Anti-adhesive therapeutics: A new class of anti-inflammatory agents

Novel mimics of sialyl Lewis X: design, synthesis and biological activity of a series of 2- and 3-malonate substituted galactoconjugates

A series of potent inhibitors of P-selectin as potential anti-inflammatory agents is reported. These compounds are derivatives of galactocerebrosides bearing a malonate side chain in positions 2 and 3 of the galactose moiety. Based on the binding mode of sialyl Lewis X, the two acidic groups of the malonate are designed to form ionic interactions with two important lysines in the active site of P-selectin, Lys113 and Lys111. On the other hand, the 4- and 6-hydroxy groups on the galactose ring are arranged to chelate the calcium ion in the P-selectin active site. The synthesis and the biological activity of this series of compounds are described. Lead compounds having a greater potency than sialyl Lewis X are identified.

Minimal sulfated carbohydrates for recognition by L-selectin and the MECA-79 antibody

Sulfated forms of sialyl-Le(X) containing Gal-6-SO(4) or GlcNAc-6-SO(4) have been implicated as potential recognition determinants on high endothelial venule ligands for L-selectin. The optimal configuration of sulfate esters on the N-acetyllactosamine (Galbeta1-->4GlcNAc) core of sulfosialyl-Le(X), however, remains unsettled. Using a panel of sulfated lactose (Galbeta1-->4Glc) neoglycolipids as substrates in direct binding assays, we found that 6',6-disulfolactose was the preferred structure for L-selectin, although significant binding to 6'- and 6-sulfolactose was observed as well. Binding was EDTA-sensitive and blocked by L-selectin-specific monoclonal antibodies. Surprisingly, 6', 6-disulfolactose was poorly recognized by MECA-79, a carbohydrate- and sulfate-dependent monoclonal antibody that binds competitively to L-selectin ligands. Instead, MECA-79 bound preferentially to 6-sulfolactose. The difference in preferred substrates between L-selectin and MECA-79 may explain the variable activity of MECA-79 as an inhibitor of lymphocyte adhesion to high endothelial venules in lymphoid organs. Our results suggest that both Gal-6-SO(4) and GlcNAc-6-SO(4) may contribute to L-selectin recognition, either as components of sulfosialyl-Le(X) capping groups or in internal structures. By contrast, only GlcNAc-6-SO(4) appears to contribute to MECA-79 binding.

Studies on selectin blockers. 7. Structure-activity relationships of sialyl Lewis X mimetics based on modified Ser-Glu dipeptides

We have previously found that heterochiral fucodipeptides, L-Ser-D-Glu (3a) and D-Ser-L-Glu (3b), exhibited up to 20-100 times more potency than a sialyl Lewis X (sLeX, 1) and a 3'-sulfated Lewis X analogue (2) toward E-selectin binding and have also proposed, from molecular dynamics calculation, that their strong activities would depend on a possible formation of the type II and/or type II' beta-turn of compounds 3a,b (Tsukida, T.; Hiramatsu, Y.; Tsujishita, H.; Kiyoi, T.; Yoshida, M.; Kurokawa, K.; Moriyama, H.; Ohmoto, H.; Wada, Y.; Saito, T.; Kondo, H. J. Med. Chem. 1997, 40, 3534-3541). To clarify our hypothesis, we synthesized several analogues of compounds 3a,b and investigated their structure-activity relationships. As a result, it was indicated that the type II and/or type II' beta-turn conformation would be a comparatively tight form and would play important roles in favorable binding to E-selectin. These findings indicate that sLeX mimetics with type II and type II' beta-turn dipeptides could be a useful methodology for the design of an active selectin blocker.

Studies on selectin blockers. 6. Discovery of homologous fucose sugar unit necessary for E-selectin binding

We describe a mimic of the sugar unit of the E-selectin ligand, sialyl Lewis X (sLeX). Carbohydrates are entering the realm of rational drug design, aided by the growing understanding of the structure-function relationships. We investigated a new methodology of preparing sLeX mimetics and developed a potent E-selectin blocker characterized by beta-turn dipeptides. Another characteristic point of this E-selectin blocker is that the six-membered fucose ring was replaced with a five-membered fucose ring. Interestingly, it was found that the five-membered fucose ring could also bind to a calcium ion on the E-selectin, which could be an important role of the six-membered fucose ring. Especially, the L-Ser-D-Glu and D-Ser-L-Glu derivatives 3a,b showed 65-90-fold more potent inhibitory activities than the sulfated LeX analogue 1. In addition, molecular dynamics (MD) studies indicated that the 2- and 3-OH groups of the six-membered fucose ring, which were necessary for the calcium binding, overlapped well with the 2- and 3-OH groups of the five-membered fucose ring. These new findings could be useful for the design of new types of selectin blockers.

Chemical approaches to glycobiology and emerging carbohydrate-based therapeutic agents

The contributions of cell surface oligosaccharides to critical biological processes such as leukocyte-endothelial cell adhesion, bacterial and viral infection, and immunological recognition of tumor cells and foreign tissue are now understood in significant molecular detail. These discoveries at the forefront of biological research have motivated the design of synthetic glycoconjugates as tools for the fundamental study of glycobiology and as candidates for future generations of therapeutic and pharmaceutical reagents. During the past two years, significant progress has been made in the design and synthesis of carbohydrate-based inhibitors of selectins, receptors involved in the attachment of leukocytes to endothelial cells at sites of inflammation. Monomeric and multivalent oligosaccharides that bind to bacterial and viral receptors have been shown to abrogate infection by agents such as Helicobacter pilori, influenza virus and HIV. The identification of certain cell surface oligosaccharides as potent antigens has prompted their use in tumor vaccines, and inspired new approaches to the management of tissue rejection subsequent to xenotransplantation. To better understand how cell surface oligosaccharides function within their native context, novel chemical approaches to modulating cell surface oligosaccharides structures are now being developed. These stratergies for cell surface 'glycoform remodeling' promise to facilitate the investigation of carbohydrate mediated cell-cell interactions.

Convenient chemoenzymatic synthesis of beta-purine-diphosphate sugars (GDP-fucose-analogues)

A series of peracetylated beta-sugar-1-phosphates with L-fuco configuration are efficiently prepared chemically and coupled in high yields to purine monophosphate bases via imidazolide activation. The resulting purine diphosphate sugars are deacetylated completely by a mild treatment with commercial acetylesterase (EC 3.1.1.6) to give donor-substrates for fucosyl-transferases.

Mimics of the sialyl Lewis X tetrasaccharide. Replacement of the N-acetylglucosamine sugar with simple C2-symmetric 1,2-diols

Analogues of sialyl Lewis X have been synthesized that feature replacement of the N-acetylglucosamine residue with C2-symmetric diols. The diols used contain different levels of torsional constraint and various functional groups. The cyclohexyl derived compound 27 was equipotent to sLex in vitro (IC50 0.5 mM).

Synthesis of a Sialyl Lewis x Mimic with Fixed Carboxylic Acid Group: Chemical Approach toward the Elucidation of the Bioactive Conformation of Sialyl Lewis x

The relation of the solution and bioactive conformation of sialyl Lewis x (sLe(x)) has been addressed by chemical means. To mimic the preferred solution conformation of sLe(x) 1, the more rigid analog 2 has been designed and synthesized. The sialic acid residue of 1 was replaced by a carboxylic acid function which is fixed in the equatorial position of a six membered ring acetal fused to galactose. Due to entropic considerations, an increased biological activity could be expected if the preferred solution conformation and bound form of sLe(x) were similar. Since mimic 2 was found to be inactive in an E-selectin binding assay, the bound form of sLe(x) most probably differs from the prevailing solution conformation.