Inhibition of Human Cytomegalovirus Protease by Monocyclic β-Lactam Derivatives: Kinetic Characterization Using a Fluorescent Probe

Peptide-to-Small Molecule: Discovery of Non-Covalent, Active-Site Inhibitors of β-Herpesvirus Proteases

Viral proteases, the key enzymes that regulate viral replication and assembly, are promising targets for antiviral drug discovery. Herpesvirus proteases are enzymes with no crystallographically confirmed noncovalent active-site binders, owing to their shallow and polar substrate-binding pockets. Here, we applied our previously reported "Peptide-to-Small Molecule" strategy to generate novel inhibitors of β-herpesvirus proteases. Rapid selection with a display technology was used to identify macrocyclic peptide 1 bound to the active site of human cytomegalovirus protease (HCMVPro) with high affinity, and pharmacophore queries were defined based on the results of subsequent intermolecular interaction analyses. Membrane-permeable small molecule 19, designed de novo according to this hypothesis, exhibited enzyme inhibitory activity (IC50 = 10-6 to 10-7 M) against β-herpesvirus proteases, and the design concept was proved by X-ray cocrystal analysis.

Design, synthesis and cytotoxic evaluation of peptoid analogs of an anticancer active triazolylpeptidyl penicillin

Aim: Encouraged by the antitumor activity exhibited by triazolylpeptidyl penicillins, we decided to synthesize and evaluate a library of peptoid analogs. Results: The replacement of the dipeptide unit of the reference compound, TAP7f, was investigated. In addition, the effect of the triazole linking group on the biological activity of these new derivatives was evaluated, exchanging it with a glycine spacer. The cytotoxic effect of the library compounds was determined in the B16-F0 cell line and compared with the effects on normal murine mammary gland cells. Conclusion: Among the tested compounds, peptoid 4e exhibited the highest antiproliferative activity.

MetA (Rv3341) from Mycobacterium tuberculosis H37Rv strain exhibits substrate dependent dual role of transferase and hydrolase activity

The metA (Rv3341) gene from Mycobacterium tuberculosis H37Rv strain encodes a homoserine-acetyltransferase (HAT) enzyme, also called MetA. This enzyme plays a key role in the biosynthetic pathway of methionine and is a potential target for the development of antimicrobial drugs. Purified MetA showed 40 kDa molecular mass on SDS-PAGE. Manual docking was performed with substrates acetyl-CoA, l-homoserine, and p-nitrophenylacetate using crystal structure coordinates of MetA (PDB ID 6PUX) from M. tuberculosis. Multiple sequence alignment indicated that catalytic triad residues Ser157, Asp320, His350 were conserved across species in acetyltransferases, esterases, and hydrolases. As a conserved pentapeptide, GXSMG belongs to α/β hydrolase superfamily and it shares similarity with esterases and hydrolases from different sources. Hydrolase activity of MetA was tested using (PNPA), N-acetylglycine, N-acetylmethionine and Phe-Gly as substrate. LC-MS confirmed that MetA possessed HAT activity, but no homoserine-succinyltransferase (HST) and serine-acetyltransferase (SAT) activities. Replacing acetyl-CoA with PNPA as acetyl group donor showed a drastic reduction in transferase activity, arising due to the interaction of R227 of the enzyme with PNPA. This could prevent the binding of the second substrate in the right orientation and results in the preferential transfer of the acetyl group to water, thus exhibiting hydrolase rather than transferase activity. In this paper, we report that MetA has both transferase and hydrolase activity depending on the correct orientation of the second substrate and the availability of the amino acids involved in enzyme-substrate interaction.

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.

Chemoenzymatic Approach toward the Synthesis of 3-O-(α/β)-Glucosylated 3-Hydroxy-β-lactams

Glycosylation significantly alters the biological and physicochemical properties of small molecules. β-Lactam alcohols comprise eligible substrates for such a transformation based on their distinct relevance in the chemical and medicinal community. In this framework, the unprecedented enzymatic glycosylation of the rigid and highly strained four-membered β-lactam azaheterocycle was studied. For this purpose, cis-3-hydroxy-β-lactams were efficiently prepared in three steps by means of a classical organic synthesis approach, while a biocatalytic step was implemented for the selective formation of the corresponding 3-O-α- and -β-glucosides, hence overcoming the complexities typically encountered in synthetic glycochemistry and contributing to the increasing demand for sustainable processes in the framework of green chemistry. Two carbohydrate-active enzymes were selected based on their broad acceptor specificity and subsequently applied for the α- or β-selective formation of β-lactam-sugar adducts, using sucrose as a glucosyl donor.

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.

Synthesis and SAR studies on azetidine-containing dipeptides as HCMV inhibitors

SAR studies on an azetidine-containing dipeptide prototype inhibitor of HCMV are described. Three series of structurally modified analogues, involving substitutions at the N- and C-terminus, and at the C-terminal side-chain were synthesized and evaluated for antiviral activity. Aliphatic or no substituents at the C-carboxamide group, an aliphatic C-terminal side-chain, as well as a benzyloxycarbonyl moiety at the N-terminus were absolute requirements for anti-HCMV activity. The conformational restriction induced by the 2-azetidine residue into the dipeptide derivatives, identified by ¹H NMR as a γ-type reverse turn, seems to have influence on the activity of these molecules.

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.

Unexpected Four-Membered over Six-Membered Ring Formation during the Synthesis of Azaheterocyclic Phosphonates: Experimental and Theoretical Evaluation

The cyclization of functionalized aminophosphonates is studied on both experimental and theoretical grounds. In a recently described route to phosphono-beta-lactams [Stevens C. V.; Vekemans, W.; Moonen, K.; Rammeloo, T. Tetrahedron Lett. 2003, 44, 1619], it was found that starting from an ambident allylic anion only four-membered rings were formed without any trace of six-membered lactams. New anion trapping experiments revealed that the gamma-anion is highly reactive in intermolecular reactions. Ab initio calculations predict higher reaction barriers for the gamma-anion due to restricted rotation about the C-N bond and due to highly strained transition states during ring closure. The sodium or lithium counterion, explicit dimethyl ether solvent molecules, and bulk solvent effects were properly taken into account at various levels of theory.

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.

Stereocontrolled synthesis of anticancer β-lactams via the Staudinger reaction

Stereocontrolled synthesis of novel beta-lactams using polyaromatic imines following the Staudinger reaction has been accomplished. The effects of domestic microwave irradiation on this type of reaction have been investigated. Formation of trans-beta-lactams has been explained through isomerization of the enolates formed during the reaction of acid chloride (equivalent) with imines in the presence of triethylamine. A donor-acceptor complex pathway is believed to be involved in the formation of cis-beta-lactams. The effect of a peri hydrogen has been found to be significant in controlling the stereochemistry of the resulting beta-lactams. SAR has identified beta-lactams with anticancer activity. The presence of an acetoxy group has proven obligatory for their anticancer activity.

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.

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.