Synthesis and antiviral activity of monobactams inhibiting the human cytomegalovirus protease

Monocyclic β-Lactam: A Review on Synthesis and Potential Biological Activities of a Multitarget Core

A monocyclic ring in their structure characterizes monobactams, a subclass of β-lactam antibiotics. Many of these compounds have a bactericidal mechanism of action and acts as penicillin and cephalosporins, interfering with bacterial cell wall biosynthesis. The synthesis of novel β-lactams is an emerging area of organic synthesis research due to the problem of increasing bacterial resistance to existing β -lactam antibiotics, and, in this way, new compounds have been presented with several structural modifications, aiming to improve biological activities. Among the biological activities studied, the most outstanding are antibacterial, antitubercular, anticholesterolemic, anticancer, antiinflammatory, antiviral, and anti-enzymatic, among others. This review explores the vast number of works related to monocyclic β-lactams, compounds of great importance in scientific research.

Diazocarbonyl derivatives of amino acids: unique chiral building blocks for the synthesis of biologically active compounds

This review deals with applications of chiral α-amino diazoketones, α-amino acid derivatives, in the synthesis of various biologically active compounds. General approaches to the synthesis of chiral α-amino diazoketones, including the Arndt – Eistert reaction, acylation of trimethylsilyldiazomethanes, etc., are discussed. Due to the presence of three functional groups, these building blocks can be used to produce a wide range of organic compounds with potential physiological activity, ranging from various heterocyclic compounds to peptidomimetics. Methods for the synthesis of β-amino acid-containing peptides and depsipeptides, amino acid derivatives and heterocyclic compounds with three- to seven-membered rings are considered.

The bibliography includes 226 references.

Optimization of a β-Lactam Scaffold for Antibacterial Activity via the Inhibition of Bacterial Type I Signal Peptidase

β-Lactam antibiotics, one of the most important class of human therapeutics, act via the inhibition of penicillin-binding proteins (PBPs). The unparalleled success in their development has inspired efforts to develop them as inhibitors of other targets. Bacterial type I signal peptidase is evolutionarily related to the PBPs, but the stereochemistry of its substrates and its catalytic mechanism suggest that β-lactams with the 5S stereochemistry, as opposed to the 5R stereochemistry of the traditional β-lactams, would be required for inhibition. We report the synthesis and evaluation of a variety of 5S penem derivatives and identify several with promising activity against both a Gram-positive and a Gram-negative bacterial pathogen. To our knowledge these are the first 5S β-lactams to possess significant antibacterial activity and the first β-lactams imparted with antibacterial activity via optimization of the inhibition of a target other than a PBP. Along with the privileged status of their scaffold and the promise of bacterial signal peptidase I (SPase) as a target, this activity makes these compounds promising leads for development as novel therapeutics.

The chemistry and biological potential of azetidin-2-ones

Azetidin-2-ones, commonly referred as β-lactams, represent a unique ring system, with interesting chemistry and great biological potential. Besides its well known antibiotic activity, this ring system exhibits a wide range of activities, attracting the attention of researchers. The biological and pharmacological profile of azetidin-2-ones is reviewed here comprehensively with several examples under fourteen different activity heads. The chemistry and methods of synthesis have also been discussed.

In vitro evaluation of the antielastase activity of polycyclic β-lactams

A series of bi- and tricyclic β-lactam compounds was synthesized and evaluated as inhibitors of cleavage of synthetic substrates in vitro by the serine proteases Human Leukocyte Elastase (HLE), Human Leukocyte Proteinase 3 (HLPR3) and Porcine Pancreatic Elastase (PPE). The obtained results have permitted us to describe a homobenzocarbacephem compound as HLE and HLPR3 inhibitor, to observe the positive effect that the styryl group exerts on the HLE inhibitory activity in polycyclic β-lactam compounds and to conclude that the hydroxyl function decreases the HLE inhibitory activity or rules it out completely.

2-Azetidinone--a new profile of various pharmacological activities

2-azetidinone, a β-lactam four member heterocyclic compound involved in research aimed to evaluate new products that possess interesting biological activities. These compounds reported for their antimicrobial and antifungal activities. Successful introduction of aztreonam as a potent inhibitor of cephalosporinase and ezetimibe as a cholesterol absorption inhibitor proved potential of 2-azetidinone moiety. Subsequently 2-azetidinones were highlighted as a potent mechanism based inhibitor of several enzymes like human tryptase, chymase, thrombin, leukocyte elastase, human cytomegalovirus protease and serine protease enzyme. These derivatives also known to possess antitubercular, anti-inflammatory, antitumor, anti-HIV, antiparkinsonian, antidiabetic and vasopressin V1a antagonist activity. The present review article focuses on the pharmacological profile of 2-azetidinones with their potential activities.

Mechanistic insights into the inhibition of prostate specific antigen by β-lactam class compounds

Prostate Specific Antigen (PSA) is a biomarker used in the diagnosis of prostate cancer and to monitor therapeutic response. However, its precise role in prostate carcinogenesis and metastasis remains largely unknown. A number of studies arguing in the favor of an active role of PSA in prostate cancer development and progression have implicated this serine protease in the release and activation of growth factors such as insulin-like growth factor 1 (IGF1) through cleavage of insulin like growth factor binding protein 3 and Transforming Growth Factor beta (TGF-beta) through cleavage of Latent TGF-beta. In contrast, other studies suggest that PSA activity might hinder tumor development and progression. In light of these contradictory findings, efficient inhibitors of PSA are needed for exploring its biological role in tumor development and metastasis. Towards the goal of developing potent inhibitors of PSA, we have explored the molecular mechanism of a series of beta-lactam based compounds on binding to PSA using activity assays, matrix assisted laser desorption ionization with a time-of-flight mass spectrometry, and GOLD docking methodology. The mass spectrometry experiments and the activity assays confirmed the time-dependent and covalent nature of beta-lactam binding. To gain insights on the reaction intermediates at the molecular level, we docked beta-lactam inhibitors to a homology modeled PSA using the GOLD docking program in noncovalent and covalent binding modes. The docking studies elucidated the molecular details of the early noncovalent Michaelis complex, the acyl-enzyme covalent complex, and the nature of conformational reorganization required for the long term stability of the covalent complex. Additionally, the molecular basis for the effect of stereochemistry of the lactam ring on the inhibitory potency was elucidated through docking of beta-lactam enantiomers. As a validation of our docking methodology, two novel enantiomers were synthesized and evaluated for their inhibitory potency using fluorogenic substrate based activity assays. Additionally, cis enantiomers of eight beta-lactam compounds reported in a previous study were docked and their GOLD scores and binding modes were analyzed in order to assess the general applicability of our docking results. The close agreement of our docking results with the experimental data validates the mechanistic insights revealed through the docking studies and paves the way for the design and development of potent and specific inhibitors of PSA.

Diastereoselective addition of chlorotitanium enolates of N-acyl thiazolidinethione to activated imines — A novel synthesis of β-lactams

We report a novel methodology for preparing enantiomerically pure β-lactams, starting from nitriles in diastereomeric ratios up to 10:1. The power of the methodology was demonstrated by the efficient synthesis of the cholesterol absorption inhibitor SCH 48462.Key words: β-lactam, N-metalloaldimine, titanium Lewis acids, cholesterol absorption inhibitor.

An ab Initio Study on the Allene−Isocyanic Acid and Ketene−Vinylimine [2 + 2] Cycloaddition Reaction Paths

The reaction paths of [2 + 2] cycloadditions of allene (H2C=C=CH2) to isocyanic acid (HN=C=O) and ketene (H2C=C=O) to vinylimine (H2C=C=NH), leading to all the possible 14 four-membered ring molecules, were investigated by the MP2/aug-cc-pVDZ method. In the two considered reactions, the 2-azetidinone (beta-lactam) ring compounds were predicted to be the most stable thermodynamically in the absence of an environment. Although 4-methylene-2-azetidinone is the most stable product of the ketene-vinylimine cycloaddition, its activation barrier is higher than that for 4-methylene-2-iminooxetane by ca. 6 kcal/mol. Therefore, the latter product can be obtained owing to kinetic control. The activation barriers in the allene-isocyanic acid reactions are quite high, 50-70 kcal/mol, whereas in the course of the ketene-vinylimine cycloaddition they are equal to ca. 30-55 kcal/mol. All the reactions studied were found to be concerted and mostly asynchronous. Simulation of the solvent environment (toluene, tetrahydrofuran, acetonitrile, and water) by using Tomasi's polarized continuum model with the integral equation formalism (IEF-PCM) method showed the allene-isocyanic reactions remained concerted, yet the activation barriers were somewhat higher than those in the gas phase, whereas the ketene-vinylimine reactions became stepwise. The larger the solvent dielectric constant, the lower the activation barriers found. The lowest-energy pathways in the gas phase and in solvent were confirmed by intrinsic reaction coordinate (IRC) calculations. The atoms in molecules (AIM) analysis of the electron density distribution in the transition-state (TS) structures allowed us to distinguish pericyclic from pseudopericyclic from nonplanar-pseudopericyclic types of reactions.

Synthesis of Strained Tricyclic β-Lactams by Intramolecular [2+2] Cycloaddition Reactions of 2-Azetidinone-Tethered Enallenols: Control of Regioselectivity by Selective Alkene Substitution

A convenient metal-free methodology for the preparation of structurally novel, strained tricyclic beta-lactams containing a cyclobutane ring has been developed. The first examples accounting for the intramolecular [2+2] cycloaddition reactions in beta-lactams have been achieved by the thermolysis of 2-azetidinone-tethered enallenols, which have been prepared in aqueous media by regio- and diastereoselective indium-mediated carbonyl allenylation of 4-oxoazetidine-2-carbaldehydes. Notably, the regioselectivity of the cycloaddition can be tuned in the allene component just by a subtle variation in the substitution pattern of the alkene component.

From 1-acyl-beta-lactam human cytomegalovirus protease inhibitors to 1-benzyloxycarbonylazetidines with improved antiviral activity. A straightforward approach to convert covalent to noncovalent inhibitors

Starting from the structure of known beta-lactam covalent human cytomegalovirus (HCMV) protease inhibitors and from the knowledge of the residues implicated in the active site of this enzyme, we designed a series of phenylalanine-derived 2-azetidinones bearing a 4-carboxylate moiety that could be apt for additional interactions with the guanidine group of the Arg165/Arg166 residues of the viral protease. Some compounds within this series showed anti-HCMV activity at 10-50 muM, but rather high toxicity. The presence of aromatic 1-acyl groups and a certain hydrophobic character in the region of the 4-carboxylate were stringent requirements for anti-HCMV activity. To go a step ahead into the search for effective HCMV medicines, we then envisaged a series of noncovalent inhibitors by simple deletion of the carbonyl group in the beta-lactam derivatives to provide the corresponding azetidines. This led to low micromolar inhibitors of HCMV replication, with 17 and 27 being particularly promising lead compounds for further investigation, although their toxicity still needs to be lowered.

Synthesis and anti-HCMV activity of 1-acyl-beta-lactams and 1-acylazetidines derived from phenylalanine

Different Phe-derived 1-acyl-beta-lactams, analogous to a series of 2-azetidinones acting as HCMV serine protease inhibitors, were synthesized. Some of these compounds were modest inhibitors of the HCMV replication. Interestingly, removal of the carbonyl group of the beta-lactam ring, most likely acting as the serine trap, resulted in an azetidine derivative with anti-HCMV activity comparable to that of the reference compound ganciclovir.

Conjugate Addition to 1-Phosphono-2-aza-1,3-butadienes: Synthesis of Phosphonylated γ-Lactams

Several 1-phosphono-2-aza-1,3-butadienes, 1 and 13-20, were evaluated in the reaction with different enolate-type nucleophiles to induce addition at the 1- or the 4-position of the azadiene. 1-Phosphono-2-azadienes 1 react with sodium malonate at the 1-position, leading to the formation of bisenamines 12 after elimination of the phosphonate moiety. On the contrary, sodium malonate adds at the 4-position of 1-aryl-1-phosphono-2-azadienes 14-19 when the azadienes bear a halogenated phenyl substituent, and the resulting addition products 21-26 are easily transformed into the corresponding phosphonylated gamma-lactams 35-40. The regioselectivity of the addition is explained by reversal of polarization of the azadiene due to the electron-withdrawing character of the halogenated phenyl substituents.

Studies on Stereoselective [2+2] Cycloadditions between N,N-Dialkylhydrazones and Ketenes

Staudinger-like cycloadditions between chiral, non-racemic N,N-dialkylhydrazones 1 and functionalized ketenes constitute an efficient methodology for the stereoselective construction of the beta-lactam ring. The potential for fine tuning of the dialkylamino auxiliary structure, the availability of a high-yielding deprotection method for the release of the free azetidinones, and the high thermal and chemical stability of hydrazones as N-dialkylamino imines are highlighted as the key elements for the success of the strategy. This last aspect is of particular importance concerning generality: even hydrazones from easily enolizable aldehydes or from formaldehyde reacted to afford the corresponding cycloadducts with high chemical and stereochemical yields. The syntheses of the beta-amino-alpha-hydroxyacids (2R,3S)-phenylisoserine (42) and (2R,3S)-norstatin (45) were accomplished as illustrative examples of the synthetic utility of this procedure. A model system for the cycloaddition of g series auxiliaries was studied by ab initio computational methods. The collected results support a two-step mechanism through zwitterionic intermediates, and explain the observed absolute and relative stereochemistry in terms of the preferred outward cycloaddition to the Re face of the hydrazone.

Studies toward the Total Synthesis of Wiedemannic Acid

[reaction: see text] We report a novel and efficient diastereoselective synthesis of wiedemannic acid analogue 30 in 16 steps from 7 using a tandem oxy-Cope/Claisen/ene reaction as the key step. Comparison of NMR data between wiedemannic acid (1) and analogue 30 leads us to believe that the reported stereochemistry at the ring junction of 1 is incorrect.

Advances in the catalytic, asymmetric synthesis of beta-lactams

In this Account, we illustrate our contribution to the catalytic, asymmetric synthesis of beta-lactams through a flexible [2 + 2] cycloaddition strategy. We also explore the scope of our methodology and comment on future directions.

1-Alkoxycarbonyl-3-halogenoazetidin-2-ones as elastase (PPE) inhibitors

A series of 1-alkoxycarbonyl-3-halogenoazetidin-2-ones, designed as potential suicide inhibitors of serine proteases, has been synthesized and evaluated against porcine pancreatic elastase (PPE). All the compounds were transient inhibitors, their activity depending mainly on the nature of the halogen substituent: bromo- and iodo- derivatives are more active (K(i) approximately 2-22 microM) than 3-chloroazetidinones (K(i) approximately 20-150 microM). The lipophilicity of the N-1 substituent appeared to exert a slightly positive effect.

The development of the first catalyzed reaction of ketenes and imines: catalytic, asymmetric synthesis of beta-lactams

We report practical methodology for the catalytic, asymmetric synthesis of beta-lactams resulting from the development of a catalyzed reaction of ketenes (or their derived zwitterionic enolates) and imines. The products of these asymmetric reactions can serve as precursors to a number of enzyme inhibitors and drug candidates as well as valuable synthetic intermediates. We present a detailed study of the mechanism of the beta-lactam forming reaction with proton sponge as the stoichiometric base, including kinetics and isotopic labeling studies. Stereochemical models based on molecular mechanics (MM) calculations are also presented to account for the observed stereoregular sense of induction in our reactions and to provide a guidepost for the design of other catalyst systems.

Strategies in the design of antiviral drugs

A decade ago, just five drugs were licensed for the treatment of viral infections. Since then, greater understanding of viral life cycles, prompted in particular by the need to combat human immunodeficiency virus, has resulted in the discovery and validation of several targets for therapeutic intervention. Consequently, the current antiviral repertoire now includes more than 30 drugs. But we still lack effective therapies for several viral infections, and established treatments are not always effective or well tolerated, highlighting the need for further refinement of antiviral drug design and development. Here, I describe the rationale behind current and future drug-based strategies for combating viral infections.

Recent strategies in the development of new human cytomegalovirus inhibitors

Human cytomegalovirus (HCMV) is one of the most common opportunistic infections in immunucompromised individuals, such as AIDS patients and organ transplant recipients, and is the most frequent congenital viral infection in humans. Despite a reduction of the incidence of AIDS-related opportunistic infections in patients under highly active antiretroviral treatment, attention should be paid to the HCMV risk factor in these individuals. Furthermore, HCMV may have an important role in atherosclerosis. Existing antiviral treatments for the HCMV infection suffer from poor bioavailability, toxicity, and limited effectiveness, mainly due to the development of drug resistance. Fortunately there are novel and potentially very effective new compounds undergoing pre-clinical and clinical evaluation. This review provides an overview in the last five years of new HCMV inhibitors (chemical structures, SAR, and new mechanisms of action) with the aim to provide new clues for the development of future drugs against this opportunistic virus.

A trans-stereoselective synthesis of 3-Halo-4-alkyl(aryl)-NH-azetidin-2-ones

[formula: see text] Conrotatory ring closure of 1-halo-3-aza-4-alkyl-1,3-dienes in refluxing toluene gives rise to 3-halo-4-aryl-2-azetidinones in satisfactory yields. Dehalogenation of the resulting beta-lactams by tris(trimethylsilyl)silane furnished 3-unsubstituted azetidinones, valuable intermediates in the synthesis of biologically active compounds.