Synthesis of monosaccharides and analogues Part two: chain elongation of aldehydes

摘要

In a series of three articles a selection of the most important methods for the asymmetric synthesis of monosaccharides and analogues of biological importance will be presented. Nowadays any natural and non-natural monosaccharide can be prepared pure in both enantiomeric forms starting from inexpensive starting materials. Depending on the target, pure chemical procedures relying upon asymmetric catalysis using either metallic or pure organic catalysts can be applied successfully, alone or in combination with chemoenzymatic methods. Alternative methods rely upon substrate- or reagent-controlled diastereo- and enantioselective reactions. By total synthesis the carbohydrates are delivered in suitably protected or semiprotected forms, thus allowing their direct use in the preparation of oligosaccharides and analogues. In contrast, by starting with natural sugars, this sometimes requires several delicate chemical operations. In this part we present applications of the most important procedures that have been developed to extend the carbon chain of aldehydes, including short aldoses, into monosaccharides and analogues of biological interest.