O-methyl-D-glucal into predominantly eith the... 

Conformational analyses by n.m.r. and computational methods have been reported for the following compounds l,2-anhydro-3,4,6-tri-0-benzyl-P-D-talopyranose, anhydro sugars 13 and similar hexopyranose derivatives, methyl 3,4-0-isopropylidene-a- and P-D-galactopyranoside and their di-O-acetates and di-O-methyl ethers, 3,4-0-(/ )-benzylidene-D-ribono-1,5-lactone (see Chapter 6), and 6-deoxy-6-phosphonoyl-D-fructopyranoses (see Chapter 17 for synthesis). D-Glucospyranosylamine, its tetra-O-acetate and 4,6-0-benzylidene acetal and several N-acylated derivatives, together with D-[l- C]glucopyranosylamine, have been used in a conformational study by n.m.r. spectroscopy aimed at probing the existence of the reverse anomeric effect. ... 

---