Synthesis of truncated analogues for studying the process of glycosyl phosphatidylinositol modification

Many eukaryotic proteins are modified with a glycosylphosphatidylinositol (GPI) anchor at their C-termini. This post-translational modification causes these proteins to be noncovalently tethered to the plasma membrane. The synthesis of truncated GPI anchor analogues is reported; these compounds were designed for use as soluble substrates for GPI transamidase (GPI-T), the enzyme that appends the GPI anchor onto proteins.

Synthesis of novel DC-SIGN ligands with an alpha-fucosylamide anchor

The dendritic cell-specific intercellular adhesion molecule (ICAM) 3-grabbing nonintegrin (DC-SIGN) is a C-type lectin that appears to perform several different functions. Besides mediating adhesion between dendritic cells and T lymphocytes, DC-SIGN recognizes several pathogens some of which, including HIV, appear to exploit it to invade host organisms. The intriguing diversity of the roles attributed to DC-SIGN and their therapeutic implications have stimulated the search for new ligands that could be used as biological probes and possibly as lead compounds for drug development. The natural ligands of DC-SIGN consist of mannose oligosaccharides or fucose-containing Lewis-type determinants. Using the known 3D structure of the Lewis-x trisaccharide, we have identified some monovalent alpha-fucosylamides that bind to DC-SIGN with inhibitory constants 0.4-0.5 mM, as determined by SPR, and have characterized their interaction with the protein by STD NMR spectroscopy. This work establishes for the first time alpha-fucosylamides as functional mimics of chemically and enzymatically unstable alpha-fucosides and describes interesting candidates for the preparation of multivalent systems able to block the receptor DC-SIGN with high affinity and with potential biomedical applications.

A simple access to lactose-derived building blocks required in glycoconjugate synthesis

Lactose was readily transformed into thexyldimethylsilyl (3,4-O-isopropylidene-beta-D-galactopyranosyl)-(1-->4)-beta- D-glucopyranoside (5); this compound served as intermediate for the generation of partially O-protected lactose building blocks required in oligosaccharide and glycoconjugate synthesis. Thus, from 5 via per-O-benzoylation, desilylation, trichloroacetimidate formation, glycosylation of the Lemieux spacer, and acid-catalyzed de-O-isopropylidenation methoxycarbonyloctyl (2,6-di-O-benzoyl-beta-D-galactopyranosyl)- (1-->4)-2,3,6-tri-O-benzoyl-beta-D-glucopyranoside (12) was obtained. Regioselective benzoylation of 5 with benzoyl cyanide under various conditions afforded 3-O- (13), 2,3,2'-O- (14), 3,2'-O- (16), and 2,2'-O-unprotected (17) lactoside, respectively. De-O-isopropylidenation of 16 gave thexyldimethylsilyl (6-O-benzoyl-beta-D-galactopyranosyl)-(1-->4)-2, 6-di-O-benzoyl-beta-D-glucopyranoside (18), an important 2',3',4'-O-unprotected lactose derivative. Fucosylation of 13 and then de-O-isopropylidenation afforded thexyldimethylsilyl 2,6-di-O-benzoyl-beta-D-galactopyranosyl)-(1-->4)-[(3,4-di-O-acetyl-2-O- benzoyl-alpha-L-fucopyranosyl)-(1-->3)]-2,6-di-O-benzoyl-beta-D- glucopyranoside (21), an important fucosyllactose building block.