Synthesis of new sulfonic acid-containing oligosaccharide mimetics of sialyl Lewis A

Two trisaccharides as new sulfonic acid mimetics of the sialyl Lewis A tetrasaccharide were synthesized. The natural sialic acid residue is replaced by a C-sulfonic acid moiety attached to position C-3′ of the lactosamine unit of the mimetics. The l-fucose unit was also replaced by a d-arabinose ring in one of the analogues. Formation of the sulfonic acid moiety on the trisaccharide level could be successfully achieved by means of introduction of an acetylthio moiety into the galactose skeleton and subsequent oxidation. The equatorial arrangement of the acetylthio group linked to C-3 of the galactose ring could be achieved by double nucleophilic substitution; efficient formation of the gulo-triflate derivatives required low-power microwave activation. Oxidation of the acetylthio group was carried out using Oxone in acetic acid.     

Parallel Synthesis of Sialyl Lewis X Mimetics on a Solid Phase: Access to a Library of Fucopeptides

A novel anchoring group p-(acyloxymethyl)benzylidene acetal (p-AMBA) enables the bidirectional functionalization of glycosylated amino acid derivatives and thus the rapid parallel synthesis of fucopeptides as sialyl Lewis X mimetics on a solid phase [Eq. (a), PEG-PS=poly(ethylene glycol) graft copolymer]. This led to the discovery of new mimetics against P-selectin with IC₅₀ values in the low μM range.     

Design and Synthesis of Carbohydrate Mimetics: A New Strategy for Tackling the Problem of Carbohydrate-Mediated Biological Recognition

Carbohydrates have been known as poor candidates for drug development. Recent studies have, however, shown that structurally simplified small molecules as mimics of complex carbohydrates recognized by receptors can be developed as inhibitors of carbohydrate-mediated biological recognition. In addition, small molecules with higher affinity and specificity than the parent ligands can be developed by incorporating additional hydrophobic or charged groups in the carbohydrate mimetic which contains essential functional groups for receptor binding. Representative examples are illustrated in the studies of sialyl Lewis x - selectin interactions, glycosidase and glycosyltransferase reactions and aminoglycoside antibiotic - RNA interactions.     

Synthesis of three fluorescent boronic acid sensors for tumor marker Sialyl Lewis X in cancer diagnosis

Sialyl Lewis X (sLex) is a carbohydrate that is considered not only a marker for cancer, but also an antigen associated with the malignant behavior of cancerous cells. We have synthesized three fluorescent boronic acid sensors as potential sensors for sLex. Photoinduced electron transfer by a fluorescence analyzer was used to assess sensor-sLex antigen binding. The reaction was carried out in mixed aqueous solution, and Sensor 3 was identified as showing the strongest fluorescence enhancement upon binding to sLex at 10 nM. In cell-line culture experiments, Sensor 1 was shown to label sLex expression positively for HepG2, Colo 205, and COS-7 cells, and negatively for MDA-MB-231 cells; Sensor 2 did so positively for HepG2, PLC/PRF/5, and Colo 205 cells, and negatively for MDA-MB-231 and COS7 cells; and Sensor 3 did so positively for PLC/PRF/5 and HepG2 cells, and negatively for MDA-MD-231 and COS7 cells. MTT cytotoxicity experiment results showed that the three sensors are nontoxic, and Hoechst 33258 experiments showed that no apoptosis occurred.     

Analysis of sialyl oligosaccharides by high-performance liquid chromatography-electrospray ionisation-mass spectrometry with differentiation of alpha2-3 and alpha2-6 sialyl linkages

A method for analysing sialyl oligosaccharides from bovine colostrum using high-performance liquid chromatography-electrospray ionisation-mass spectrometry (HPLC-ESI-MS) is described. Under positive ionisation mode, mass spectra of alpha2-3 and alpha2-6 linkages were different, and the former produced a prominent B2 (or B3 in disialyl lactose) mass fragment. This fragment was absent from mass spectra with alpha2-6 linkages. Two sialyl oligosaccharides, which have not been reported previously, were tentatively identified. One comprises a N-acetyl neuraminic acid (Neu5Ac), two hexoses (Hex), and one N-acetyl hexosamine (HexNAc) residue ((Neu5Ac)1 (Hex)2 (HexNAc)1), and the other comprises one Neu5Ac and one Hex residue ((Neu5Ac)1(Hex)1).     

Synthesis and Antigenic Property of a Novel Sialyl 6‐O‐Sulfo Lewis X Neo‐glycolipid Containing Lactamized Neuraminic Acid

Abstract

Synthesis and antigenic property of a novel 6‐O‐sulfated sLe^x neo‐glycolipid containing lactamized neuraminic acid are described. Coupling of methyl (methyl 4,7,8,9‐tetra‐O‐acetyl‐3,5‐dideoxy‐5‐trifluoroacetamido‐D‐glycero‐α‐D‐galacto‐2‐nonulopyranosylonate)‐(2→3)‐4,6‐di‐O‐acetyl‐2‐O‐benzoyl‐1‐thio‐β‐D‐galactopyranoside (3) with 2‐(tetradecyl)hexadecyl (2,3,4‐tri‐O‐benzyl‐α‐L‐fucopyranosyl)‐(1→3)‐2‐acetamido‐2‐deoxy‐6‐O‐4‐methoxyphenyl‐β‐D‐glucopyranoside (7) gave a protected sLe^x tetrasaccharide glycolipid (8). Removal of all the acyl protecting groups and subsequent lactamization afforded the lactamized sLe^x derivative(10), which was converted to the target compound (14) by selective removal of the 4‐methoxyphenyl group and 6‐O‐sulfation of the GlcNAc residue, and removal of all protective groups under the basic conditions furnished the target molecule. The antigenic property of the synthesized neo‐glycolipid was examined by TLC‐immunostaining with G159 monoclonal antibody.     

Humoral response against sialyl‐Lea glycosylated protein species in esophageal cancer: Insights for immunoproteomic studies

Esophageal cancers (ECs) show poor prognosis and decreased overall survival due to late diagnosis and ineffective therapeutics, urging the introduction of novel biomarkers to aid disease management. The levels of sialyl‐Lewis(a) antigen (sLe^a) are frequently increased in digestive tumours, which has been explored in serological non‐invasive prognostication (CA19‐9 test); however, with low sensitivity and specificity. Autoantibodies against cancer antigens are considered the next generation biomarkers, as they are present in circulation long before tumour‐associated proteins. Based on these observations we have mined the serum of EC patients (n = 7) for antibodies against sLe^a‐glycosylated protein species. All EC were positive for sLe^a, irrespectively of their histological nature but only two patients showed elevated CA19‐9. Moreover, IgG titers, with emphasis on IgG1, were elevated in EC patients in comparison to the control group. SLe^a‐glycoproteins were then extracted from tumours of patients with negative CA19‐9, isolated by immunoprecipitation and blotted with patients IgG. Autoantibodies against sLe^a‐glycosylated proteins were detected in all cases. Different SLe^a‐glycoproteins were observed for tumours of distinct histological natures, which now require identification and validation in larger patient sets. This preliminary data suggests that antoantibodies against sLe^a glycosylated proteins hold potential for non‐invasive diagnosis in CA19‐9 negative cases and sets the rational for future immunoproteomic studies envisaging highly specific EC biomarkers.