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C Laplante

Publications and source records attributed to C Laplante.

9 recordsLinked to original sources
PubMed2001

Direct mono-N-methylation of solid-supported amino acids: a useful application of the Matteson rearrangement of alpha-aminoalkylboronic esters.

[reaction: see text] A novel solid-phase method for the mono-N-methylation of resin-supported amino acids was developed on the basis of Matteson's 1,2-carbon-to-nitrogen migration of boron in alpha-aminoalkylboronic esters. Amino acids supported on either Wang resin or the highly acid-sensitive SASRIN resin can be methylated by reaction with pinacol chloromethylboronic ester, followed by rearrangement of the resulting aminomethylboronate and subsequent cleavage of the boronate group. This direct method requires only a simple and expedient oxidative resin wash to repair overalkylated sites.

Amino Acids↗
PubMed2001

A mild and general solid-phase method for the synthesis of chiral polyamines. Solution studies on the cleavage of borane-amine intermediates from the reduction of secondary amides.

A mild oxidative workup protocol using iodine in an acetic acid-acetate buffer solution is described for the cleavage of borane-amine adducts arising from the borane-promoted reduction of polyamides supported onto practical trityl-based resins. Chiral polyamines with diverse side-chain functionalities can be generated as free bases without premature release from the solid support and with essentially no racemization using this method. A series of model oligomeric secondary diamides 6 containing various alpha-amino acid residues (Val, Phe, Tyr, Ser, Cys, Met, Gln, Trp) provided triamine products 8 in high yields and good to excellent purity. On the other hand, a substrate containing a tertiary amide (15) formed a rather unusual triaminoborane intermediate that required more stringent workup conditions to liberate the polyamine product 20. The reduction of oligomeric tertiary amides such as 9 was found sluggish, but these compounds could nonetheless be obtained in high purity from in situ reductive amination of the corresponding secondary amines. Control studies, carried out in solution with model secondary amide 23, confirmed the efficiency of the buffered iodine solution and highlighted several advantages (no heating necessary, no need for strong bases or acids) over existing methods for the cleavage of borane-amine adducts. A possible mechanism involving all buffer components (iodine, acetic acid, and acetate ion) is proposed in which borane-amine adducts are transformed first to the monoiodoborane-amine and then to the corresponding acetoxyborane-amine adduct of much weaker coordination affinity. The latter would dissociate readily and get trapped by the acetic acid to provide the desired secondary amine. This reduction/oxidative workup protocol is useful as a general method for the facile solid-phase synthesis of polyamines for eventual release in solution and use in various applications. It is also potentially very useful toward the synthesis and screening of bead-supported libraries of free oligoamines assembled through split-pool methods.

Journal Article↗
PubMed1993

Effects of EGF, IL-1 and their combination on in vitro corneal epithelial wound closure and cell chemotaxis.

We investigated the effects of EGF, IL-1 and their combination on closure of wounds inflicted on rabbit corneal epithelial cell cultures and on migration of these cells in microchemotaxis chambers. In vitro corneal epithelial wound closure depended on the applied concentrations of EGF or IL-1. Twenty-four hours after wounding, the smallest wounds were obtained with 50 ng ml-1 of EGF and 1 ng ml-1 of IL-1, respectively. The effect on wound closure of combinations of EGF and IL-1 was additive even at concentrations that were optimal for each growth factor when applied alone. We found that EGF increases the chemotactic migration of rabbit corneal epithelial cells. Cell chemotaxis depended both on the concentration of EGF and on the number of cells applied in the assay. This response to EGF was seen at concentrations that were effective in the wound closure assay. The magnitude of the chemotactic migration response was much smaller with IL-1 than with EGF. Similarly to the observations on wound closure, the effect on cell chemotaxis of combinations of EGF and IL-1 was additive. The ability of EGF, and EGF/IL-1 combinations to modulate corneal epithelial cell chemotactic migration supports migration as a possible biological mechanism of the acceleration of corneal epithelium wound closure by these drugs.

Animals↗
PubMed1990

Contractile effect of the chemotactic factors f-Met-Leu-Phe and C5a on the human isolated umbilical artery. Role of cyclooxygenase products and tissue macrophages.

Factors that are chemotactic for phagocytic leukocytes are known to elicit important acute circulatory changes, and the role of circulating leukocytes in these models is controversial. To evaluate the role of the blood vessel wall in the absence of circulating cells, spiral strips of human umbilical artery were exposed in vitro to the chemotactic peptides f-Met-Leu-Phe (1-100 nM) or C5a (2.5-25 nM). Contractile responses were observed for both peptides. Certain agonist analogues and a selective antagonist of the chemotactic action of f-Met-Leu-Phe behaved correspondingly as agonists and antagonist of the contractile effect on umbilical artery. The anaphylatoxin C3a also exerted a contractile effect on the tissue (25 nM and above), but this effect was highly tachyphylactic. Inhibitory drugs were used to examine the contributions of secondary mediators in eliciting the effects of C5a and f-Met-Leu-Phe. The contractile effect of both peptides was massively inhibited either by indomethacin or the thromboxane A2/prostaglandin H2 antagonist SQ 29548. Dazmegrel, a thromboxane A2 synthetase inhibitor, had partial inhibitory effects on contractions induced by either peptide. The contractile effect of C3a was prevented by indomethacin pretreatment. Vascular strips did not release measurable histamine in the bathing fluid after challenge with C5a or f-Met-Leu-Phe. The tissue apparently contains neither histamine nor mast cells. Autoradiography of 125I-labeled C5a or f-Met-Leu-Phe analogue showed specific binding of the peptides to cells dispersed in the vessel wall, but more frequently at the periphery. Cells stained positively for alpha-naphthyl acetate esterase showed a similar distribution. Pure cultures of smooth muscle cells derived from the umbilical artery failed to release prostanoids when exposed to f-Met-Leu-Phe or C5a, whereas fresh strips of this artery released more thromboxane B2 than the baseline in response to these peptides. We conclude that macrophagelike cells, present in the vessel wall, are the likely target cells for the chemotactic peptides. These cells trigger a contractile effect of the smooth muscle by generating cyclooxygenase products.

Anaphylatoxins↗
PubMed1990

Interactions between alveolar macrophage subpopulations modulate their migratory function.

To better understand the mechanisms by which alveolar macrophages (AM) are attracted to local sites in the lung, the locomotion of AM in response to N-formyl-methionyl-leucyl-phenylalanine (FMLP) was investigated. Total bronchoalveolar cells (99% AM) obtained by a nondiscriminating bronchoalveolar lavage procedure migrated toward FMLP over a range of concentrations of 10(-12) M to 10(-6) M. Dose-response experiments showed a biphasic response with two peaks of migration obtained respectively at 5 x 10(-10) M and 10(-8) M. Analysis in the presence and absence of a positive gradient of FMLP revealed that the first peak of migration (5 x 10(-10) M FMLP) corresponded predominantly to chemotactic activity whereas the second peak of migration (10(-8) M FMLP) was associated with chemokinetic activity. To further evaluate these activities of oriented (chemotaxis) vs. random (chemokinesis) migration, AM were separated into two fractions by a two-step bronchoalveolar lavage procedure. Whereas fraction 1 displayed exclusively chemokinesis in response to higher concentrations of FMLP (10(-8) M), fraction 2 was totally unresponsive to FMLP over a wide range of concentrations (5 x 10(-11) M - 10(-7) M). When both fractions were combined, however, the chemotactic response to low concentrations of FMLP (5 x 10(-10) M) was restored. Additional analysis of these two AM fractions indicated that fraction 1 AM had a significantly lower degree of adherence and aggregation than fraction 2 AM. These data suggest that cell-cell cooperation is important for AM chemotactic response to FMLP and that such interaction may involve changes in adherence and aggregation.

Animals↗
PubMed1989

Relaxant effect of N-formyl-methionyl-leucyl-phenylalanine on rabbit vascular strips.

Some types of rabbit isolated blood vessels precontracted with phenylephrine relaxed when exposed to the chemotactic peptide N-formyl-Met-Leu-Phe (FMLP). The thoracic aorta was unresponsive whereas the portal vein and pulmonary artery exhibited concentration-dependent relaxing responses to FMLP (1-100 nM). FMLP-induced relaxations developed over several minutes and occurred after a latency of 30 to 40 sec. An inconsistent, brief and small contractile phase preceded the relaxations in some tissues. Stable responses to FMLP could be obtained repeatedly at 1.5-hr intervals. On both the portal vein and the pulmonary artery, the structure-activity relationship of peptides related to FMLP was similar to the one reported for activating phagocytic leukocytes. The peptide Boc-Phe-D-Leu-Phe-D-Leu-Phe behaved as a competitive antagonist of FMLP-induced relaxations with a calculated pA2 of 7.5 on both types of responsive vessels. Indomethacin inhibited the relaxations completely on the pulmonary artery and partially on the portal vein. FMLP-induced vasorelaxations were unaffected by a platelet-activating factor antagonist, BN 52021, or a 5-lipoxygenase inhibitor, L-651,392. Removal of the endothelium did not prevent the relaxant response to FMLP. The release of 6-keto-prostaglandin F1 alpha in the bathing fluid of portal vein and pulmonary artery exposed to FMLP was demonstrated using a radioimmunoassay. FMLP relaxed rabbit vascular strips in a blood-free environment by releasing secondary mediators tentatively identified as prostaglandins; however, a component of the relaxation in the portal vein was not mediated by cyclooxygenase products.

6-Ketoprostaglandin F1 alpha↗
PubMed1988

Structural and functional analysis of poly(ADP ribose) polymerase: an immunological study.

Poly(ADP ribose) polymerase (EC 2.4.2.30) was studied using monoclonal antibodies for three different epitopes on the enzyme. The epitopes were mapped in relation to the functional domains of the protein and the inhibitory properties of the antibodies. The intranuclear and interspecies immunoreactivity of the enzyme was also investigated. The epitope of antibody 2 was mapped to the 17 kDa fragment generated by chymotryptic digestion of the C-terminal 54 kDa NAD-binding domain. Antibody 9 binds to the N-terminal 29 kDa fragment of the DNA binding domain and inhibits the enzyme activity by 80%. This antibody was used to purify poly(ADP ribose) polymerase by immunoaffinity chromatography. The third antibody binds to a central 36 kDa fragment that possesses part of the DNA-binding domain and the automodification domain. This antibody increases the enzymatic activity by 30%. An analysis of the species cross-reactivity of the antibodies was carried out by immunoblot analysis of nuclear proteins. Antibody 10 binding was detected in rat FR3T3 cells, Chinese hamster ovary cells (CHO) and epidermoid carcinoma lung human cells (CALU-1). The other two antibodies are specific for the human and bovine enzymes. Western blot analysis showed the association of poly(ADP ribose) polymerase with residual nuclear material obtained after nuclease treatment and high-salt extraction. Immunofluorescence studies with the three different monoclonals demonstrated that accessibility of the epitopes varies in the nucleus.

Animals↗
PubMed1988

Small fibronectin fragments induce endothelium-dependent vascular relaxations.

Strips of rabbit thoracic aorta precontracted with phenylephrine relaxed when exposed to selected synthetic peptides derived from the cell attachment domain of fibronectin. The relaxations elicited by both acetylcholine and the hexapeptide Gly-Arg-Gly-Asp-Ser-Pro (GRGDSP) were dependent on the presence of an intact endothelium, were resistant to indomethacin, and were inhibited by hemoglobin. The structure-activity relationship of four oligopeptides derived from fibronectin was in fair agreement with their ability to prevent fibronectin-mediated cell adhesion in other experimental systems. Human plasma fibronectin (up to 2.3 microM) did not relax this preparation and did not prevent the relaxant effect of the synthetic hexapeptide GRGDSP. On the rabbit isolated mesenteric artery, the relaxations induced by GRGDSP were significantly inhibited by indomethacin treatment, suggesting a contribution of locally produced prostaglandins. The displacement of fibronectin by soluble peptides from its binding sites on endothelial cells may result in significant pharmacologic responses, probably resulting from perturbations of the endothelial cell membranes.

Acetylcholine↗