Approaches carbohydrate synthons

Recent developments in the enzymatic synthesis of carbohydrates can be classified into four approaches 1) asymmetric C-C bond formation catalyzed by aldolases (1-10 2) enzymatic synthesis of carbohydrate synthons (loll) 3) asymmetric glycosidic formation catalyzed by glycosidases (12.-17) and glycosyl transferases (18-23.) and 4) regioselective transformations of sugars and derivatives (24-25). These enzymatic transformations are stereoselective and carried out under mild conditions with minimum protection of functional groups. They hold promise in preparative carbohydrate synthesis. In connection with this book, we focus on the first two approaches. 

General Three Carbon Chiral Synthons from Carbohydrates Chiral Pool and Chiral Auxiliary Approaches... 

Corey (E.J Corey Pure Appl Chem 1969,14, 30) introduced the term synthon in 1969 when he published his innovative strategies for the construction of complex molecules by considering a retrosynthetic analysis. Later on, Hanessian s (Total Synthesis of Natural Products The Chiron Approach Pergamon Press, 1983) introduction in 1983 of the term Chiron referring to chiral synthons became the general strategy of carbohydrate like symmetry in new molecular targets of many natural products. 

This approach has been rapidly put into new concepts and reviewed. The Chiron approach concept was introduced by Hanessian in a review [4] and, in more detail, in his book [15]. The carbohydrate is considered as a chiral synthon, which has to be found retrosyntheticaUy in a... 

The presented review describes total syntheses directed towards 6-amino-6,8-dideoxy-D-eryt/iro-D-galacto-octose, commonly named lincosamine - the sugar component of the antibiotic lincomycin. In the first part we present total syntheses of lincosamine that start from carbohydrate precursors. The D-galactose-derived aldehyde is the most frequently used synthon. In the second part, total syntheses of lincosamine from non-carbohydrate precursors are presented. This part of the review is divided into two subsections. The first one groups syntheses based on the application of furan compounds. In the second one we present a hetero-Diels-Alder approach to the synthesis of lincosamine. 

Although most synthetic approaches to L-daunosamine start from carbohydrate precursors, some routes employ chiral synthons derived from other sources. The aldehydes 213 obtained through reaction of cinnamaldehyde with acetaldehyde in the presence of Baker s yeast followed by ozonolysis [157], and 214 obtained from L-tartaric acid [158-160] have been utilised in the synthesis of daunosamine derivatives, and protected daunosamines and acosamines have been synthesised from (synthetic approaches have employed lactic acid as a chiral starting material [162, 163] and the (S)-amine 215 obtained by resolution has been converted to V-benzoyl daunosamine together with its 3-epimer [164]. Wovkulich and Uskokovic have... 

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