Publisher Summary This chapter provides an overview of the synthesis of branched-chain sugars. The naturally occurring, branched-chain sugars were classified as rare sugars until the 1960's, but the discovery of numerous new sugars as the glycosidic component of antibiotics during the past two decades has stimulated extensive research on their chemistry and biochemistry. Most of the branched sugars found in Nature have a polar substituent at the branching carbon-atom (Type A); tertiary alcohols are commonest, but some of them are in the form of a methyl ether, acetate, or cyclic carbonate and, in several instances, an amino or a nitro group is attached to the tertiary carbon atom. Diversity is observed in the branchings, but some of them are chemically interconvertible and also can be derived from a common intermediate. This chapter explains the concepts related to the nucleophilic reactions of sugar oxiranes, aldol addition, and cyclization of dialdehydes with nitroalkanes. It also presents a brief discussion on methyl-branched sugars and two-carbon-branched sugar.

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Synthesis of Branched-Chain Sugars

Branched-chain sugars have recently been isolated in larger numbers from microorganisms and higher plants as glycoside components of antibiotics or phenolic compounds They also occur in plants in cell wall polysaccharides Sugars with methyl, hydroxymethyl,formyl, hydroxyethyl, and glycoloyl branches have so far been found in nature Many new methods have been developed for the synthesis of these sugars With one exception, the branched sugars known at present can be divided biogenetically into three groups Sugars with methyl branches are formed by C1 transfer, sugars with hydroxyethyl branches by C2 transfer to a hexose chain, and sugars with hydroxymethyl or formyl branches by rearrangement of a hexose or pentose chain

Chemistry and biochemistry of branched-chain sugars.

Verzweigtkettige Zucker sind in jungerer Zeit in groserer Zahl aus Mikroorganismen und hoheren Pflanzen als glykosidische Bestandteile von Antibiotika oder phenolischen Verbindungen isoliert worden. In Pflanzen kommen sie auch in Polysacchariden der Zellwand vor. Bisher wurden Zucker mit Methyl-, Hydroxymethyl-, Formyl-, Hydroxyathyl- und Glykoloyl-Verzweigung in der Natur gefunden. Fur die Synthese dieser Zucker wurden zahlreiche neue Verfahren entwickelt. Mit einer Ausnahme lassen sich die bisher bekannten verzweigtkettigen Zucker biogenetisch in drei Gruppen einteilen. Zucker mit Methyl-Verzweigung entstehen durch C1-Ubertragung, hydroxyathyl-verzweigte Zucker durch C2-Ubertragung auf eine Hexosekette und Zucker mit Hydroxymethyl- oder Formyl-Verzweigung durch Umlagerung einer Hexose- oder Pentosekette.

Chemie und Biochemie verzweigtkettiger Zucker

Synthesis and properties of 3′-C-methylnucleosides and their phosphoric esters

Stereoselectivities in diazomethane and nitromethane reaction of methyl 2-O-benzoyl-4,6-O-benzylidene-α-D-ribo-hexopyranosid-3-ulose were examined. Reduction of the epoxidation product (2) gave an epimeric 3-C-methyl derivative in contrast with that obtained by the Grignard reaction. Comparison of NMR spectra of the corresponding di-O-acetate of the both epimers proved that 2 has the gluco-configuration. Ring-opening of the epoxide with alkali, methanolic ammonia, and acid gave the corresponding 3-C-hydroxymethyl, 3-C-aminomethyl (17), and de-O-benzylidenated product, respectively. Hydrogenation of the 3-C-nitromethyl derivative (21) obtained by nitromethane condensation, in the presence of Raney nickel, accompanied with benzoyl-migration to give 3-C-benzamidomethyl derivative (22). De-benzoylation of 22 with methanolic potassium hydroxide gave 3-C-aminomethyl derivative (26) and an orthoester-type compound. Comparison of 26 with 17 and their derivatives indicated that 21 has the allo-configuration. The b...

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Robert. Gasser

Papers

Addition of diazomethane to 1,2-O-isopropylidene-5-O-trityl-.alpha.-D-erythro-pentos-3-ulose