MinireviewRecent developments in β-C-glycosides: synthesis and applications
Graphical abstract
Introduction
In carbohydrate chemistry, a glycoside is an organic molecule in which sugar is bound to a non-carbohydrate moiety. Glycosides play several important roles in living organisms such as regulation of plant growth, cardiac muscle stimulant, and the primary function as the source of energy for organisms. Generally glycosides can be linked by an O-, N-, S- and C-glycosidic bonds. Intriguingly, C-glycosides are resistant to both acidic and enzymatic hydrolysis, where the other types of glycosides are unstable under hydrolytic conditions. S-Glycosides are also known to be resistant towards enzymatic hydrolysis, but on acidic hydrolysis it leads to the formation of free thiols with offensive odour. C-Glycosides were considered as stable pharmacophores and known to be used in the synthesis of enzyme inhibitors1 and drug molecules for certain viral diseases such as human immunodeficiency virus (HIV), hepatitis virus B and herpes viruses.2, 3 Biological activities of the carbohydrate moiety stood up because of its mien at the interface of the cell and its surroundings in bacteria, parasites, viruses, tumors and numerous other targets. This has led to the development of a vaccine by conjugating the carbohydrate with immunogenic carrier proteins using carbohydrate specific immune response concept. For example, a fully synthetic glycoconjugate vaccine has been developed against Haemophilus influenzae type b.4 In the field of material science, carbohydrate-based surfactants represent an increasingly important class of non-ionic surfactants/neutral surfactant such as alkyl polyglucosides (APGs) and sorbitan esters (trade names SPAN® and Tween®) which possess a number of favourable attributes including desirable detergent properties and low toxicity.5 However, carbohydrate-based surfactants generally incorporate either base-labile ester linkages (SPAN®, Tween®, and MGEs), or acid-labile O-glycosidic linkages (APGs) into their structures.6 The instability of these functionalities limits the application of carbohydrate-based surfactants in cosmetics, toiletries, agrochemicals and lubricants.7, 8, 9 One potential way to address this issue is to replace O-glycosidic linkage with a more stable C-glycoside linkage. In this review we discuss a decade of research focused on the synthesis of C-glycosides10 and their applications (Fig. 1).
Section snippets
Cross-coupling approach
Aryl-C-glycosides have an aryl ring directly connected to the sugar core that confers their stability towards the enzymatic and chemical hydrolysis. Consequently these molecules are of prodigious significance in medicinal chemistry. Moreover, the aryl ring in aryl-C-glycosides provides them an adequate intracellular lifetime to allow trafficking to the nucleus, where they bind to DNA thus forming stable complexes. They also possess antibacterial, antitumor and antifungal activities and are
Synthesis of sugar based macrolides
The pharmacological properties of macrocycles originate from their structural complexity, rigidity and ability to form stable, inter- and intramolecular hydrogen bonding.111, 112, 113, 114 In this context several research groups focused on the synthesis of carbohydrate based macrocycles that can form extensive hydrogen bonding networks.115, 116, 117, 118, 119 Biologically active macrolides such as kendomycin, bryostatin, spongistatine, rapamycin and clicktophycin inspire the synthesis of
Conclusion
Evidently the field of C-glycoside chemistry has received increasingly growing attention in the past four decades.185 Different synthetic approaches are currently available for the synthesis of C-glycosides from various functionalized sugar derivatives. A surplus of catalysts and promoters is available for this C-glycoside synthesis. Among the various available synthetic protocols, synthesis using β-C-glycosidic ketone is considered as highly versatile that led to a diverse array of interesting
Acknowledgements
S.N. thanks the Department of Science and Technology (IFA-CH-04 and #SB/FT/CS-024/2013), India and Board of Research in Nuclear Science [#37(1)/20/47/2014], Department of Atomic Energy, India for financial support. S.N. also thanks SASTRA University for TRR research fund. P.K.V. thanks Department of Biotechnology for the Ramalingaswami Re-Entry Fellowship. S.N. thank Dr. T. Mohan Das for his encouragement.
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