Thiosugars: new perspectives regarding availability and potential biochemical and medicinal applications

Thiosugars, containing a sulfur atom as heteroatom or a disaccharide linked via a sulfur bridge, possess unique physicochemical properties such as water solubility, which differs from conventional functionalized monosaccharides. The differences in biological activities between thiosugars and their oxygen analogs depend on geometric, conformational, and flexibility differences. They depend also on their electronic differences, the sulfide function being less electronegative and more polarizable than the ethereal moiety. Many functionalized thiosugars occur naturally and are potential targets for the development of carbohydrate-based therapeutics. Among the few new examples of the potential new targets are salacinol and kotalanol, tagetitoxin, thiolactomycin and analogues, mycothiol and analogues, and S-nitrosothiols. These new developments and representative examples of functionalized thiosugar prototypes as potential new targets are presented in this mini review.

Functionalized S-thio-di- and S-oligosaccharide precursors as templates for novel SLex/a mimetic antimetastatic agents

Adhesive interactions between molecules expressed on vascular endothelium and circulating tumor cells are key early events in cancer metastasis. Best characterized to date is the selectin family of cell adhesion molecules, which can bind to and stabilize blood-borne cells on organ vasculature, facilitating the cell-cell and cell-substratum interactions leading to tumor seeding and proliferation. Major ligands of E-selectin, the selectin family member expressed on vascular endothelial cells, include sialylated, fucosylated glycans such as Sialyl Lewis type carbohydrate complexes (SLe(x) and SLe(a)). These carbohydrate antigens are ubiquitously expressed on tumor cells with high metastatic potential, including colon and pancreatic carcinomas, and have been found to selectively and avidly bind E-selectin. Compounds that prevent E-selectin-SLe(x/a)binding represent an attractive tool in the prevention of cancer dissemination. Review of preclinical in vitro and in vivo studies suggest that SLe(x/a) 'mimetics' may serve as a potent class of anti-metastatic compounds. These agents are designed to outcompete SLe(x/a) antigens expressed on tumor cell surfaces to prevent initial vascular adhesion. Critical in generating exogenous oligosaccharides as SLe(x/a) mimetics is the stereoselective joining of specific mono- and di- saccharides that express functional groups integral in E-selectin-SLe(x/a) binding. Employing sulfur linkages to couple saccharide units enhances the biological stability of these complex carbohydrates. The synthesis of novel S-thiodisaccharides and C-disaccharides as SLe(x/a) precursors using the chiral sugars levoglucosenone, isomeric isolevoglucosenone and their functionalized analogs is described. The highly stereoselective functionalization of both enones at the C-4, C-3 and C-2 positions by the set of Michael addition reactions of reactive 1-thiosugars is reviewed. These functionalized S-thio di- and S-oligosaccharide precursors have direct application for use as templates in the synthesis of novel SLe(x/a)mimetics.

Thio-sugars VII. Effect of 3-deoxy-4-S-(beta-D-gluco- and beta-D-galactopyranosyl)-4-thiodisaccharides and their sulfoxides and sulfones on the viability and growth of selected murine and human tumor cell lines

The first conversion of (1-->4)-thiodisaccharides into corresponding sulfoxides and sulfones by conventional oxidation with m-chloroperoxybenzoic acid (MCPBA) is reported. The effects of alpha-(1-->4)-3'-deoxythiodisaccharides (8-9) and their sulfoxide (14-15) and sulfone (16-17) derivatives on murine leukemia and human colon and pancreatic carcinoma cell viability were studied. Concentrations of thio-sugars that decreased tumor cell line viability by 50% (IC(50)), measured via the MTT assay, ranged from 6.4 to 38.3 microg/mL. The effect of alpha-(1-->4)-3'-deoxythiodisaccharide derivatives were most profound on human pancreatic epithelial carcinoma (PANC-1) cells with compounds 8 and 9 having IC(50) values of 6.4 microg/mL and 8.2 microg/mL, respectively. Sulfone derivatives 16 and 17 also had pronounced effects on PANC-1 cell viability (IC(50)=10.2 microg/mL and 9.6 microg/mL, respectively). These results indicate that deoxythio-disaccharide analogs generated by functionalization of the universal chiral precursor levoglucosenone may have cytotoxic properties and therapeutic potential as anticancer agents.

Thio sugars: biological relevance as potential new therapeutics

The biological relevance of sulfur containing carbohydrates is gaining substantial attention. Thus the new developments, especially in the synthetic and medicinal chemistry of thio-sugars are critically important for carbohydrate drug design. New studies of biological processes including biosynthetic reactions and enzyme control mechanisms, discovered during the last few years clearly contributed to an understanding of their biological roles. These roles of carbohydrates and thio-sugars in particular through biological processes and diseases are becoming better understood now. These new trends will provide tremendous opportunities for the development of carbohydrates as new potential drugs. The main objective of this article is to address these new promising advances

Thio Sugars: Biological Relevance as Potential New Therapeutics

Abstract:

The biological relevance of sulfur containing carbohydrates is gaining substantial attention. Thus the new developments, especially in the synthetic and medicinal chemistry of thio-sugars are critically important for carbohydrate drug design. New studies of biological processes including bio­ synthetic reactions and enzyme control mechanisms, discovered during the last few years clearly contributed to an understanding of their biological roles. These roles of carbohydrates and thio­ sugars in particular through biological processes and diseases are becoming better understood now. These new trends will provide tremendous opportunities for the development of carbohydrates as new potential drugs. The main objective of this article is to address these new promising advances and stimulate continuous development of carbohydrate pharmaceuticals.

Thio-sugars. IV: Design and synthesis of S-linked fucoside analogs as a new class of alpha-L-fucosidase inhibitors

alpha-1-Thio-L-fucose derivative 4 and 5 as new alpha-fucosidase inhibitors (K1 = 4.6, and 5.9 microM) have been synthesized in three steps by base catalyzed coupling with bromonitromethane followed by reduction of the nitro group with sodium borohydride/cobalt chloride complex and acetylation.