Allose synthesis

Figure 2. Synthesis of 6-deoxy-2-0-methyl-D-allose (javose).

Allitol was characterized by its melting point, 149-150°, elementary analysis, and by the formation of a dibenzylidene derivative, which, after recrystallization from alcohol, melted at 249-250° on the Maquenne block. Later, Steiger and Reichstein7 repeated this synthesis of allitol and demonstrated the identity of the product with that obtained by the reduction of D-allose. 

The potentialities of this method are such that, with the proper choice of hexofuranose derivative, access can be gained to 2,5-anhydroaldoses in which the side chains have the cis orientation, as would be required for further elaboration into C-nucleosides. Matsui and coworkers62 reported the synthesis of modified C-nucleosides by acidic treatment of 3-0-benzyl-l,2-0-isopropylidene-5,6-di-0-(methylsulfonyl)-/3-L-talofuranose (60), to give 2,5-anhydro-3-0-benzyl-6-0-(methylsulfonyl)-aidehydo-D-allose dimethyl acetal (61). 

Another method of synthesis of derivatives of 3-methyl-D-glucose lies in the scission of the anhydro-ring of 2,3-anhydro-D-allose derivatives with sodium methoxide, when the entry of the methoxyl group is accompanied by a Walden inversion on C3.82... 

Carbohydrates.—The acid (87), an intermediate in the synthesis of oxaprostaglandin derivatives from D-ribofuranose sugars,84 is obtained from the aldehyde (88) and the sodium salt of (79). The condensation of 2,5-anhydro-D-allose derivatives with (89) gave the expected products (90).85 Similarly, 1,4-furanoses (91) afford (92).86 These unsaturated halides are useful intermediates for further modifications. 

This interesting transformation from a readily available 6-deoxyhexose forms the basis for the synthesis231 of 6-deoxy-2,3-di-0-methyl-D-allose (mycinose),168 one of the carbohydrate moieties of the antibiotic chalco-mycin. The synthesis merely involves the protection of the C-5 hydroxyl group in (41) by benzylation, followed by partial hydrolysis with acid, methylation of the product at the C-2 and C-3 hydroxyl groups, and debenzylation. 

R. U. Lemieux Application of nuclear magnetic resonance to problems of structure, configuration, and conformation in carbohydrate chemistry J. S. Brimacombe Synthesis of some naturally occurring allose derivatives and some associated chemistry... 

J. G. Buchanan, D. M. Clode, and N. Vethaviyasar, Potential hexokinase inhibitors. Synthesis and properties of 2,3-anhydro-D-allose, 2,3-anhydro-D-ribose, and 2-0-methylsulphonyl-D-mannose, J. Chem. Soc., Perkin Trans. 1, (1976) 1449-1453. 

Another highly versatile building block derived from diacetone-glucose 54 is the 1,2-acetonide of 3-C-methyl-a-D-allose in its furanoid form 57, which has been utilized as the key compound in a convergent total synthesis of ACRL Toxin I (63). Its elaboration from 54 starts with a pyridinium dichromate / acetic anhydride oxidation (64), is followed by carbonyl olefination of the respective 3-ulose with methyl (triphenyl)phosphonium bromide and hydrogenation (— 55 56), and is completed by acid cleavage of the 5,6-isopropylidene group. This four-step process 54 -> 57, upon optimization of reaction conditions and workup procedure, allows an overall yield of 58 % (63), as compared to the 22 % obtained previously (65). 

The utilization of the furanoid 3-C-methyl-D-allose building blocks 57 and 60 for a convergent total synthesis of ACRL Toxin I in the form of its stable 3-0-methyl ether (63) involved their conversion into enantiomerically uniform connective segments. The key feature of the retrosynthesis was the expectation... 

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