Mechanism of inhibition of LDL phospholipase A2 by monocyclic-beta-lactams. Burst kinetics and the effect of stereochemistry

Mechanism of oxidized phospholipid-related inflammatory response in vascular ageing

Vascular ageing is an important factor in the morbidity and mortality of the elderly. Atherosclerosis is a characteristic disease of vascular ageing, which is closely related to the enhancement of vascular inflammation. Phospholipid oxidation products are important factors in inducing cellular inflammation. Through interactions with vascular cells and immune cells, they regulate intracellular signaling pathways, activate the expression of various cytokines, and affect cell behavior, such as metabolic level, proliferation, apoptosis, etc. Intervention in lipid metabolism and anti-inflammation are the two key pathways of drugs for the treatment of atherosclerosis. This review aims to sort out the signaling pathway of oxidized phospholipids-induced inflammatory factors in vascular cells and immune cells and the mechanism leading to changes in cell behavior, and summarize the therapeutic targets in the inflammatory signaling pathway for the development of atherosclerosis drugs.

Platelet activating-factor acetylhydrolase II: A member of phospholipase A2 family that hydrolyzes oxidized phospholipids

Intracellular platelet activating-factor acetylhydrolase type II (PAF-AH II) is a 40-kDa monomeric enzyme. It was originally identified as an enzyme that hydrolyzes the acetyl group of PAF (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine). As a member of phospholipase A2 super family, PAF-AH II has broad substrate specificity. It can hydrolyze phospholipids with relatively short-length or oxidatively modified sn-2 chains which endows it with various functions such as protection against oxidative stress, transacetylase activity and producing lipid mediators. PAF-AH II has been proven to be involved in several diseases such as allergic diseases, oxidative stress-induced injury and ischemia injury, thus it has drawn more attention from researchers. In this paper, we outline an entire summary of PAF-AH II, including its structure, substrate specificity, activity assay, inhibitors and biological activities.

C4-Phenylthio β-lactams: Effect of the chirality of the β-lactam ring on antimicrobial activity

C4-phenylthio β-lactams are a new family of antibacterial agents that have activity against two phylogenetically distant bacteria - Mycobacterium tuberculosis (Mtb) and Moraxella catarrhalis (M. cat). These compounds are effective against β-lactamase producing Mtb and M. cat unlike the clinically relevant β-lactam antibiotics. The structure-activity relationship for the C4 phenylthio β-lactams has not yet been completely defined. Earlier efforts in our laboratories established that the C4-phenylthio substituent is essential for antimicrobial activity, while the N1 carbamyl substituent plays a more subtle role. In this present study, we investigated the role that the stereochemistry at C4 plays in these compounds' antibacterial activity. This was achieved by synthesizing and testing the antimicrobial activity of diastereomers with a chiral carbamyl group at N1. Our findings indicate that a strict stereochemistry for the C4-phenylthio β-lactams is not required to obtain optimal anti-Mtb and anti-M. cat activity. Furthermore, the structure-bioactivity profiles more closely relate to the electronic requirement of the phenylthiogroup. In addition, the MICs of Mtb are sensitive to growth medium composition. Select compounds showed activity against non-replicating and multi-drug resistant Mtb.

Lipoprotein-associated phospholipase A2: The story continues

Inflammation is thought to play an important role in the pathogenesis of vascular diseases. Lipoprotein-associated phospholipase A2 (Lp-PLA2) mediates vascular inflammation through the regulation of lipid metabolism in blood, thus, it has been extensively investigated to identify its role in vascular inflammation-related diseases, mainly atherosclerosis. Although darapladib, the most advanced Lp-PLA2 inhibitor, failed to meet the primary endpoints of two large phase III trials in atherosclerosis patients cotreated with standard medical care, the research on Lp-PLA2 has not been terminated. Novel pathogenic, epidemiologic, genetic, and crystallographic studies regarding Lp-PLA2 have been reported recently, while novel inhibitors were identified through a fragment-based lead discovery strategy. More strikingly, recent clinical and preclinical studies revealed that Lp-PLA2 inhibition showed promising therapeutic effects in diabetic macular edema and Alzheimer's disease. In this review, we not only summarized the knowledge of Lp-PLA2 established in the past decades but also emphasized new findings in recent years. We hope this review could be valuable for helping researchers acquire a much deeper insight into the nature of Lp-PLA2, identify more potent and selective Lp-PLA2 inhibitors, and discover the potential indications of Lp-PLA2 inhibitors.

pCRP-mCRP Dissociation Mechanisms as Potential Targets for the Development of Small-Molecule Anti-Inflammatory Chemotherapeutics

Circulating C-reactive protein (CRP) is a key acute-phase protein and one of the main clinical biomarkers for inflammation and infection. CRP is an important upstream mediator of inflammation and is associated with the onset of a number of important disease states including cardiovascular disease and neurodegenerative disorders such as Alzheimer’s disease. This pentraxin exerts pro-inflammatory properties via dissociation of the pentamer (pCRP) to a monomeric form (mCRP). This dissociation is induced by binding of pCRP to cell surface phosphocholine residues exposed by the action of phospholipase A₂ (PLA₂). Given the association of CRP with the onset of a range of serious disease states this CRP dissociation process is a tempting drug target for the development of novel small-molecule therapeutics. This review will discuss potential targets for chemotherapeutic intervention elucidated during studies of CRP-mediated inflammation and provide an up-to-date summary of the development of small molecules, not only targeted directly at inhibiting conversion of pCRP to mCRP, but also those developed for activity against PLA₂, given the key role of this enzyme in the activation of CRP.

Regioselectivity of thiouracil alkylation: Application to optimization of Darapladib synthesis

Darapladib is one of the most potent Lp-PLA₂ (Lipoprotein-associated phospholipase A₂) inhibitor with an IC₅₀ of 0.25 nM. We demonstrate that a crucial step of Darapladib synthesis was not correctly described in the literature, leading to the production of wrong regioisomers. Moreover we show that the inhibitory activity is directly linked to the position on N1 since compounds bearing alkylation on different sites have potentially less interaction within the active site of Lp-PLA₂.

Structure-Guided Discovery of Novel, Potent, and Orally Bioavailable Inhibitors of Lipoprotein-Associated Phospholipase A2

Lipoprotein-associated phospholipase A2 (Lp-PLA2) is a promising therapeutic target for atherosclerosis, Alzheimer's disease, and diabetic macular edema. Here we report the identification of novel sulfonamide scaffold Lp-PLA2 inhibitors derived from a relatively weak fragment. Similarity searching on this fragment followed by molecular docking leads to the discovery of a micromolar inhibitor with a 300-fold potency improvement. Subsequently, by the application of a structure-guided design strategy, a successful hit-to-lead optimization was achieved and a number of Lp-PLA2 inhibitors with single-digit nanomolar potency were obtained. After preliminary evaluation of the properties of drug-likeness in vitro and in vivo, compound 37 stands out from this congeneric series of inhibitors for good inhibitory activity and favorable oral bioavailability in male Sprague-Dawley rats, providing a quality candidate for further development. The present study thus clearly demonstrates the power and advantage of integrally employing fragment screening, crystal structures determination, virtual screening, and medicinal chemistry in an efficient lead discovery project, providing a good example for structure-based drug design.

Design of Benzoxathiazin-3-one 1,1-Dioxides as a New Class of Irreversible Serine Hydrolase Inhibitors: Discovery of a Uniquely Selective PNPLA4 Inhibitor

The design and examination of 4,1,2-benzoxathiazin-3-one 1,1-dioxides as candidate serine hydrolase inhibitors are disclosed, and represent the synthesis and study of a previously unexplored heterocycle. This new class of activated cyclic carbamates provided selective irreversible inhibition of a small subset of serine hydrolases without release of a leaving group, does not covalently modify active site catalytic cysteine and lysine residues of other enzyme classes, and was found to be amenable to predictable structural modifications that modulate intrinsic reactivity or active site recognition. Even more remarkable and within the small pilot series of candidate inhibitors examined in an initial study, an exquisitely selective inhibitor for a poorly characterized serine hydrolase (PNPLA4, patatin-like phospholipase domain-containing protein 4) involved in adipocyte triglyceride homeostasis was discovered.

Structural and Thermodynamic Characterization of Protein-Ligand Interactions Formed between Lipoprotein-Associated Phospholipase A2 and Inhibitors

Lipoprotein-associated phospholipase A2 (Lp-PLA2) represents a promising therapeutic target for atherosclerosis and Alzheimer's disease. Here we reported the first crystal structures of Lp-PLA2 bound with reversible inhibitors and the thermodynamic characterization of complexes. High rigidity of Lp-PLA2 structure and similar binding modes of inhibitors with completely different scaffolds are revealed. It not only provides the molecular basis for inhibitory activity but also sheds light on the essential features of Lp-PLA2 recognition with reversible inhibitors.

Identification of selective covalent inhibitors of platelet activating factor acetylhydrolase 1B2 from the screening of an oxadiazolone-capped peptoid-azapeptoid hybrid library

A potent and selective inhibitor of platelet-activating factor acetylhydrolase 1B2 (PAFAH1B2) is described. The compound was derived by improvement of a modest affinity primary hit isolated from the screening of a bead-displayed peptoid-azapeptoid hybrid library tethered to an oxadiazolone 'warhead'. The oxadiazolone moiety of the inhibitors was found to react covalently with the active site serine residue of PAFAH1B2. This screening strategy may be useful for the identification of many selective, covalent inhibitors of serine hydrolases.

Discovery of Potent and Orally Active Lipoprotein-Associated Phospholipase A2 (Lp-PLA2) Inhibitors as a Potential Therapy for Diabetic Macular Edema

Lipoprotein-associated phospholipase A2 (Lp-PLA2) is considered to be a promising therapeutic target for several inflammation-associated diseases. Herein, we describe the discovery of a series of pyrimidone derivatives as Lp-PLA2 inhibitors. Systematic structural modifications led to the identification of several pyrimidone compounds with promising in vitro inhibitory potency and pharmacokinetic properties. Compound 14c, selected for in vivo evaluation, demonstrated decent pharmacokinetic profiles and robust inhibitory potency against Lp-PLA2 in Sprague-Dawley (SD) rats. Furthermore, 14c significantly inhibited retinal thickening in STZ-induced diabetic SD rats as a model of diabetic macular edema (DME) after oral dosing for 4 weeks. Taken together, these results suggested that 14c can serve as a valuable lead in the search for new Lp-PLA2 inhibitors for prevention and/or treatment of DME.

Proteome-wide reactivity profiling identifies diverse carbamate chemotypes tuned for serine hydrolase inhibition

Serine hydrolases are one of the largest and most diverse enzyme classes in Nature. Inhibitors of serine hydrolases are used to treat many diseases, including obesity, diabetes, cognitive dementia, and bacterial and viral infections. Nonetheless, the majority of the 200+ serine hydrolases in mammals still lack selective inhibitors for their functional characterization. We and others have shown that activated carbamates, through covalent reaction with the conserved serine nucleophile of serine hydrolases, can serve as useful inhibitors for members of this enzyme family. The extent to which carbamates, however, cross-react with other protein classes remains mostly unexplored. Here, we address this problem by investigating the proteome-wide reactivity of a diverse set of activated carbamates in vitro and in vivo, using a combination of competitive and click chemistry (CC)-activity-based protein profiling (ABPP). We identify multiple classes of carbamates, including O-aryl, O-hexafluoroisopropyl (HFIP), and O-N-hydroxysuccinimidyl (NHS) carbamates that react selectively with serine hydrolases across entire mouse tissue proteomes in vivo. We exploit the proteome-wide specificity of HFIP carbamates to create in situ imaging probes for the endocannabinoid hydrolases monoacylglycerol lipase (MAGL) and α-β hydrolase-6 (ABHD6). These findings, taken together, designate the carbamate as a privileged reactive group for serine hydrolases that can accommodate diverse structural modifications to produce inhibitors that display exceptional potency and selectivity across the mammalian proteome.

Selective inhibitors and tailored activity probes for lipoprotein-associated phospholipase A(2)

Lipoprotein-associated phospholipase A(2) (Lp-PLA(2) or PLA(2)G7) binds to low-density lipoprotein (LDL) particles, where it is thought to hydrolyze oxidatively truncated phospholipids. Lp-PLA(2) has also been implicated as a pro-tumorigenic enzyme in human prostate cancer. Several inhibitors of Lp-PLA(2) have been described, including darapladib, which is currently in phase 3 clinical development for the treatment of atherosclerosis. The selectivity that darapladib and other Lp-PLA(2) inhibitors display across the larger serine hydrolase family has not, however, been reported. Here, we describe the use of both general and tailored activity-based probes for profiling Lp-PLA(2) and inhibitors of this enzyme in native biological systems. We show that both darapladib and a novel class of structurally distinct carbamate inhibitors inactivate Lp-PLA(2) in mouse tissues and human cell lines with high selectivity. Our findings thus identify both inhibitors and chemoproteomic probes that are suitable for investigating Lp-PLA(2) function in biological systems.

Potential human cholesterol esterase inhibitor design: benefits from the molecular dynamics simulations and pharmacophore modeling studies

Human pancreatic cholesterol esterase (hCEase) is one of the lipases found to involve in the digestion of large and broad spectrum of substrates including triglycerides, phospholipids, cholesteryl esters, etc. The presence of bile salts is found to be very important for the activation of hCEase. Molecular dynamic simulations were performed for the apoform and bile salt complexed form of hCEase using the co-ordinates of two bile salts from bovine CEase. The stability of the systems throughout the simulation time was checked and two representative structures from the highly populated regions were selected using cluster analysis. These two representative structures were used in pharmacophore model generation. The generated pharmacophore models were validated and used in database screening. The screened hits were refined for their drug-like properties based on Lipinski's rule of five and ADMET properties. The drug-like compounds were further refined by molecular docking simulation using GOLD program based on the GOLD fitness score, mode of binding, and molecular interactions with the active site amino acids. Finally, three hits of novel scaffolds were selected as potential leads to be used in novel and potent hCEase inhibitor design. The stability of binding modes and molecular interactions of these final hits were re-assured by molecular dynamics simulations.

The pharmacological landscape and therapeutic potential of serine hydrolases

Serine hydrolases perform crucial roles in many biological processes, and several of these enzymes are targets of approved drugs for indications such as type 2 diabetes, Alzheimer's disease and infectious diseases. Despite this, most of the human serine hydrolases (of which there are more than 200) remain poorly characterized with respect to their physiological substrates and functions, and the vast majority lack selective, in vivo-active inhibitors. Here, we review the current state of pharmacology for mammalian serine hydrolases, including marketed drugs, compounds that are under clinical investigation and selective inhibitors emerging from academic probe development efforts. We also highlight recent methodological advances that have accelerated the rate of inhibitor discovery and optimization for serine hydrolases, which we anticipate will aid in their biological characterization and, in some cases, therapeutic validation.

Nonsteroidal Anti-Inflammatory Drugs (NSAIDs): Progress in Small Molecule Drug Development

Ever since the discovery of aspirin, small molecule therapeutics have been widely prescribed to treat inflammation and pain. Aspirin and several small molecule NSAIDs are known to inhibit the enzymes cyclooxygenase-1 (COX-1) and -2 (COX-2). Despite the success of NSAIDs to treat inflammatory disorders, the development of a clinically useful small molecule NSAIDs with decreased side effect profiles is an ongoing effort. The recent discovery and development of selective COX-2 inhibitors was a step toward this direction. Emerging trends are represented by the progress in the development of hybrid agents such as nitric oxide donor-NSAIDs (NO-NSAIDs) and dual COX/lipoxygenase (LOX) inhibitors. This review focuses on the recent advances in the rational design of small molecule NSAIDs in therapy.

Mechanism of Gly-Pro-pNA cleavage catalyzed by dipeptidyl peptidase-IV and its inhibition by saxagliptin (BMS-477118)

Dipeptidyl peptidase-IV (DPP-IV) is a serine protease with a signature Asp-His-Ser motif at the active site. Our pH data suggest that Gly-Pro-pNA cleavage catalyzed by DPP-IV is facilitated by an ionization of a residue with a pK of 7.2 +/- 0.1. By analogy to other serine proteases this pK is suggestive of His-Asp assisted Ser addition to the P1 carbonyl carbon of the substrate to form a tetrahedral intermediate. Solvent kinetic isotope effect studies yielded a D2Okcat/Km=2.9+/-0.2 and a D2Okcat=1.7+/-0.2 suggesting that kinetically significant proton transfers contribute to rate limitation during acyl intermediate formation (leaving group release) and hydrolysis. A "burst" of product release during pre steady-state Gly-Pro-pNA cleavage indicated rate limitation in the deacylation half-reaction. Nevertheless, the amplitude of the burst exceeded the enzyme concentration significantly (approximately 15-fold), which is consistent with a branching deacylation step. All of these data allowed us to better understand DPP-IV inhibition by saxagliptin (BMS-477118). We propose a two-step inhibition mechanism wherein an initial encounter complex is followed by covalent intermediate formation. Final inhibitory complex assembly (kon) depends upon the ionization of an enzyme residue with a pK of 6.2 +/- 0.1, and we assigned it to the catalytic His-Asp pair which enhances Ser nucleophilicity for covalent addition. An ionization with a pK of 7.9 +/- 0.2 likely reflects the P2 terminal amine of the inhibitor hydrogen bonding to Glu205/Glu206 in the enzyme active site. The formation of the covalent enzyme-inhibitor complex was reversible and dissociated with a koff of (5.5 +/- 0.4) x 10(-5) s(-1), thus yielding a Ki* (as koff/kon) of 0.35 nM, which is in good agreement with the value of 0.6 nM obtained from steady-state inhibition studies. Proton NMR spectra of DPP-IV showed a downfield resonance at 16.1 ppm. Two additional peaks in the 1H NMR spectra at 17.4 and 14.1 ppm were observed upon mixing the enzyme with saxagliptin. Fractionation factors (phi) of 0.6 and 0.5 for the 17.4 and 14.1 ppm peaks, respectively, are suggestive of short strong hydrogen bonds in the enzyme-inhibitor complex.

4-Alkyliden-β-lactams conjugated to polyphenols: Synthesis and inhibitory activity

A series of compounds combining the beta-lactam and polyphenol scaffold have been prepared and evaluated for inhibition of human leukocyte elastase and matrix metallo-proteases MMP-2 and MMP-9. The design of these compounds has been based on the 'overlapping-type' strategy where two pharmacophores are linked in a single molecule. The most powerful compound against elastase was an N-galloyl-4-alkyliden beta-lactam, [3-[1-(tert-butyl-dimethyl-silanyloxy)-ethyl]-4-oxo-1-(3,4,5-tris-benzyloxy-benzoyl)-azetidin-2-ylidene]-acetic acid ethylester, with an IC50 of 0.5 microM; while the most powerful against MMP-2 was a 4-alkyliden beta-lactam arylated on the C-3 hydroxy side chain (3,5-bis-benzyloxy-4-hydroxy-benzoic acid 1-(2-benzyloxycarbonylmethylene-4-oxo-azetidin-3-yl)-ethyl ester) with an IC50 of 4 microM. Of the total 35 compounds tested, high levels of inhibition of elastase and of MMPs were separately exerted by distinct molecules.

Novel lipoglycopeptides as inhibitors of bacterial signal peptidase I

Signal peptidase (SPase) I is responsible for the cleavage of signal peptides of many secreted proteins in bacteria. Because of its unique physiological and biochemical properties, it serves as a potential target for development of novel antibacterial agents. In this study, we report the production, isolation, and structure determination of a family of structurally related novel lipoglycopeptides from a Streptomyces sp. as inhibitors of SPase I. Detailed spectroscopic analyses, including MS and NMR, revealed that these lipoglycopeptides share a common 14-membered cyclic peptide core, an acyclic tripeptide chain, and a deoxy-alpha-mannose sugar, but differ in the degree of oxidation of the N-methylphenylglycine residue and the length and branching of the fatty acyl chain. Biochemical analysis demonstrated that these peptides are potent and competitive inhibitors of SPase I with K(i) 50 to 158 nm. In addition, they showed modest antibacterial activity against a panel of pathogenic Gram-positive and Gram-negative bacteria with minimal inhibitory concentration of 8-64 microm against Streptococcus pneumonniae and 4-8 microm against Escherichia coli. Notably, they mechanistically blocked the protein secretion in whole cells as demonstrated by inhibiting beta-lactamase release from Staphylococcus aureus. Taken together, the present discovery of a family of novel lipoglycopeptides as potent inhibitors of bacterial SPase I may lead to the development of a novel class of broad-spectrum antibiotics.

Lipoprotein-associated phospholipase A2: a potential new risk factor for coronary artery disease and a therapeutic target

The recognition that atherosclerosis represents an inflammatory disease has begun to shift interest towards novel therapies that could specifically target the underlying inflammatory component of atherogenesis. Like low-density lipoprotein, an ideal new drug target would be a modifiable plasma risk factor that not only reflects the ongoing inflammatory process but also actively promotes it. Lipoprotein-associated phospholipase A2, also known as platelet-activating factor acetylhydrolase, is a new risk factor that may have the potential to fulfil these requirements.

N-1 substituted pyrimidin-4-ones: novel, orally active inhibitors of lipoprotein-associated phospholipase A2

From two related series of 2-(alkylthio)-pyrimidones, a novel series of 1-((amidolinked)-alkyl)-pyrimidones has been designed as nanomolar inhibitors of human lipoprotein-associated phospholipase A2. These compounds show greatly enhanced activity in isolated plasma. Selected derivatives such as compounds 51 and 52 are orally active with a good duration of action.

Quantitative structure-activity relationships for the pre-steady-state inhibition of cholesterol esterase by 4-nitrophenyl-N-substituted carbamates

4-Nitrophenyl-N-substituted carbamates (1-6) are the pseudo-substrate inhibitors of porcine pancreatic cholesterol esterase. Thus, the first step of the inhibition (Ki step) is the formation of the enzyme inhibitor tetrahedral adduct and the second step of the inhibition (kc) is the formation of the carbamyl enzyme. The formation of the enzyme inhibitor tetrahedral adduct is further divided into two steps, the formation of the enzyme-inhibitor complex with the dissociation constant, KS, at the first step and the formation of the enzyme-inhibitor tetrahedral adduct from the complex at the second step. The two-step mechanism for the formation of the enzyme-inhibitor tetrahedral adduct is confirmed by the pre-steady-state kinetics. The results of quantitative structure-activity relationships for the pre-steady-state inhibitions of cholesterol esterase by carbamates 1-6 indicate that values of -logKs and logk2/k-2 are correlated with the Taft substituent constant, sigma*, and the rho* values from these correlations are -0.33 and 0.1, respectively. The negative rho* value for the -logKS-sigma*-correlation indicates that the first step of the two-step formation of the enzyme-inhibitor tetrahedral adduct (KS step) is the formation of the positive enzyme inhibitor complex. The positive rho* value for the logk2/k-2 -sigma*-correlation indicates that the enzyme inhibitor tetrahedral adduct is more negative than the enzyme inhibitor complex. Finally, the two-step mechanism for the formation of the enzyme inhibitor tetrahedral adduct is proposed according to these results. Thus, the partially positive charge is developed at nitrogen of carbamates 1-6 in the enzyme-inhibitor complex probably due to the hydrogen bonding between the lone pair of nitrogen of carbamates 1-6 and the amide hydrogen of the oxyanion hole of the enzyme. The second step of the two-step formation of the enzyme-inhibitor tetrahedral adduct is the nucleophilic attack of the serine of the enzyme to the carbonyl group of carbamates 1-6 in the enzyme-inhibitor complex and develops the negative-charged oxygen in the adduct.

The structure and mechanism of bacterial type I signal peptidases. A novel antibiotic target

Type I signal peptidases are essential membrane-bound serine proteases that function to cleave the amino-terminal signal peptide extension from proteins that are translocated across biological membranes. The bacterial signal peptidases are unique serine proteases that utilize a Ser/Lys catalytic dyad mechanism in place of the classical Ser/His/Asp catalytic triad mechanism. They represent a potential novel antibiotic target at the bacterial membrane surface. This review will discuss the bacterial signal peptidases that have been characterized to date, as well as putative signal peptidase sequences that have been recognized via bacterial genome sequencing. We review the investigations into the mechanism of Escherichia coli and Bacillus subtilis signal peptidase, and discuss the results in light of the recent crystal structure of the E. coli signal peptidase in complex with a beta-lactam-type inhibitor. The proposed conserved structural features of Type I signal peptidases give additional insight into the mechanism of this unique enzyme.

2-(Alkylthio)pyrimidin-4-ones as novel, reversible inhibitors of lipoprotein-associated phospholipase A2

Starting from two weakly active hits from high throughput screening, a novel series of 2-(alkylthio)-pyrimidin-4-ones with high potency and selectivity for lipoprotein-associated phospholipase A2 has been designed. In contrast to previously known inhibitors, these have been shown to act by a non-covalent and substrate competitive mechanism.

Novel mechanism of inhibition of elastase by beta-lactams is defined by two inhibitor crystal complexes

Two structurally related beta-lactams form different covalent complexes upon reaction with porcine elastase. The high resolution x-ray structures of these two complexes provide a clear insight into the mechanism of the reaction and suggest the design of a new class of serine protease inhibitors that resist enzyme reactivation by hydrolysis of the acyl intermediate. The presence of a hydroxyethyl substituent on the beta-lactam ring provides a new reaction pathway resulting in the elimination of the hydroxyethyl group and the formation of a stabilizing conjugated double bond system. In contrast, the presence of a diethyl substituent on the beta-lactam ring leads to addition of water. The two enzyme complexes show very different binding modes in the enzyme active site.

Structure-reactivity probes for active site shapes of cholesterol esterase by carbamate inhibitors

4,4'-Biphenyl-di-N-butylcarbamate (1), (S)-1,1'-bi-2-naphthyl-2, 2'-di-N-butylcarbamate (S-2), (S)-1, 1'-bi-2-naphthyl-2-N-butylcarbamate-2'-butyrate (S-3), 2, 2'-biphenyl-di-N-butylcarbamate (4), 2, 2'-biphenyl-2-N-octadecylcarbamate-2'-N-octylcarbamate (5), 2, 2'-biphenyl-2-N-octadecylcarbamate-2'-N-phenylcarbamate (6), 2, 2'-biphenyl-2-N-butylcarbamate-2'-butyrate (7), 2, 2'-biphenyl-2-N-butylcarbamate-2'-ol (8), 2, 2'-biphenyl-2-N-octylcarbamate-2'-ol (9), (R)-1, 1'-bi-2-N-naphthyl-2-butylcarbamate-2'-ol (R-10), and glyceryl-1,2, 3-tri-N-butylcarbamate (11) are prepared and evaluated for their inhibition effects on porcine pancreatic cholesterol esterase. All inhibitors are irreversible inhibitors of the enzyme. Carbamates 1-3 and 7-10 are the first alkyl chain and esteratic binding site-directed irreversible inhibitors due to the fact that the reactivity of the enzyme is protected by the irreversible inhibitor, trifluoroacetophenone in the presence of these carbamates. Carbamate 1 is the least potent inhibitor for the enzyme probably due to the fact that the inhibitor molecule adopts a linear conformation and one of the carbamyl groups of the inhibitor molecule covalently interacts with the first alkyl chain binding site of the enzyme while the other carbamyl group of the inhibitor molecule exposes outside the active site. With near orthogonal conformations at the pivot bond of biaryl groups, one carbamyl group of carbamates S-2, S-3, and R-10 covalently binds to the first alkyl chain binding site of the enzyme while the other carbamyl, butyryl, or hydroxy group can not bind covalently to the second alkyl chain binding site probably due to the orthogonal conformations. Carbamates 4-9 and 11 are very potent inhibitors for the enzyme probably due to the fact that all these molecules freely rotate at the pivot bond of the biphenyl or glyceryl group and therefore can fit well into the bent-shaped first and second alkyl chains binding sites of the enzyme. Although, carbamates 4-6 and 11 are irreversible inhibitors of cholesterol esterase, the enzyme is not protected but further inhibited by trifluoroacetophenone in the presence of these carbamates. Therefore, carbamates 4-6 and 11 covalently bind to the first alkyl chain binding site of the enzyme by one of the carbamyl groups and may also bind to the second alkyl chain binding site of the enzyme by the second carbamyl group. Besides the bent-shaped conformation, the inhibition by carbamate 6 is probably assisted by a favorable pi-pi interaction between Phe 324 at the second alkyl chain binding site of the enzyme and the phenyl group of the inhibitor molecule. For cholesterol esterase, carbamates 8-10 are more potent than carbamates S-2, 4, and 5 probably due to the fact that the inhibitor molecules interact with the second alkyl chain binding site of the enzyme through a hydrogen bond between the phenol hydroxy group of the inhibitor molecules and the His 435 residue in that site.