Robert D. Locke

Use of 1,2-dichloro 4,5-dicyanoquinone (DDQ) for cleavage of the 2-naphthylmethyl (NAP) group

Abstract The 2-naphthylmethyl (NAP) group is a versatile group for protection of hydroxyl functions. It is stable to 4% TFA in CHCl 3 , hot 80% HOAc–H 2 O, SnCl 2 –AgOTf and HCl–EtOH, but it can readily be removed with DDQ in CH 2 Cl 2 .

Fluorinated per-acetylated GalNAc metabolically alters glycan structures on leukocyte PSGL-1 and reduces cell binding to selectins

Novel strategies to control the binding of adhesion molecules belonging to the selectin family are required for the treatment of inflammatory diseases. We tested the possibility that synthetic monosaccharide analogs can compete with naturally occurring sugars to alter the O-glycan content on human leukocyte cell surface selectin-ligand, P-selectin glycoprotein ligand-1 (PSGL-1). Resulting reduction in the sialyl Lewis-X-bearing epitopes on this ligand may reduce cell adhesion. Consistent with this hypothesis, 50muM per-acetylated 4F-GalNAc added to the growth media of promyelocytic HL-60 cells reduced the expression of the cutaneous lymphocyte associated-antigen (HECA-452 epitope) by 82% within 2 cell doubling cycles. Cell binding to all 3 selectins (L-, E-, and P-selectin) was reduced in vitro. 4F-GalNAc was metabolically incorporated into PSGL-1, and this was accompanied by an approximately 20% reduction in PSGL-1 glycan content. A 70% to 85% reduction in HECA-452 binding epitope and N-acetyl lactosamine content in PSGL-1 was also noted on 4F-GalNAc addition. Intravenous 4F-GalNAc infusion reduced leukocyte migration to the peritoneum in a murine model of thioglycolate-induced peritonitis. Thus, the compound has pharmacologic activity. Overall, the data suggest that 4F-GalNAc may be applied as a metabolic inhibitor to reduce O-linked glycosylation, sialyl Lewis-X formation, and leukocyte adhesion via the selectins.

Total synthesis of a sialylated and sulfated oligosaccharide from O-linked glycoproteins

Abstract The total synthesis of a sialylated and sulfated oligosaccharide 1 representative of a structure occurring in respiratory mucins has been accomplished. Our strategy depends upon the employment of 2-naphthymethyl (NAP) protection for hydroxyl functions. Choice of the well-defined sialyl donor 15 was made because of its enhanced reactivity over the parent compound 14 for glycosylation.

Synthesis of precursors for the dimeric 3-O-SO3Na Lewis X and Lewis A structures.

Stereoselective syntheses of 3-O-SO3Na-beta-Gal-(1-->4)-beta-GlcNAc- (1-->3)-beta-Gal-(1-->4)-GlcNAc-beta-OBn (15) and 3-O-SO3Na-beta-Gal-(1-->3)-beta-GlcNAc-(1-->3)-beta-Gal-(1-->3)- beta-GlcNAc-(1-->3)-beta-Gal-(1-->4)-Glc-beta-OBn (25) were accomplished through the use of two novel glycosyl donors, namely, ethyl O-(2,6-di-O-acetyl-3,4-O-isopropylidene-beta-D- galactopyranosyl)-(1-->4)-3-O-acetyl-2-deoxy-2-phthalimido-1-thio-6-O- trimethylacetyl-beta-D-glucopyranoside (8). and ethyl O-(2,6-di-O-acetyl-3,4-O-isopropylidene-beta-D-galactopyranosyl)- (1-->3)-4-O-acetyl-2-deoxy-2-phthalimido-1-thio-6-O-trimethylace tyl-beta-D-glucopyranoside (18).

The binding characteristics and utilization of Aleuria aurantia, Lens culinaris and few other lectins in the elucidation of fucosyltransferase activities resembling cloned FT VI and apparently unique to colon cancer cells

Human colon carcinoma cell fucosyltransferase (FT) in contrast to the FTs of several human cancer cell lines, utilized GlcNAcbeta1,4GlcNAcbeta-O-Bn as an acceptor, the product being resistant to alpha1,6-L-Fucosidase and its formation being completely inhibited by LacNAc Type 2 acceptors. Further, this enzyme was twofold active towards the asialo agalacto glycopeptide as compared to the parent asialoglycopeptide. Only 60% of the GlcNAc moieties were released from [14C]fucosylated asialo agalacto triantennary glycopeptide by jack bean beta-N-acetylhexosaminidase. These alpha1,3-L-fucosylating activities on multiterminal GlcNAc residues and chitobiose were further examined by characterizing the products arising from fetuin triantennary and bovine IgG diantennary glycopeptides and their exoglycosidase-modified derivatives using lectin affinity chromatography. Utilization of [14C]fucosylated glycopeptides with cloned FTs indicated that Lens culinaris lectin and Aleuria aurantia lectin (AAL) required, respectively, the diantennary backbone and the chitobiose core alpha1,6-fucosyl residue for binding. The outer core alpha1,3- but not the alpha-1,2-fucosyl residues decreased the binding affinity of AAL. The AAL-binding fraction from [14C]fucosylated asialo fetuin, using colon carcinoma cell extract, contained 60% Endo F/PNGaseF resistant chains. Similarly AAL-binding species from [14C]fucosylated TFA-treated bovine IgG using colon carcinoma cell extract showed significant resistance to endo F/PNGaseF. However, no such resistance was found with the corresponding AAL non- and weak-binding species. Thus colon carcinoma cells have the capacity to fucosylate the chitobiose core in glycoproteins, and this alpha1,3-L-fucosylation is apparently responsible for the AAL binding of glycoproteins. A cloned FT VI was found to be very similar to this enzyme in acceptor substrate specificities. The colon cancer cell FT thus exhibits four catalytic roles, i.e., alpha1,3-L-fucosylation of: (a) Galbeta1,4GlcNAcbeta-; (b) multiterminal GlcNAc units in complex type chain; (c) the inner core chitobiose of glycopeptides and glycoproteins; and (d) the nonreducing terminal chiotobiose unit.

Selectin ligands: 2,3,4-tri-O-acetyl-6-O-pivaloyl-α/β-galactopyranosyl halide as novel glycosyl donor for the synthesis of 3-O-sialyl or 3-O-sulfo Lex and Lea type structures

Stereoselective syntheses of 3-O-sialyl- and 3-O-sulfo- Lewisx and Lewisa type structures are accomplished trough the use of key glycosyl donors 8 and 9.

Characterization of cancer associated mucin type O-glycans using the exchange sialylation properties of mammalian sialyltransferase ST3Gal-II

Our previous studies suggest that the α2,3sialylated T-antigen (NeuAcα2,3Galβ1,3GalNac-) and associated glycan structures are likely to be elevated during cancer. An easy and reliable strategy to label mucinous glycans that contain such carbohydrates can enable the identification of novel glycoproteins that are cancer associated. To this end, the present study demonstrates that the exchange sialylation property of mammalian ST3Gal-II can facilitate the labeling of mucin glycoproteins in cancer cells, tumor specimens, and glycoproteins in cancer sera. Results show that (i) the radiolabeled mucin glycoproteins of each of the cancer cell lines studied (T47D, MCF7, LS180, LNCaP, SKOV3, HL60, DU4475, and HepG2) is distinct either in terms of the specific glycans presented or their relative distribution. While some cell lines like T47D had only one single sialylated O-glycan, others like LS180 and DU4475 contained a complex mixture of mucinous carbohydrates. (ii) [14C]sialyl labeling of primary tumor cells identified a 25-35 kDa mucin glycoprotein unique to pancreatic tumor. Labeled glycoproteins for other cancers had higher molecular weight. (iii) Studies of [14C] sialylated human sera showed larger mucin glycopeptides and >2-fold larger mucin-type chains in human serum compared to [14C]sialyl labeled glycans of fetuin. Overall, the exchange sialylation property of ST3Gal-II provides an efficient avenue to identify mucinous proteins for applications in glycoproteomics and cancer research.

A convergent synthesis of trisaccharides with α-Neu5Ac-(2→3)-β-d-Gal-(1→4)-β-d-GlcNAc and α-Neu5Ac-(2→3)-β-d-Gal-(1→3)-α-d-GalNAc sequences

Abstract The syntheses of three trisaccharides: α-Neu5Ac-(2→3)-β- d -Gal-(1→4)-β- d -GlcNAc→OMe, α-Neu5Ac-(2→3)-β- d -Gal6SO 3 Na-(1→4)-β- d -GlcNAc→OMe, and α-Neu5Ac-(2→3)-β- d -Gal-(1→3)-α- d -GalNAc→OBn were accomplished by using either methyl (phenyl 5-acetamido-4,7,8,9-tetra- O -acetyl-3,5-dideoxy-2-thio-β- d - glycero - d - galacto -2-nonulopyranoside)onate or methyl (phenyl N -acetyl-5-acetamido-4,7,8,9-tetra- O -acetyl-3,5-dideoxy-2-thio-β- d - glycero - d - galacto -2-nonulopyranoside)onate as the sialyl donor. The N , N -diacetylamino sialyl donor appears to be more reactive than its parent acetamido sugar when allowed to react with an disaccharide acceptor under the same glycosylation conditions. The trisaccharides, as well as the intermediate products, were fully characterized by 2D DQF 1 H– 1 H COSY and 2D ROESY spectroscopy.

Synthesis of sulfo and sialyl Lewisx analogs with a mannose at the reducing end

Abstract Stereoselective syntheses of 3-O-sulfo and 3-O-sialyl LewisX analogs 1 and 2 were accomplished. Compound 1 showed greater inhibitory activity than the natural ligand sialyl LewisX against P and L-selectin.

A convenient synthesis of lacto-N-biose I [β-d-Galp-(1 → 3)-β-d-GlcpNAc] linked oligosaccharides from phenyl O-(tetra-O-acetyl-β-d-galactopyranosyl)-(1 → 3)-4,6-di-O-acetyl-2-deoxy-2-phthalimido-1-thio-β-d-glucopyranoside☆

The synthesis of two tetrasaccharides and one trisaccharide containing lacto-N-biose I (β-d-Galp-(1 → 3)-β-d-GlcpNAc) as their terminal unit was accomplished through development and utilization of a key glycosyl donor, namely, phenyl O-(2,3,4,6-tetra-O-acetyl-β-d-galactopyranosyl)-(1 → 3)-4,6-di-O-acetyl-2-deoxy-2-phthalimido-1-thio-β-d-glucopyranoside.