Carbohydrates in synthesis

O-protected cyclic or acyclic carbon frameworks. The choice of acetals or ethers as derivatives allows a systematic manipulation of diols and polyols. Kinetic control and a lesser affinity for protonation on sulfur compared with oxygen allows the transformation of cyclic hemiacetals into acyclic dialkyl dithioacetals. Acetal, ether, and dithioacetal derivatives are some of the pivotal intermediates needed to explore various applications of carbohydrates in synthesis. 

O. S. Chizhov, Uglevody v Sinteze Prirodnykh Soedinenii (Carbohydrates in Synthesis of Natural Compounds). Nauka, Moscow, 1984. 

The most stable protected alcohol derivatives are the methyl ethers. These are often employed in carbohydrate chemistry and can be made with dimethyl sulfate in the presence of aqueous sodium or barium hydroxides in DMF or DMSO. Simple ethers may be cleaved by treatment with BCI3 or BBr, but generally methyl ethers are too stable to be used for routine protection of alcohols. They are more useful as volatile derivatives in gas-chromatographic and mass-spectrometric analyses. So the most labile (trimethylsilyl ether) and the most stable (methyl ether) alcohol derivatives are useful in analysis, but in synthesis they can be used only in exceptional cases. In synthesis, easily accessible intermediates of medium stability are most helpful. 

Even though acetate units, such as those obtained from fatty acid oxidation, cannot be used for net synthesis of carbohydrate in animals, labeled carbon from " C-labeled acetate can be found in newly synthesized glucose (for example, in liver glycogen) in animal tracer studies. Explain how this can be. Which carbons of glucose would you expect to be the first to be labeled by "Relabeled acetate ... 

Compounds in carbohydrate-based synthesis of 2,3-dihydro-4//-pyranones as starting compounds for the preparation of C-saccharides, glycosylstan-nanes, and analogs of tromboxane A2. 98EJ02267. 

Therefore, taking into account the potentialities of such lactones as carbohydrate delivery synthons (vide infra), several routes leading to carboxymethyl glycosides (and thus subsequently to the lactones) were investigated, in order to get as many structural variations as possible for widening the scope of their use in synthesis. In addition to the isomaltulose oxidation method (route a), the oxidation of allyl glycosides (route b), and the anomeric alkylation with tert-butylbromoacetate (route c) were studied (Scheme 11). These three methods are detailed in the following sections. 

The regio- and stereo-selective functionalization of aldonolactones yields optically active lactones, which are important precursors in natural product synthesis. Concepts such as chiral templates and chirons, derived from carbohydrates, have been ingeniously and widely applied in synthesis (233). Among the commercially available aldonolactones, D-ribono-1,4-lactone is... 

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