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A core 4,5,6,7-tetrahydroisoxazolo[4,3-c]pyridine-4-one scaffold is elaborated at C-3(Me) by base-mediated aldol condensation to give new 3-alkenyl-4,5,6,7-tetrahydroisoxazolo[4,3-c]pyridine-4-ones, which are masked forms related to the acylpyridone natural products.

O -Alkyl and O -aryl carbamate derivatives of the antimalarial drug primaquine were synthesised as potential prodrugs that prevent oxidative deamination to the inactive metabolite carboxyprimaquine. Both O -alkyl and O -aryl carbamates undergo hydrolysis in alkaline and pH 7.4 phosphate buffers to the parent drug, with O -aryl carbamates being ca. 10 6 –10 10 more reactive than their O -alkyl counterparts. In human plasma O -alkyl carbamates were stable, whereas in contrast their O -aryl counterparts rapidly released the corresponding phenol product, with primaquine being released only slowly over longer incubation periods. Activation of the O -aryl carbamates in human plasma appears to be catalysed by butyrylcholinesterase (BuChE), which leads to carbamoylation of the catalytic serine of the enzyme followed by subsequent slow enzyme reactivation and release of parent drug. Most of the O -aryl and O -alkyl carbamates are activated in rat liver homogenates with half-lives ranging from 9 to 15 h, while the 4-nitrophenyl carbamate was hydrolysed too rapidly to determine an accurate rate constant. Antimalarial activity was studied using a model consisting of Plasmodium berghei , Balb C mice and Anopheles stephensi mosquitoes. When compared to controls, ethyl and n -hexyl carbamates were able to significantly reduce the percentage of infected mosquitos as well as the mean number of oocysts per infected mosquito, thus indicating that O -alkyl carbamates of primaquine have the potential to be developed as transmission-blocking antimalarial agents.

The reactivity of 6-quinolinyl and 8-quinolinyl N,N-dimethylcarbamates was examined in several aqueous basic media. A quadratic dependence was observed for the constant rates upon hydroxide concentration for both compounds, which is a typical behaviour of a mechanism involving a base-catalysed deprotonation of the tetrahedral intermediate with the formation of a dianion at high concentrations of hydroxide ion, while at lower concentrations a specific-base catalysed addition–elimination mechanism seems to be predominant. The reactivity of 8-quinolinyl N,N-dimethylcarbamate was also studied in several amine buffers, showing specific base catalysis. The reactivity of 6-quinolinyl N,N-dimethylcarbamate was studied in H2O and in D2O and the solvent isotope effect supports the proposal of a mechanism involving a specific-base hydrolysis. All results confirm the existence of a mechanism with a rate determining step involving the substrate anion and a second mole of hydroxide ion. This mechanism was so far unknown for carbamate reactivity, being only known to occur with amides. Copyright © 2011 John Wiley & Sons, Ltd.

S-Alkylation of an N-protected cysteine ester with a range of ω-iodoalkyl heterocycles affords 11 novel non-proteinogenic heterocyclic amino acids having a sulfur atom in the backboneheterocycle linker.

The 4-oxo-β-lactams (azetidine-2,4-diones) are potent acylating agents of the human leukocyte elastase (HLE), a neutrophil serine protease that plays a key role in several inflammatory diseases. A novel 4-oxo-β-lactam containing a N-(4-(phenylsulphonylmethyl)phenyl) group, 3, was designed as a potential mechanism-based inhibitor capable of undergoing elimination of phenylsulphinate upon Ser-195 acylation. Compound 3 was found to be a potent slow-tight binding inhibitor of HLE, presenting a remarkable second-order rate constant of 1.46 x 10⁶ M⁻¹s⁻¹ and displaying selectivity over the proteinase 3 and cathepsin G. However, liberation of phenylsulphinate was not observed in the hydrolysis of 3 in both pH 7.4 phosphate buffer and human plasma. The C(max) values of 1207 μg/total blood, 179 μg/g spleen and 106 μg/g lung were determined by HPLC, following a single 30 mg/kg dose of 3 given intraperitoneally to NMRI mice, suggesting that the inhibitor distributes well into tissues. Although being a powerful selective inhibitor of HLE, 4-oxo-β-lactam 3 has a limited stability, being susceptible to off-target reactions (plasma and liver enzymes).

It is generally recognized that insect odorant binding proteins (OBPs) mediate the solubilisation and transport of hydrophobic odorant molecules and contribute to the sensitivity of the insect olfactory system. However, the exact mechanism by which OBPs deliver odorants to olfactory receptors and their role, if any, as selectivity filters for specific odorants, are still a matter of debate. In the case of Anopheles gambiae recent studies indicate that ligand discrimination is effected through the formation of heterodimers such as AgamOBP1 and AgamOBP4 (odorant binding proteins 1 and 4 from Anopheles gambiae). Furthermore, AgamOBPs have been reported to be promiscuous in binding more than one ligand simultaneously and repellents such as DEET (N,N-diethyl-3-toluamide) and 6-MH (6-methyl-5-hepten-2-one) interact directly with mosquito OBPs and/or compete for the binding of attractive odorants thus disrupting OBP heterodimerisation. In this paper, we propose mechanisms of action of DEET and 6-MH. We also predict that ligand binding can occur in several locations of AgamOBP1 with partial occupancies and propose structural features appropriate for repellent pharmacophores.

A core isoxazolo[4,3-c]pyridin-4-one scaffold is prepared and elaborated at C-3(Me) and C-7 as a masked building block for 3-acylpyridin-2-ones related to the acylpyridone natural products.

Dipolar cycloadditions of azomethine imines, formed in situ from aldehydes and N1-alkyl-N2-acylhydrazines, with electron-deficient dipolarophiles produce pyrazolidines: mono-substituted dipolarophiles afford principally 4-substituted pyrazolidines.

Substituted secondary N-thiazolylcarbamate esters and some tertiary N-methyl, N-thiazolyl carbamate esters have been synthesised and the mechanism of the OH- catalysed hydrolyses investigated. These proved to be E1cB and BAc2 respectively, and this behaviour was compared with that of other carbamates.

Carbamate and ester derivatives of the 1,1-dioxobenzo[b]thiophen-2-ylmethyloxycarbonyl (Bsmoc) scaffold react readily with thiols via a Michael addition at rates not significantly affected by the nature of the carboxylic or carbamic acid leaving group. These Michael acceptors are irreversible inhibitors of the cysteine proteases papain and human liver cathepsin B, displaying first-order kinetics with respect to inhibitor concentration. In contrast, none of the Bsmoc derivatives inhibited porcine pancreatic elastase, a serine protease. (C) 2006 Elsevier Ltd. All rights reserved.

Human leukocyte elastase (HLE) is a serine protease that very efficiently degrades various tissue matrix proteins such as elastin. The imbalance between HLE and its endogenous inhibitors leads to excessive elastin proteolysis and is considered to be responsible for the onset of chronic obstructive pulmonary disease (COPD). A novel series of C-3-, C-4-, and N-1-substituted azetidin-2-ones were prepared as potential mechanism-based inhibitors of HLE to restore the protease/antiprotease imbalance. N-Acyloxyalkylazetidin-2-ones, 4, and their carbamate counterparts, 5, are weak HLE inhibitors, being 5 times less active than their bicyclic oxazolidin-2,4-dione-substituted analogues, 6, containing an electron-withdrawing substituent at C-4. Compounds 6 containing a C-4 substituent exist as two diastereomeric pairs of enantiomers, each pair presenting similar inhibitory activity against HLE. Comparative docking experiments with the C-4-substituted oxazolidin-2,4-dione inhibitors 6 suggest that only the 4R,5‘S and...

Novel N-Mannich base-type derivatives of the antimalarial drug amodiaquine were synthesised by reaction with tertiary N-chloromethylamides. With the exception of the derivative of ethyl hippurate, all the so-formed (1-amidomethyl-1H-quinolin-4-ylidene)arylamines displayed high chemical and enzymatic stability. These compounds displayed antimalarial activity against the multi-drug resistant Plasmodium falciparum strain Dd2 (IC50 values 15–31 nM) and demonstrated no significant loss in activity compared to amodiaquine (IC50 30 nM).

The synthesis of imidazolidin-4-one derivatives of primaquine as potential antimalarial agents is described. The target compounds were synthesized in three steps: (i) condensation of (±)-primaquine with N α -protected amino acids, (ii) removal of the N α -protecting group, and (iii) reaction of the N-acylprimaquine with a carbonyl compound: acetone, three cyclic ketones and veratraldehyde. Using 2-formylbenzoic acid in the third step afforded 1 H -imidazo[2,1- a ]isoindole-2,5(3 H ,9b H )-diones. All products were isolated in good to excellent yields. Whereas imidazolidin-4-ones were formed as mixtures of all possible diastereomers in equal amounts, 1 H -imidazo[2,1- a ]isoindole-2,5(3 H ,9b H )-diones were produced in a stereoselective fashion. The compounds hydrolyse very slowly ( t 1/2 5–30 d) in pH 7.4 buffer to release primaquine. These primaquine derivatives are being submitted to biological assays, and preliminary results of their antimalarial activity are quite encouraging.

Tertiary benzamides are oxidized by the 5,10,15,20-tetraphenylporphyrinatoiron(III) chloride-(BuOOH)-O-t system at the alpha-position of the N-alkyl groups. The major products are N-acylamides, although small amounts of secondary amides, the products of dealkylation, are also formed. Plots of initial rate versus initial substrate concentration for these reactions are curved, suggesting formation of an oxidant-substrate complex. The reaction rates are almost insensitive to the substituent in the benzamide moiety, but there is a kinetic deuterium isotope effect of 5.6 for the reaction of the N, N-(CH3)(2) and N, N-(CD3)(2) compounds. Comparison of the reaction products from N-alkyl-N-methylbenzamides reveals that, for all compounds studied except N-cyclopropyl-N-methylbenzamide, oxidation of the alkyl group is preferred, strongly so (by a factor of ca. 8) for N-allyl-N-methylbenzamide. In contrast to microsomal oxidation, there is no steric hindrance to oxidation of an isopropyl group. Thus, we propose that these reactions proceed via hydrogen atom abstraction to form an alpha-carbon-centred radical and we attribute the observed diminished reactivity of the N-cyclopropyl group to its known reluctance to form a cyclopropyl radical. Oxidation of N-methyl-N-(2,2,3,3-tetramethylcyclopropyl)methylbenzamide provides preliminary evidence for rearrangement of an intermediate radical. While it remains unclear how these reactions proceed directly to the N-acyl products, we have established that N- hydroxymethyl, N-alkoxymethyl and N-alkylperoxymethyl intermediates are not involved.

Aminocarbonyloxymethyl esters 3 based on (S)-amino acid carriers were synthesised and evaluated as potential prodrugs of carboxylic acid agents. In addition, the compounds were evaluated as topical prodrugs with the aim of improving the dermal delivery of two non-steroidal anti-inflammatory agents: naproxen and flufenamic acid. The lipophilicities of these compounds were determined and their hydrolyses in aqueous solutions and in human plasma were examined. Compounds 3 containing a secondary carbamate group were hydrolysed at pH 7.4 by two different routes: (i) direct nucleophilic attack at the ester carbonyl carbon leading to the release of the parent carboxylic acid and (ii) intramolecular rearrangement involving an O--N acyl migration, leading to the formation of the corresponding amide. The rearrangement pathway is highly dependent on the size of the carboxylic acid and amino acid substituents, being eliminated when the amino acid is valine or leucine. In contrast, compounds 3 decomposed in plasma exclusively through ester hydrolysis, most releasing the parent carboxylic acid quantitatively with half-lives shorter than 5 min. The permeation of selected prodrugs across excised postmortem human skin was studied in vitro. All prodrugs evaluated exhibited a lower flux than the corresponding parent carboxylic acid. The poor skin permeation observed for compounds 3 is most probably due to their low aqueous solubility and high partition coefficient. (C) 2002 Elsevier Science Ltd. All rights reserved.

N -(2-iodoethyl) and N -(3-iodopropyl)pyrimidines and purines undergo stereoselective conjugate radical addition with an optically active oxazolidinone acceptor to give syn -adducts that can be converted into amino acids carrying pyrimidine and purine (nucleobase) side chains.

4,5-Dihydroimidazoles undergo an N-alkylation and 1,3-dipolar cycloaddition cascade with unsaturated α-bromoketones, with subsequent eliminative ring-opening, recyclisation and tautomerisation to form unexpected hexahydropyrrolo[1,2,3-de]quinoxalines.

The kinetics of the hydrolyses of secondary and tertiary N-amidomethylsulfonamides were studied at 50 degreesC. Both types of N-amidomethylsulfonamide hydrolyse through acid- and base-catalysed processes, as indicated by the pH-rate profiles. The order of reactivity for the acid-catalysed pathway implies a mechanism involving protonation of the amide followed by expulsion of a neutral amide and formation of a sulfonyliminium ion. In the base-catalysed region, compound 5c, which is substituted at both amide and sulfonamide nitrogen atoms, hydrolyses by nucleophilic attack of hydroxide ion at the amide carbonyl carbon atom to form benzoic acid and a sulfonamide. In contrast, compound 5b, which contains a sulfonamide NH group, hydrolyses to benzamide and sulfonamide products by an E1cb(rev) mechanism involving ionisation of the sulfonamide. Compound 5a, which contains an amide NH, also hydrolyses to sulfonamide and amide products, probably by an E2 mechanism.

An orthogonally protected 3-(1-aminoalkyl)isoxazole-4-carboxylic acid has been prepared by 1,3-dipolar cycloaddition of a suitably protected α-aminonitrile oxide with an enaminoester dipolarophile; this protected amino acid has been deprotected and coupled independently at either the C- or N-terminus to produce pseudopeptide segments as peptide mimetics that contain a cis -amide bond replacement.

A series of 3-acyloxymethyloxycarbonyl-1-aryl-3-methyltriazenes 5 was synthesised by the sequential reaction of 1-aryl-3-methyltriazenes with (i) chloromethyl chloroformate, (ii) NaI in dry acetone, and (iii) either the silver carboxylate or the carboxylic acids in the presence of silver carbonate. The hydrolysis of these compounds was studied in pH 7.7 isotonic phosphate buffer and in human plasma. Triazene acyloxycarbamates demonstrated their ability to act as substrates for plasma enzymes. For compound 5f, a pH-rate profile was obtained which showed the hydrolysis to involve acid-base catalysis. The reaction is also buffer catalysed. Thus, at pH 7.7, pH-independent, base-catalysed and buffer-catalysed processes all contribute to the hydrolysis reaction. The sensitivity of the hydrolysis reaction to various structural parameters in the substrates indicates that hydrolysis occurs at the ester rather than the carbamate functionality. In plasma, the rates of hydrolysis correlate with partition coefficients, the most lipophilic compounds being the most stable. An aspirin derivative suffers two consecutive enzymatic reactions, the scission of the aspirin acetyl group being followed by the scission of the acyloxy ester group. These results indicate that triazene acyloxymethyl carbamates are prodrugs of the antitumour monomethyltriazenes. They combine chemical stability with a rapid enzymatic hydrolysis, and are consequently good candidates for further prodrug development. Moreover, this type of derivative allowed the synthesis of mutual prodrugs, associating the antitumour monomethyltriazenes with anti-inflammatory NSAIDs as well as with the anticancer agent butyric acid.

Tertiary sulfonamidomethyl esters of benzylpenicillin ( 4 ) were synthesised and evaluated as a new class of potential prodrugs for β-lactam antibiotics. Their hydrolysis in aqueous buffers was studied by HPLC and reveal a U-shaped pH–rate profile with a pH-independent process extending from ca. pH 2 to ca. pH 10. This pathway is characterised by kinetic data that are consistent with a unimolecular mechanism involving rate-limiting iminium ion formation and penicillinoate expulsion. Benzylpenicillin and the corresponding sulfonamide are the ultimate products detected and isolated, indicating that β-lactam ring opening is much slower than ester hydrolysis. As expected from the high reactivity, benzylpenicillin esters ( 4 ) displayed similar in vitro antibacterial activity to benzylpenicillin itself. Compared to the benzylpenicillin derivatives, sulfonamidomethyl esters of benzoic, clofibric and valproic acids display a much higher stability, giving rise to a Bronsted β lg value of −0.96 and suggesting that tertiary sulfonamidomethyl esters may be useful prodrugs for carboxylic acid drugs with p K a >4.

N-(But-3-enyl)-N-methylbenzamide 14a undergoes microsomal oxidation by rat liver microsomes to yield both N-methyl- and N-(but-3-enyl)benzamides 18a and 19, the products of N-dealkylation. Cyclic products, that could be derived from a carbon-centred radical formed by hydrogen atom abstraction from the N-methyl group, were not observed. When generated independently, this carbon-centred radical underwent cyclisation, the 5-exo-trig mode being preferred to 6-endo-trig by a factor of 5. In contrast, N-(but-3-ynyl)-N-methylbenzamide 15 undergoes microsomal oxidation to yield the products of dealkylation 18a and 23 and also N-benzoylpiperidone 24. Dealkylation is preferred by factor of 3 and the piperidone accounts for ca. 45% of the reaction at the N-methyl group. Piperidone formation is consistent with the generation of a carbon-centred radical α- to the amide nitrogen atom during dealkylation and implies that cyclisation proceeds preferentially via the 6-endo-dig mode. Generated independently the radical undergoes cyclisation by both 5-exo-dig and 6-endo-dig modes, the former being favoured by a factor of 10. Similarly, N,N-dimethylacrylamide 26 and N-methyl-N-(3-pyridyl)acrylamide 27 undergo microsomal oxidation to form, via the 5-endo-trig cyclisation mode, 3-hydroxy-N-methyl-2-pyrrolidone 33 and 3-hydroxycotinine34, respectively, confirming the intermediacy of a carbon-centred radical in the dealkylation process.Attempts to trap N-acyliminium ions during microsomal dealkylation failed. Thus, although N,N-dimethylaniline 35 reacts in the presence of NaCN to form N-cyanomethyl-N-methylaniline 37 (NuCN), N,N-dimethylbenzamide undergoes dealkylation without forming N-cyanomethyl-N-methylbenzamide. Similarly, microsomal reaction of N,N-dimethylaniline in the presence of NaBD4 gives rise to multiple incorporation of deuterium atoms into the methyl groups of the starting material, whereas N,N-dimethylbenzamide undergoes dealkylation but with no such deuterium incorporation into the starting material. Further, microsomal oxidation of N,N-dimethylsalicylamide 38 yields N-methylsalicylamide 40 with no evidence for the formation of N-methyl-2,3-dihydro-4H-1,3-benzoxazin-4-one 39, the potential product of intramolecular cyclisation of the phenolic oxygen atom onto the putative N-aroylmethylene iminium ion. p

The role of monoamine oxidase (MAO) and cytochrome P450 (P450) in the oxidative deamination of primaquine by rat liver fractions was studied. Rat liver fractions including liver homogenate, mitochondria, microsomes and 100,000 g supematant fractions were prepared from a pool of rat livers and characterised using benzylamine as a probe for MAO activity and N,N-dimethylbenzamide as a probe for P450 N-dealkylation activity. Incubation of all fractions with primaquine yielded carboxyprimaquine as the only metabolite detectable by HPLC. The mitochondrial fraction, which contained MAO activity but not P450 activity, presented the highest Vmax/K(M) value for the formation of carboxyprimaquine (8.5 x 10(-6) dm3mg(-1)h(-1). A substantially lower Vmax/K(M) value (1.3 x 10(-6) dm3mg(-1)h(-1)) was obtained in the microsomal fraction, which contained P450 but not MAO activity. The liver homogenate fraction presented a similar value (1.8 x 10(-6) dm3mg(-1)h(-1), though it contained both enzyme systems. Incubations of all the fractions that presented MAO activity, in presence of the MAO inhibitor pargiline, resulted in a marked inhibition of primaquine oxidation. P450 inhibitor SKF 525-A effectively inhibited primaquine metabolism in the microsomal fraction but inhibition in the liver homogenate was less effective. The results are consistent with an important role for MAO in primaquine biotransformation, though clearly metabolism by P450 has a contribution role.

Purpose. Dipeptide derivatives of primaquine (PQ) with reduced oxidative deamination to the inactive metabolite carboxypnmaquine were synthesized and evaluated as a novel class of transmission-blocking antimalarials.

Tertiary acyloxymethylsulfonamides undergo hydrolysis via pH-independent and acid- and base-catalysed processes. Reactions are also buffer catalysed for buffer species with pKa values > ca. 10.5. For the pH-independent pathway, hydrolysis takes place via formation of an N-sulfonyl iminium ion. There is no general-base or nucleophilic catalysis in this region. The mechanism of the acid-catalysed process involves pre-equilibrium protonation of the substrate followed by iminium ion formation. General-acid catalysis is not observed. The base-catalysed pathway involves the normal BAc2 mechanism of ester hydrolysis. The buffer-catalysed reaction gives rise to a curved Bronsted plot, with β values of 1.6 and 0.25 for nucleophiles with pKa values 13, respectively. This is indicative of nucleophilic catalysis associated with a change in rate-limiting step from formation of the tetrahedral intermediate for buffer species with pKa > 13 to decomposition of the tetrahedral intermediate for buffer species with pKa

Kinetics of acid hydrolysis of 1-methyl-1-nitroso-3-p-tolylsulfonylguanidine 2 and of two 1-methyl-1-nitroso-3-benzoylguanidines (4-unsubstituted and 4-chloro) 5 and 6 have been studied. For the acid hydrolysis of 1-methyl-1-nitroso-3-p-tolylsulfonylguanidine 2, the absence of catalysis by thiocyanate ion, and the value of the kinetic solvent isotope effect indicate that either a rate determining proton transfer followed by fast denitrosation or a concerted pathway is involved in the mechanism. In the case of the acid hydrolysis of 1-methyl-1-nitroso-3-benzoylguanidines 5 and 6 it was observed that the protonated form decomposes via two parallel pathways. One involves a slow nucleophilic attack concerted with an intramolecular proton transfer, and the other a slow concerted denitrosation, where a second proton transfer and NO+ expulsion are simultaneous.

Reaction of tolazoline with N2O4 yields N-nitrotolazoline, the prototypical nitroamidine. N-Nitrotolazoline undergoes acid-catalysed hydrolysis of the nitroamidine function to form N-(2-hydroxyethyl)phenylacetamide. The observed pseudo-first-order rate constants, k0, have a non-linear dependence upon acidity, displaying saturation at higher acid concentrations consistent with a mechanism involving equilibrium protonation of N-nitrotolazoline prior to subsequent decomposition of the protonated intermediate. Reactions are subject neither to general acid- or base-catalysis nor to catalysis by thiocyanate ion. The solvent deuterium isotope effect for protonation was found to be 0.3, and for decomposition of the protonated intermediate, 1.7. A value of (–100 ± 5) J K–1 mol–1 was determined for ΔS ‡ for the decomposition step. Thus, hydrolysis of the protonated intermediate involves rapid attack of a molecule of water at the amidine carbon atom followed by a slow, intramolecular rearrangement involving proton transfer.

Purpose. The synthesis of chemically stable triazene prodrugs capable of hydrolysing under physiological conditions to liberate cytotoxic monomethyltriazene alkylating agents.

Purpose. Novel tertiary amidomethyl esters were synthesized and evaluated as potential prodrugs of carboxylic acid agents.

Purpose. O-(N-alkylamido)methyl esters of penicillin G were studied as a new class of prodrugs. Methods. Their hydrolysis in aqueous buffers containing 20 % (v/v) of acetonitrile was investigated by HPLC. Results. A U-shaped pH-rate profile was seen with a pH-independent process extending from pH ca. 2 to pH ca. 10. This pathway is characterised by kinetic data that are consistent with a uni-molecular mechanism involving rate-limiting iminium ion formation and penicillinoate expulsion. Penicillin G and the corresponding amide are the ultimate products detected and isolated, indicating that β-lactam ring opening is much slower than ester hydrolysis. The O-(N-alkylamido)methyl esters of penicillin G displayed similar in vitro antibacterial activity to penicillin G itself. Conclusions. Compared to the penicillin G derivatives, the much higher stability of the O-(N-methylbenzamido)methyl benzoate, acetate and valproate esters (which gave rise to a Bronsted βlg value of ca. -1) suggests that tertiary N-acyloxymethylamides may be useful prodrugs for carboxylic acid drugs with pKa >4.

Title compounds (VI) and (XVI) are synthesized starting from esters (I) or (XII), resp., via dipolar cycloaddition of nitrile oxides derived from the latter in situ with enamino-ester (III).

The in vitro metabolism of N,N-dialkylamides by phenobarbital-induced rat liver microsomes yields an N-alkylamide and the corresponding aldehyde. Although, N-hydroxymethyl-N-alkylamide intermediates can be detected from N-methyl-N-alkylamides, no N-hydroxyalkyl-N-alkylamide inter- mediates are detected from the N,N-dialkylamide substrates. Vmax values were independent of amide structure, whereas V max K m values were dependent on the lipophilidty of the N,N-dialkylbenazamide studied. These results suggest that diffusion of substrate into the membrane-bound enzyme active site limits the rate of the microsomal oxidation of the amides. Metabolism of N-alkyl-N-methylamides reveals identical values of Vmax for demethylation and dealkylation. Values of V max K m for demethylation depend upon the lipophilicity of the N-alkyl group, whereas V max K m values for dealkylation appear to be dependent upon the steric bulk of the alkyl group, particularly around the α-carbon. Moreover, V max K m values for demethylation are larger than for dealkylation, implying the reactions are under kinetic control. Comparison of the kinetic data with theoretical AMI semi-empirical molecular orbital calculations suggests a mechanism involving formation of a carbon-centred radical. Use of an N-cyclo-propylmethylbenzamide substrate to trap such a radical failed, presumably because oxygen rebound is faster than radical rearrangement. An N-cyclopropylamide substrate did not undergo metabolism of the cyclopropyl ring, consistent with carbon-centred radical, but not nitrogen radical cation, formation.

4,5-Dihydroimidazolium ylides generated by conjugate addition-proton transfer from dihydroimidazoles and double-activated electron-deficient alkenes afford 2 : 1 or 1 : 1 : 1 adducts in a one-pot process.

The synthesis, inhibitory activity and mode of action of oxazolidine-2,4-diones against porcine pancreatic elastase, here used as a model for human neutrophil elastase, are reported. The nature of N-substitution at the oxazolidine-2,4-dione scaffold has large effect on the inhibitory potency against elastase. N-Acyl and N-sulfonyloxazolidine-2,4-diones emerged as potent pseudo-irreversible inhibitors, displaying high second-order rate constants for PPE inactivation. The title compounds were also shown to be potent inhibitors of human neutrophil elastase (HNE) and proteinase-3, and weak inhibitors of human cathepsin G. The results herein presented show that the oxazolidine-2,4-diones represent a new promising class of serine protease inhibitors.

The hydrolysis of 1-aryl-3-acyl-3-methyltriazenes in aqueous sulfuric acid is described. The 3-formyl derivative undergoes an acid-catalysed deacylation reaction, characterised by a monotonic rise in the pseudo-first-order rate constant, k0 with increasing acidity, solvent deuterium isotope effects, kH2SO4/kD2SO4, of 0.9 (at 0.95 mol dm–3 H2SO4) and 0.8 (at 2.85 mol dm–3 H2SO4) and an entropy of activation of –80 J mol–1 K–1. The 3-alkanoyl derivatives also undergo acid-catalysed decomposition involving cleavage of either the N3–C acyl bond or the N2–N3 triazene bond. Below 3 mol dm–3 H2SO4, only acyl bond cleavage is observed. At higher acidities the extent of N2–N3 bond cleavage increases. The reaction is characterised by (i) solvent deuterium isotope effects of ca. 0.6 at 2 and 5 mol dm–3 H2SO4 and ca. 0.4 at 8 mol dm–3 H2SO4, (ii)ΔS‡ values of –6.7 and –51 J mol–1 K–1 at 2 and 6.1 mol dm–3 H2SO4, respectively, (iii) Hammett ρ values for the substituent in the triazene N-aryl ring of –0.7 and –0.9 at 3 and 9 mol dm–3 H2SO4, respectively, and (iv) an increase in reactivity with electron donating ability of the alkyl substituent of the acyl group. The 3-trifluoroacetyl triazenes are subject to solvolysis of the neutral, as well as the protonated, substrate. The hydrolysis of the neutral substrate involves N–acyl bond cleavage and is characterised by a solvent deuterium isotope effect, kH2O/kD2O, of 2.4, and a Hammett ρ value of +0.8 for the substituent in the N-aryl ring. The reactivity of the neutral substrate diminishes with increasing acidity until 6 mol dm–3 H2SO4, beyond which acid-catalysed N–acyl bond cleavage predominates, for which the solvent isotope effect, kH2SO4/kD2SO4, is 0.8 and the Hammett ρ value –0.5. The 3-aroyl substrates suffer acid-catalysed decomposition, the extent of the N2–N3 bond cleavage process being greater than for the N-alkanoyl counterparts. The reactions are rationalised in terms of a process that involves pre-equilibrium protonation of the substrate either at the N1 triazene atom or the amide oxygen atom, followed by subsequent decomposition of the protonated substrate via either N3–C bond cleavage, involving attack of water at the amide carbonyl, or unimolecular N2–N3 bond cleavage. The relative extents of the N3–C and N2–N3 bond cleavage processes depend on the reactivity of the acyl group and the water activity; the higher the water activity and the more reactive the acyl group, the more deacylation is favoured.

N-Arylbenzimidoyl chlorides, in which the N-aryl group is unsubstituted at the ortho- and para-positions, react with AgNO3 to yield N-(nitroaryl)benzamides in which the NO2 group resides in the ortho- or para-position. N-Arylbenzimidoyl chlorides, in which the N-aryl ring is 2,4,6-trisubstituted, react with AgNO3 to yield the corresponding N-aryl-N-nitrobenzamides. The formation of both types of product can be explained by the intermediacy of an O-nitro imidate. Spectroscopic and chemical evidence is presented for the formation of this intermediate in the reaction of N-(2,4,6-trisubstituted phenyl)benzimidoyl chlorides with AgNO3. Rearrangement of the O-nitro imidate is unimolecular and intramolecular. The rate of rearrangement is independent of the substituent in the C-aryl ring, but increases with the electron-withdrawing ability of the substituents in the N-aryl ring. A mechanism is proposed in which the imidoyl chloride reacts with AgNO3 to produce first a nitrilium ion which goes on to form an O-nitro imidate that subsequently rearranges via a homolytic cleavage of the O–NO2 bond. The ortho:para ratios of N-(nitroaryl)benzamides obtained in the present work indicate that O-nitro imidates are not responsible for the high ½ortho:para ratios sometimes observed in the nitration of anilides. N-Alkylbenzimidoyl chlorides react with AgNO3 to form the corresponding N-nitro- and N-nitrosobenzamides. The mechanism of formation of the N-alkyl-N-nitrobenzamide arises from a pathway analogous to that for N-aryl-N-nitrobenzamides, involving a nitrilium ion that gives rise to an O-nitro imidate. The evidence for the formation of the N-nitrosobenzamide points to an alternative reaction of the imidoyl chloride with AgNO3. One possible mechanism for this reaction is described.

Acyloxymethyl derivatives of secondary and tertiary amides undergo hydrolysis via. acid-catalysed, base-catalysed and pH-independent processes. The pH-independent pathway involves rate-limiting iminium ion formation and is characterised by the following: a Hammett ρ value for the substituent in the benzamide moiety of ca.–1.2 for both types of substrate; the absence of general-base or nucleophilic catalysis; a common benzoate ion effect; a solvent deuterium isotope effect, kobsH2O/kobsD2O, of ca. 1.6; ΔS‡ values of –4 and –12 J K–1 mol–1 for secondary and tertiary substrates respectively; and higher reactivity of the tertiary amides over their secondary counterparts. The acid-catalysed process involves protonation of the substrate followed by iminium ion formation, and is characterised by the following: a Hammett ρ value of ca.–1.5 for the substituent effect of the benzamide moiety; a solvent deuterium isotope effect of ca. 0.4; a monotonic rise in the pseudo-first-order rate constant kobs with increasing [H2SO4]; ΔS‡ values > 0 J K–1 mol–1; higher reactivity of the tertiary substrates over their secondary counterparts; and a value of 0.85 for the Bronsted coefficient, βIg for the carboxylate nucleofuge. The base-catalysed hydrolysis of tertiary substrates involves normal ester hydrolysis via. acyl–oxygen bond cleavage, and is characterised by a Hammett ρ value of +0.38, a solvent deuterium isotope effect, kOH–/kOD–, of 0.85, and a ΔS‡ value of –96 J K–1 mol–1. The corresponding base-catalysed process for the secondary substrates involves imine formation via an E2 elimination reaction. The secondary acyloxymethylamides are some 7 × 104 times more reactive than their tertiary counterparts in the base-catalysed region. Hammett ρ values of +1.1 and +0.6 are obtained for the substituents in the ester and amide moieties, respectively. Buffer catalysis is observed, and the value of ca. 0.5 for the Bronsted β coefficient identifies the amide proton as approximately 50% transferred to the buffer species in the transition state.Heats of formation, ΔHf, calculated using the AM1 SCF MO package reveal that iminium ion formation is thermodynamically equi-energetic for cyclic and acyclic systems. Iminium ion formation from tertiary substrates is favoured by ca. 25 kJ mol–1 over the corresponding secondary analogues.

S-Cysteinyl-, S-(N-acetyl)cysteinyl-, S-glutathionyl and some related thioether derivatives of anticancer triazenes have been synthesised in high yield. The synthesis involves reaction between N-alkyl-N-hydroxymethyltriazenes with cysteine, N-acetylcysteine, glutathione or appropriate thiol in trifluoroacetic acid. The cysteinyl derivative is not a substrate for a mammalian β-lyase. Consequently the cysteinyl, N-acetylcysteinyl and glutathionyl derivatives lack anticancer activity against the Walker, L1210 and V79 tumour cell lines, mutagenic activity against Salmonella TA 100 and TA 2638 cell lines and cytotoxicity against renal proximal tubule cells.

N-Alkyl-N-chloromethylamides 2, prepared from secondary amides, paraformaldehyde and chlorotrimethylsilane, react readily with carboxylate anions to generate the corresponding tertiary N-acyloxymethylamides 3 in good yield; the latter give rise to the parent carboxylic acids in aqueous media at pH 7.4 and 37 °C with half-lives between ca. 1 min and 42 h.

Tertiary sulfonylcarbamates 1 were prepared by reaction of a sulfonamide anion with aryl chloroformates. These previously unreported compounds hydrolyse in aqueous media to the parent sulfonamide and phenol. The pH–rate profile shows both spontaneous and base-catalysed processes. The reaction is also catalysed by buffers. Kinetic data for the hydrolysis of these compounds by HO− are best interpreted in terms of a mechanism involving rate-limiting formation of a tetrahedral intermediate from nucleophilic attack of hydroxide ion at the carbamate carbonyl carbon atom. For the 4-nitrophenylsulfonyl compound 1h decomposition of the tetrahedral intermediate appears to be rate-limiting with the sulfonamide anion, rather than the phenoxide, functioning as the leaving group. The buffer-catalysed process is consistent with general base-catalysed attack of water at the carbamate carbonyl carbon atom.

We report here a simple entry into naphtho[2,3-d]isoxazole-4,9-dione system containing a EWG in position 3 using the readily available 2,3-dichloro-1,4-naphthoquinone and nitromethyl derivatives in the presence of base. Antifungal activity of synthesised naphthoquinones was evaluated against ATCC and PYCC reference strains of Candida. The results suggest that the naphtho[2,3-d]isoxazole-4,9-dione scaffold has the potential to be developed into novel and safe therapeutic antifungal agents.

A series of N-acyloxymethyl- and N-aminocarbonyloxymethyl derivatives of 2-azetidinones, 3, with different substituent patterns at the beta-lactam C-3 and C-4 positions, were designed as potential mechanism-based inhibitors for human leukocyte elastase and found to exhibit inhibitory potency and selectivity for the enzyme.

4,5-Dihydroimidazoles undergo an N-alkylation and 1,3-dipolar cycloaddition cascade with unsaturated α-bromoketones, with subsequent eliminative ring-opening, recyclisation and tautomerisation to form unexpected hexahydropyrrolo[1,2,3-de]quinoxalines.

N -(2-iodoethyl) and N -(3-iodopropyl)pyrimidines and purines undergo stereoselective conjugate radical addition with an optically active oxazolidinone acceptor to give syn -adducts that can be converted into amino acids carrying pyrimidine and purine (nucleobase) side chains.

The conformationally restricted tertiary amides N-methyl-2-pyrrolidone 6, N-methyl-2-piperidone 7 and N-methyl-e-caprolactam 8 were oxidised by 5,10,15,20-tetraphenylporphyrinatoiron(III) chloride/tert-butyl hydroperoxide (TPPFe/ButOOH) and by phenobarbital-induced rat liver microsomes. The products were the N-demethylated lactams together with the analogous N-methylimides and norimides. For the TPPFe/ButOOH reaction ring oxidation is preferred to N-demethylation, paralleling the relative stabilities of the corresponding intermediate carbon-centred radicals as calculated by the AM1 semi-empirical method. In contrast, the microsomal reaction of the N-methyllactams strongly favours N-demethylation, demonstrating that hydrogen atom abstraction from the alkyl group Z to the amide carbonyl oxygen atom is preferred. The chiral tertiary amides N-methyl-N-(1-phenylethyl)benzamide 9 and N-methyl-5-phenyl-2-pyrrolidone 10 were also oxidised by TPPFe/ButOOH and by phenobarbital-induced rat liver microsomes. Using TPPFe/ButOOH, loss of the secondary alkyl group of 9 is preferred by a factor of ca. 6. Similarly, ring oxidation of 10 is favoured over demethylation by a factor of 9. For the microsomal reaction of (R)-9 dealkylation is preferred over demethylation by a factor of 1.7, whereas for (S)-9 demethylation is favoured by a factor of 1.25. For the microsomal reaction of (R)-10 and (S)-10 ring oxidation at the 5-position of the pyrrolidone ring is preferred over demethylation by factors of ca. 4 and 9 for the two isomers, respectively, and the (S)-enantiomer undergoes ring oxidation 2–3 times more readily than the (R)-enantiomer. For both 9 and 10 there is negligible stereochemical influence of the chiral centre upon the N-demethylation reaction. The results show that the stereochemical preference of the microsomal N-dealkylation reaction is modest.