Gerrit H. Veeneman

Tyrosine kinase activity of purified recombinant cytoplasmic domain of platelet-derived growth factor β-receptor (β-PDGFR) and discovery of a novel inhibitor of receptor tyrosine kinases

Aberrant expression of platelet-derived growth factor and its receptor (PDGFR) has been implicated in various human disorders, including cardiovascular disease and certain types of cancer. Inhibitors of the tyrosine kinase activity of PDGFR are leads in the development of novel agents to combat these diseases. We describe here a novel, potent inhibitor of PDGFR tyrosine kinase, 3-(4-dimethylamino-benzylidenyl)-2-indolinone (DMBI). The compound also inhibits signal transduction through fibroblast growth factor receptor 1 (FGFR1), but is not active towards epidermal growth factor receptor (EGFR) or c-Src tyrosine kinase. The activity of DMBI and other tyrosine kinase inhibitors was compared in a cell-based assay as well as in an assay based on purified recombinant platelet-derived growth factor beta-receptor (beta-PDGFR) lacking the transmembrane and ligand-binding domain. We showed that this truncated beta-PDGFR could dimerize, and that dimerization was required for tyrosine kinase activity. Tyrosine kinase activity was modulated by inhibitors of beta-PDGFR autophosphorylation in cells, but not by specific inhibitors of EGFR or c-Src tyrosine kinase. We conclude that beta-PDGFR lacking the transmembrane and ligand-binding domain retains the essential properties of the full-length receptor tyrosine kinase.

Design and synthesis of a trisubstrate analogue for α(1→3)fucosyltransferase: A potential inhibitor

Phenyl 1-azido-3,4,5-tri-O-benzyl-I-deoxy-2-seleno-α-l-fuco-heptulopyranoside (5), readily accessible from perbenzylated l-fucono-1,5-lactone, is a key intermediate in the preparation of trisubstrate analogue 2. NIS mediated condensation of fucosyl donor 5 with methyl 2,4,6-tri-O-benzyl-α-d-glucopyranoside (7) and ensuing reduction of the azido function furnished ketodisaccharide 10b, which was elongated at the 1-amino group of the fucose residue with a malonic acid spacer. The thus obtained compound was deprotected and subsequently coupled with 5′-amino-5′-deoxy-guanosine to afford the target compound 2.

SYNTHESIS OF A HEXASACCHARIDE CORRESPONDING TO A PORCINE ZONA PELLUCIDA FRAGMENT THAT INHIBITS PORCINE SPERM-OOCYTE INTERACTION IN VITRO

Abstract The synthesis of hexasaccharide1, [Galβ(1-4)GlcNAc[6OSO3]β(1-3)Galβ(1-4)GlcNAcβ(1-3)Galβ(1-3)GalNAcα-O(CH2)3NH2], which corresponds to a porcine zona pellucida fragment that inhibits porcine sperm-oocyte interaction, is described. Compound1 was obtained from fully protected hexasaccharide2, which was in turn constructed from protected Galβ(1-3)GalNAc disaccharide5, containing an α-linked 3-azidopropyl spacer, and from lactosamine derivatives3 and 4. Disaccharide3 and 4 were prepared by coupling of selenophenyl glycoside6 with glycosyl acceptors containing anomeric thioethyl groups. NIS/TfOH promoted coupling of disaccharide4 with5 afforded29, which was transformed into the tetrasaccharide acceptor30 by selective removal of the levulinoyl group. Glycosylation of30 with3 afforded protected hexasaccharide2. Removal of the phthalimido groups, acetylation, followed by selective removal of the allyl group and sulphation, and finally complete deprotection afforded hexasaccharide1. The synthesis of hexasaccharide1 is described. Download : Download full-size image

Synthesis and glycosylating properties of ketopyranosyl donors

Abstract The preparation of heptulopyranosyl donors 13–15, 28, 29 and 3-octulopyranosyl donors 34, 35 , having a non-participating group at C-3 or C-4, respectively, is described. Glycosylations of various acceptors with these donors gave exclusively α-linked ketosides. On the other hand, condensation of 3-O-benzoyl heptulopyranosyl donor 19 with an acceptor furnished an anomeric mixture of ketodisaccharides.

Solution-phase and solid-phase synthesis of novel transition state inhibitors of coagulation enzymes incorporating a piperidinyl moiety

2-Amino-3-piperidin-4-yl-propionic acid containing peptidomimetics are potent protease inhibitors when combined with an appropriate keto-thiazole or keto-carboxylic acid moiety. A novel P1 residue in factor Xa and thrombin inhibitors has been found resulting in IC50 values as low as 0.048 microM, a factor of ten more potent than Argatroban. Starting with non-chiral synthetic routes, a new stereospecific route was developed as well as a new solid-phase method.

Synthesis of racemic myo-inositol 1,4,5-trismethylphosphonate, myo-inositol 4,5-bismethylphosphonate and myo-inositol 5-methylphosphonate via a phosphinate approach

Abstract Synthesis of the (rac.) myo-inositol phosphate isosteric analogues 1,4,5-trismethylphosphonate, 4,5-bismethylphosphonate, and 5-methylphosphonate was accomplished using a phosphinate approach.

Synthesis of sialic acid-lipid conjugates and their neuritogenic effects on N1E.115 neuroblastoma cells☆

Several sialic acid-lipid conjugates having one or more sialic acid residues were prepared via phosphite and methylthiomethyl intermediates. The synthetic compounds were found to promote neurite outgrowth on N1E.115 neuroblastoma cells. In particular, the trisialocholesterol derivative 19 exhibited potent neuritogenic activity.

α-Sialyl cholesterol increases laminin in Schwann cell cultures and attenuates cytostatic drug-induced reduction of laminin

Schwann cells play an important role in peripheral nerve regeneration. Here, we report the effect of alpha-sialyl cholesterol (alpha-SC), a derivative of the sialic acid-containing natural gangliosides, and the cytostatic agents, cisplatin, taxol and vincristine on the laminin production in Schwann cell cultures isolated from rat sciatic nerves. Laminin, one of several extracellular matrix components produced by Schwann cells, is known to potentiate axonal outgrowth. Laminin content was increased by alpha-SC, starting at 7.0 micrograms/ml with a maximal effect at 22.4 micrograms/ml (30%, P < 0.001). The three cytostatic drugs, dose-dependently reduced laminin content in Schwann cell cultures: (1) cisplatin at a threshold dose of 2 micrograms/ml (-26.4%, P < 0.001); (2) taxol, starting at a dose of 1 ng/ml (-8.0%, P < 0.05); and (3) vincristine, starting at 0.5 ng/ml (-5.9%, P < 0.05). Cultured Schwann cells were incubated with cytostatic drugs in combination with increasing amounts of alpha-SC and it was found that, depending on the cytostatic drug concentration used, alpha-SC could reduce or completely prevent the cytostatic drug-induced reduction of laminin in Schwann cell cultures. Co-treatment with alpha-SC also reduced part of the morphological changes caused by the cytostatic drugs. alpha-SC did not counteract the anti-proliferative effect of the cytostatic drugs on K-562 human erythroleukemia cells. In conclusion, alpha-SC increased laminin content in Schwann cell cultures and protected Schwann cell cultures against the decrease of laminin by cytostatic drugs without interfering with the anti-proliferative potential, suggesting that alpha-SC may have clinical use in protecting cancer patients against the neurotoxic effects of cytostatic drugs.