Polyols biological, reactions

New synthetic methods are the lifeblood of organic chemistry. Synthetic efforts toward natural products often provide the impetus for the development of novel methodology. Reactive synthons derived from 1,3-dioxanes have proven to be valuable intermediates for both syn- and anfz-1,3-diols found in many complex natural products. Coupling reactions at the 4-position of 1,3-dioxanes exploit anomeric effects to generate syu-1,3-diols (cyanohydrin acetonides), autz-1,3-diols (4-acetoxy-1,3-dioxanes), and either syn- or azztz-1,3-diols (4-lithio-1,3-dioxanes). In the future, as biologically active polyol-containing natural products continue to be discovered, the methods described above should see much use. 

Alditols polyols are readily renewable, inexpensive and harmless to the environment. By incorporation of polyols into aliphatic polyesters, functional linear or hyperbranched polymers can be prepared with specific biological activities and/or that respond to environmental stimuli. Polyesters with carbohydrate or polyol repeat units in chains have been prepared by chemical methods. " In some cases, the reaction conditions led to hyperbranched polymers (HBPs). The highly branched architecture of HBPs leads to unusual mechanical, rheological and compatibility properties. " These distinguishing characteristics have garnered interest for their use in numerous industrial and biomedical fields. Chemical routes to linear polyol-polyesters require elaborate protection-deprotection steps ". Furthermore, condensation routes to hyperbranched polymers generally require harsh reaction conditions such as temperatures above 150 C and highly acidic catalysts ". ... 

Site-selective deo>ygenation of biologically active polyols is an attractive transformation, which enables expansion of the structural diversity of the polyols and increases the opportunity to find biologically active analogues. Site-selective deojygenation of polyols was investigated by the sequence of site-selective thiocarbonylation and Barton-McCombie reaction. Site-selective thiocarbonylation of a-methyl glucoside 93 was examined with phenyl... 

Abstract Development and scope of conventionally difficult molecular transformation on site-selective acylation of carbohydrates and polyol compounds are described. A salient feature is that the site-selectivity can be controlled independently from the intrinsic reactivity of the substrate, i.e., catalyst-controlled selectivity. Therefore, some substrates undergo acylation with reversal of their intrinsic reactivity. The mechanistic aspects of catalyst-controlled site-selective acylation are discussed with the emphasis on the strategy relying on the accelerative reaction rather than the decelerative one. An unconventional retrosynthetic route based on catalyst-controlled site-selective acylation is proposed toward extremely short-step total synthesis of natural glycosides of an ellagitannin family. Application to the late-stage functionalization of the complex natural products of biological interest is also described. 

EIGURE 22.20 Polyols of a given triglyceride prepared via (a) epoxidation reaction and (b) hydrofoimylation reaction. With permission from Petrovic ZS. Polymers from biological oils. Contemp Mater 2010 I-l 39-50. 

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