Glycosyl phosphites as glycosylation reagents

In situ preactivation strategies for the expeditious synthesis of oligosaccharides: A review

Carbohydrates have gained increasing appreciation over the last few decades for their fundamental roles in all essential areas of life. As a result, there has been a surge of activity in synthetic glycosylation strategies to construct useful oligosaccharides. This review evaluates the advances in synthetic carbohydrate chemistry, specifically preactivation methodologies, stereoselective β-mannosylations, and an automated, electrochemical preactivation method. Also discussed is the use of preactivation as a tool to study reactive intermediates, and applications of preactivation protocols in the one pot-synthesis of a hyaluronic acid decasaccharide and one-pot synthesis of a tristearoyl lipomannan containing a pseudotrisaccharide.

Chemical synthesis of linear and cyclic unnatural oligosaccharides by iterative glycosidation of ketoses

The development of an efficient method for the stereoselective synthesis of alpha-D-(2-->1)-linked ketoside oligomers is described. The method is based on an iterative protocol composed of two key steps: a) the coupling of a thiazolylketosyl phosphite donor with an hydroxymethylketoside acceptor; and b) the introduction of the hydroxy-methyl group at the anomeric carbon atom of the resulting oligomer. To highlight its efficiency, the protocol was used in the assembly of D-galacto-2-heptulopyranose-containing oligoketosides through alpha-(2-->1) linkages up to the pentameric stage. The yield of the isolated oligomers ranged from 48 % in the first cycle to 29% in the fourth cycle. Having employed a pentenyl-substituted hydroxymethylketoside acceptor in the first cycle, all the derived oligomers contained the pentenyl group at their reducing end. This group was exploited to transform the linear oligomers into cyclic products through intramolecular glycosidation. The major product derived from the linear trisaccharide was confirmed by X-ray crystallography to be the cyclotris-(2-->1)-(alpha-D-galacto-2-heptulopyranosyl). The structure of this compound was essentially that of a [9]crown-3 ether bearing three galactopyranose rings spiroanellated in a propellerlike fashion. This arrangement of carbohydrate units linked to the crown ether created a densely alkoxylated cavity suitable for the encapsulation of alkali-metal cations (Li, Na, K, Ca, Mg).

Synthesis of beta-D-arabinofuranosyl-1-monophosphoryl polyprenols: examination of their function as mycobacterial arabinosyl transferase donors

A convenient synthetic strategy has been developed to produce libraries of beta-D-arabinofuranosyl-monophosphorylpolyprenol. Those containing C50 and C55 polyprenols were the most active as donors for the cell-free synthesis of the arabinans of mycobacterial cell walls.

Intervention of carbohydrate recognition by proteins and nucleic acids

Carbohydrates in biological systems are often associated with specific recognition and signaling processes leading to important biological functions and diseases. Considerable efforts have been directed toward understanding and mimicking the recognition processes and developing effective agents to control the processes. The pace of discovery research in glycobiology and development of carbohydrate-based therapeutics, however, has been relatively slow due to the lack of appropriate strategies and methods available for carbohydrate-related research. This review summarizes some of the most recent developments in the field, with particular emphasis on work from our laboratories regarding the use of chemoenzymatic strategies to tackle the carbohydrate recognition problem. Highlights include the study of selectin-carbohydrate and aminoglycoside-RNA interactions and development of agents for the intervention of these recognition processes.