Daniel G. McCarthy

Pleiotropic role for monocyte C-fms protein in response to vascular injury: Potential therapeutic target

OBJECTIVES We examined the role of C-fms+ cells in response to vascular injury with a focus on the temporal and spatial platelet interactions, monocyte survival and proliferation within the evolving neointimal lesion and monocyte proliferation within the circulation and specified monocyte reservoir sites. Finally, we investigated the therapeutic effect of C-fms kinase inhibition (CFKI) on neointimal hyperplasia post vessel injury. METHODS AND RESULTS We utilized murine carotid-wire injury, a transgenic C-fms reporting mouse model, confocal microscopy, shear-flow studies, specific C-fms signalling inhibition to determine the activation, mobilization and recruitment of C-fms+ monocytes in the context of early and late vessel remodelling. C-fms+ cells were recruited as early as 4h and accumulated over time in the neointima following injury. Monocyte interaction with platelet thrombus under flow and in vivo, in addition to monocyte mobilisation into the circulation post-injury was impaired by CFKI administration. Sustained inhibition of C-fms over 1-2 weeks abrogated the neointimal response but preserved re-endothelialisation post-injury. CONCLUSION These data establish C-fms as a key regulator of the vascular response to injury and a potentially attractive therapeutic target in disease states where neointimal hyperplasia, monocyte activation and pathologic remodelling are prominent and endothelial homeostasis is desirable.

THE PECULIAR α-AMIDOALKYLATION OF VINYLTRIMETHYLSILANE

Abstract α-Amidoalkylation of allyttrimethylsilane with methyl-2-chloro-2-(p-chlorobenzoylamino)-ethanoate 1 gave in the presence of Lewis acid racemic methyl-2- (p-chlorobenzoylamino)-4-penteno ate 2. Under the same conditions, vinlytrimethylsilane afforded (±)-trans-2-(p-chlorophenyl)-5,6-dihydro-4-methoxycarbonyl-6-trimethylsilyl-4H-1, 3-oxazine 4 as the major, by n.m.r. data and x-ray crystallography established product.

Dehydration of formamides using the Burgess Reagent: a new route to isocyanides

The Burgess Reagent readily converts formamides into isocyanides in high yields and is particularly effective for substrates containing halide sensitive trimethylsilyl ether groups.

Rapid acid-catalysed and uncatalysed hydration of ketenimines

The rates of hydration of a series of ketenimines (9) have been examined in water (µ 1.0; 25°) over the pH range 2–13. Three mechanisms of hydration to the amides (8) were noted: (a) general acid catalysis by proton transfer from H3O+ in the pH range 2–7 (giving kH3O+/kD3O+ 2.65); (b) general acid catalysis by H2O at pH > 7 (where kH2O+/kD2O+= 4.8); (c) rate-determining HO– attack. The last mechanism was only shown by N-arylketenimines, e.g.(9e); other N-alkylketenimines continue to react by rate-determining proton transfer from water even at pH 13. This result is confirmed by the incorporation of just one deuterium when (9a) reacted in acidic or basic D2O, while the deuteriated ketenimine (9f) does not loose the label on reaction in water. Substituent effects are parallel for reactions involving H+ transfer from H3O+ or H2O; the major effects are obtained on changing substituents at carbon (the protonation site). For example, replacement of C–H by C–Me reduces the reactivity by 10–20-fold, while replacement of C–Me by C–Ph reduces the rate of hydration by > 100-fold. Ammonium ions also generally react with ketenimines by rate-determining H+ transfer to the ketenimine followed by trapping of the nitrilium ion formed by the free amine. Only with the strongest amine base studied (piperidine) does direct nucleophilic attack on the ketenimine compete.

Acylation of O-alkylbenzohydroxamic acids; configurational assignment, interconversion, and rearrangement of the E- and Z-isomers of a new group of O-acyl isoamides

Acylation of the silver salts of O-alkylbenzohydroxamic acids (1) gives Z-acetic benzoalkoximic anhydrides (3) which do not rearrange to the isomeric N-acyl-N-benzoyl-O-alkylhydroxylamines (5) on heating. U.v. irradiation of the Z-isomers (3) in hexane or benzene induces a photostationary equilibrium of the E- and Z-isomers (4) and (3), which were separated by chromatographic, methods. On heating at reflux for 30 min in carbon tetrachloride the E-isomers (4) rearrange to (5). by an O → N [1,3] acyl migration. The 1H n.m.r. chemical shifts and the u.v. extinction coefficients for isomers (3) and (4) were found to vary in the same relative way in the six pairs of compounds examined. Diazotization of O-(n-propyl)benzamidoxime in acetic acid yields only the Z-isomer (3), possibly via stereospecific reaction of acetate with an intermediate N-alkoxynitrilium ion (13). Consistent with this is the observation that only the Z-O-alkylbenzohydroximoyl chloride (9a) is formed on reaction of (13) with Cl– under similar conditions.

N-hydroxy-compounds as acyl transfer agents. Part 1. Kinetics and mechanism of nucleophilic displacements on 1-hydroxybenzotriazole esters and crystal and molecular structure of 1-benzoyloxybenzotriazole

1-Hydroxybenzotriazole esters (3) show surprisingly rapid acyl transfer to HO–, H2O, and to primary amines; the reactions are ca. 103-fold faster than with p-nitrophenyl esters where the leaving group has a similar pKa. The acylating ability of (3) is therefore akin to that of anhydrides or N-acylimidazoles. No evidence however was found to indicate that the esters exist in the N-acyl form (9) or (10) and an X-ray crystallographic study on (3; X = H, R = Ph) shows the O-acyl structure : in solution this ester retains the spectral characteristics of the solid. The ρ value for HO– attack on (3; X = H), is + 1.83 while electron-withdrawing substituents in the hydroxybenzotriazole leaving group also enhance the reactivity of the ester (ruling out a nitrenium ion mechanism). For aminolysis βNuc= 0.80 (primary amines) and 0.92 (α-effect amities). For water attack on (3; R = Ar), the Hammett ρ=+ 1.39, while kH2O/kD2O= 2.2 and general base catalysis by acetate ion and by tertiary amines (where β= 0.46) is observed. Carbonate esters (3; R = PhO) show similar enhanced reactivity as do N-protected amino-acid esters (3; R = CH2NHCO2CH2Ph or CH2NHCOPh); the i.r. spectrum of the N-benzoyloxycarbonylglycine ester is unusual however in that no carbonyl absorptions >1 800 cm–1 were observed in the solid or solutions.

Lewis acid mediated elimination and rearrangement reactions of α-chlorosulfides derived from phenylthio-substituted 4,5-dihydrofuran-3(2H)-ones.

Phenylthio-substituted 4,5-dihydrofuran-3(2H)-ones were converted into α-chlorosulfides in a highly diastereoselective manner with sulfuryl chloride. Treatment of the chlorides with stoichiometric amounts of Lewis acids gave furan-3(2H)-one products resulting from elimination and aryl group migrations. Similar behaviour was observed with an α-acetoxy sulfide derivative. The X-ray crystal structures of a representative α-chlorosulfide and of a novel, ring sulfenylated product were determined.

Reactions of ketenimines with arene-sulfanyl and -selanyl chlorides: a general route to secondary amide derivatives and a new synthesis of C-sulfanyl- and C-selanyl-ketenimines

Ketenimines 1, react with arene-sulfanyl and -selanyl chlorides to give the imidoyl chlorides 3 that either yield the substituted amides 4 upon solvolysis in aqueous acetone, or the C-sulfanyl- and C-selanyl-ketenimines 5 by dehydrochlorination with triethylamine.

Isomerisation of (E)-O-acyl isoamides to N-acyl amides. Mechanism of an intramolecular [1,3] acyl group migration via a four-membered transition state

The (Z)-O-acyl isoamides (7)(which do not themselves thermally rearrange) may be photoisomerised to the (E)isomers (8) which undergo a ready thermal rearrangement to the more stable N-acyl isomers (9). The mechanism of this rearrangement was investigated using solvent effects (a linear free energy correlation with dielectric constant was observed but with an overall low sensitivity to solvent) and substituent effects in the migrating aroyl group (8; R2= Ar)(ρ+ 0.65) and the aryl group attached to carbon (ρ–0.49) and to nitrogen (ρ–0.91). The mechanisms discussed include a sigmatropic π2s+σ2a pathway, but that favoured is rate-determining nucleophilic attack by the nitrogen lone pair on the carbonyl carbon with an early transition state. Intermolecular acylation of water by (7) and (8)(which is acid and base catalysed) and of piperidine were examined as analogues of the intramolecular process. In general, the rates of intermolecular reactions of the (Z)-and (E)-O-acyl isoamide isomers (7) and (8) are similar to one another and show the same sensitivity to substituent effects.

CYCLISATIONS OF BENZENESULFENYL CHLORIDE ADDUCTS WITH CONJUGATED SILYLOXYENONES : A NEW STEREOSELECTIVE REACTION IN THE SYNTHESIS OF 4,5-DIHYDROFURAN- 3(2H)-ONES

Adducts, generated in situ from E-α′-trialkylsilyloxy-α,β -unsaturated ketones with benzenesulfenyl chloride, cyclise in the presence of dry silica or zinc bromide to produce phenylsulfanyl substituted 4,5-dihydrofuran-3(2H)-ones with high stereoselectivity; oxidative elimination of the phenylsulfanyl group completes a new route to furan-3(2H)-ones.