Carbohydrates, branched-chain functionalized

A useful application of the chemistry shown in Scheme 83 is the synthesis of branched-chain functionalized carbohydrates. For this purpose two epoxides 261 and 262 derived from D-glucose and 263 derived from D-fructose were prepared following reported methodologies, and were submitted to a DTBB-catalyzed lithiation as described above in Scheme 83. The expected intermediates 264-266 and final products 267-269 were prepared in a regio- and stereoselective manner in 15- 95% yield" Also here, the use of a prochiral electrophile gave equimolecular amounts of both diastereomers. 

The Michael-type addition reaction of carbon nucleophiles to vinyl sulfone-modified carbohydrates should be considered as an efficient route for the synthesis of branched-chain sugars because almost all carbohydrates in pyranose and furanose form could be converted to their vinyl sulfone derivatives very easily [5, 12-14]. Moreover, the product of the reaction carrying sulfone functionality has the potential to undergo a wide variety of transformations [15]. For a review on desulfonylation reaction, see Ref. [16]. 

Chain-extension reactions via aldehyde additions have been used to synthesize higher aldoses, enuloses, branched-chain enuloses and 1-deoxy-alduloses. Addition of 2-lithio-1,3-dithiane to partially blocked carbohydrate derivatives proceeds in certain cases with high stereoselectivity the authors suggest that the reaction is controlled by chelation of the oxygen functions at C-1, C-2, and C-4... 

Grisebach, H., Branched-chain sugars Occurrence and biosynthesis, in Carbohydrates Stracture and Function (J. Preiss, ed.), Vol. 3 of The Biochemistry of Plants (P. K. Stumpf and E. E. Conn, eds.), 171-197, Academic Press, New York, 1980. 

A branched chain polysaccharide composed of glucose units. It functions as a storage form of carbohydrate in muscle, liver and other tissues. The glucose units are joined together in a-1,4 linkages except at the branch points where there is an a-1,6 linkage. 

The stereoselectivity of intermolecular free radical reactions has been reviewed including the use of carbohydrate-based radicals for forming branched-chain sugars. A number of intramolecular radical cyclisations affording C-branched compounds have been reported. A 2-deojgr-2-iodo-glycoside on treatment with Bu3SnH affords a C-2 radical which may cyclise onto an appropriate functional... 

Thiamin functions as the coenzyme TDP in the metabolism of carbohydrates and branched-chain amino acids (a-keto-isocaproic, a-keto-yS-methyl valeric, and a-keto-isovaleric acids). In association... 

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