Current Organic Chemistry - Volume 18, Issue 14, 2014

This review discusses concepts towards facile non-enzymatic glycosylation of unprotected or lightly protected glycostructures. These comprise approaches in which reactivity distinction of hydroxyl groups is achieved via stannylene or boronic and borinic acid intermediates as well as via oxyanion formation along with syntheses based on selectivity implemented by the substrates themselves. Further, syntheses of complex glycostructures and oligosaccharides are shown, as well as the concept of random glycosylation towards glycoside libraries with desired equal product distribution.

6-Deoxyheptoses are rare higher-carbon sugars isolated from lipopolysaccharides (LPS) and capsular polysaccharides (CPS) of some Gram-negative bacteria (Campylobacter, Yersinia, Burkholderia, Eubacterium, Plesiomonas, and Escherichia species). They occur in numerous structural variations of the bacterial polysaccharides (PS), which are briefly summarized. Biochemical pathways involving deoxygenation of heptoses as well as possible approaches towards the chemical synthesis of these unusual monosaccharides will be discussed. The most important methods for the preparation of 6-deoxyheptoses include elongation of pentose or hexose chains by nucleophilic substitution, Wittig-type reaction, and nucleophilic addition into carbonyl group.

Only four nitro sugars have been identified in Nature and these occur in a range of natural products with antibiotic and anticancer activities. In some cases the nitro sugars are essential binding elements, but precise information on molecular recognition is lacking. Nitro sugars have developed into important synthetic tools. Particular emphasis is placed on carbon-carbon bond formations by means of Henry, Michael and cycloaddition reactions, and on the transformation of the nitro group to an amino group. This review mainly covers the literature from 2008 onwards.

Crystalline complexes of native cyclodextrins are of high interest due to their possible applications in various branches of industry. The encapsulation of active compounds by cyclodextrins results in a change of their properties, e.g. water solubility and bioavailability. Currently available native cyclodextrins inclusion complexes with biorelevant molecules in the solid state solved by X-ray crystallography are characterized. Studied guest compounds include aromas belonging to the family of terpenes and various drug molecules.

In this account, selected applications of monosaccharides, starting from sugar-based crown-ethers, in recognition of chiral ammonium cations derived from chiral amines and amino acids, are presented. The influence of sugar incorporation into the crown ether ring on binding and structural properties is discussed as well as selected methods used in determination of chiral recognition ability of these hosts. Afterwards, the differences in the design of hosts for chiral anions and receptors for cations are compared. The key-factors in construction of the sugar-based anion receptors: the structure of anion binding pocket and the role of sugar moiety, are shown. Application of these hosts in recognition of biologically important N-protected amino acids and α-hydroxy-acids, using titrations methodology under 1H NMR, UV/VIS and fluorescence control is reviewed.

The existing methodologies for the synthesis of 6-, 5-, 4-, 3-, 2-deoxysugars and functionalized branched-chain sugars at C-6, C-5, C-4, C-3, C-2 positions were compiled and reviewed.

This review concerns selected methods for the synthesis of uronic acids and uronic acid-containing oligosaccharides. Construction of uronic acids is broadly represented by methods based on carbohydrates and non-carbohydrates as well as de novo synthesis. Oxidation of carbohydrates is presented for both monosaccharides and oligosaccharides by using various methods including TEMPObased protocols.