Talose preparation

It has also been reported that D-galactose can be isomerized with molybdic acid to a mixture containing D-talose and D-gulose, but the yields are low.34-35 A number of derivatives of gulono-1,4-lactone have been prepared that, by reduction, would provide selectively protected derivatives of gulose. These derivatives will be discussed in subsequent Sections of this article. 

In addition to these physical studies at the Bureau, Tipson was able to return to his synthetic interests, both alone and in collaboration with other staff members. He was especially pleased to prepare D-talose in crystalline form, an accomplishment that had eluded Emil Fischer. Pursuing his longstanding interest in the reaction of sulfonic esters with iodide and following an earlier observation that the tetratosyl ester of erythritol is converted into butadiene by the action of sodium iodide and zinc, he demonstrated (with A. Cohen) that nonterminal unsaturation may be conveniently introduced into alditol derivatives by reaction of contiguous secondary sulfonates with sodium iodide and zinc dust in boiling A.A-dimethylformamide. This Tipson-Cohen reaction subsequently proved of great utility in other hands for the conversion of more complex carbohydrate structures into vicinal dideoxy derivatives. 

Hodosi, G. Kovac, P., Manipulation of free carbohydrates via stannylene acetals. Preparation of beta-per-O-acyl derivatives of D-mannose, L-rhamnose, 6-0-trityl-D-talose, andD-lyxose. Carbohydr. Res. 1997,303, 239-243. 

D-Talitol has been prepared by the reduction of D-talonolactone or D-talose. Recently, an improved method of preparation, the hydrogenation of D-altrose in high yield, has been described. ... 

Problem 22.54 Prepare o-talose from its C epimer, D-galactose (Problem 22.22). See Fig. 22-18. 

J. Gelas and D. Horton, Kinetic acetonation of D-galactose, D-allose and D-talose with alkyl propenyl ethers as a preparative route to the 4,6- O-isoptopylidene aldohexopyranoaes, Carbohydr. Res. 77 103 (1979). 

Formation of the identical sugars of the D-series, 6-deoxymannose (rhamnose) and 6-deoxytalose, seems to proceed by a different pathway. According to Winkler and Markowitz (13), GDP-6-deoxy-D-mannose is first converted to GDP-6-deoxy-D-lyxo-4-hexulose. This 4-keto intermediate is the direct precursor for the unspecific enzymatic reduction leading to GDP-6-deoxy-D-mannose and GDP-6-deoxy-D-talose. For a pyridine-nucleotide requiring enzyme, the transformation seems to be unusual because of its lack of stereospecificity. However, closer examination and evaluation of properties of the different 4-keto-intermediate reductases must await availability of more highly purified enzyme preparations. 

Applying the same route, d- and L-mannose were obtained in a five-step synthesis (39% overall yield) from furfural. Similarly, the same methodology was extended to the preparation of d- and L-gulose and d- and L-talose (19% yield) [229]. 

J. Defaye, Desamination nitreuse de la D-galactosamine. Preparation des 2,5-anhydro-D-talose et 2,5-anhydro-D-talitol, Bull. Soc. Chim. Fr. p. 999 (1964). 

Preparation. D-Talose was first prepared by reduction of D-talono-1,4-lactone obtained by epimerization of D-galactonic acid.133 The sugar is also obtained by oxidation of D-galactal,134 or by configurational-inversion procedures from derivatives of D-mannose or D-galactose.135... 

Preparation. 6-Deoxy-L-talose was prepared by a method described by Collins and Overend.187 The yield has been improved by a method which involves inversion of configuration at C-4 of a derivative of methyl a-L-rhamnopyranoside.188 Other similar strategies have been described.189... 

The Danishefsky group has extensively applied this methodology to total synthesis of a number of natural products.45 In particular, the method has provided entry to several types of carbohydrate, both simple and complex. For example, the monosaccharide L-talose could be prepared in just a few steps using a hetero Diels-Alder reaction [Eq. (15)].44 ... 

Chemical Synthesis.—Purine nucleoside 5 -monophosphates enriched with or 0 on the phosphate group are conveniently prepared by treating phosphorus pentachloride in dry triethyl phosphate with one equivalent of the appropriately labelled water to give PO]- or P 0]P0Cl3, which is not isolated but mixed with adenosine or guanosine in the same solvent. Work-up of the resulting 5 -phos-phorodichloridate in similarly labelled water permits the formation of pO]-or P 0]AMP (or GMP) in fair yield with good enrichment. The 5 -monophos-phates of the 5 -C-methyl uridines derived from 6-deoxy-D-allose and 6-deoxy-L-talose have been prepared via phosphorylation of the 2, 3 -0,0-ethoxymethyl-idene derivative of the nucleosides (1) with -cyanoethyl phosphate and DCC or TPS-Cl. The same method has been used to phosphorylate iV -benzoylated 2, 3 -0,C -isopropylidene derivatives of various 5 -C-alkyladenosine species (2) and also 4 -allyladenosine (3) as part of a study in which derivatives of AMP... 

---