Antibacterials. synthesis and structure-activity studies of 3-aryl-2-oxooxazolidines. 4. Multiply-substituted aryl derivatives

Recent advances in the exploration of oxazolidinone scaffolds from compound development to antibacterial agents and other bioactivities

Bacterial infections cause a variety of life-threatening diseases, and the continuous evolution of drug-resistant bacteria poses an increasing threat to current antimicrobial regimens. Gram-positive bacteria (GPB) have a wide range of genetic capabilities that allow them to adapt to and develop resistance to practically all existing antibiotics. Oxazolidinones, a class of potent bacterial protein synthesis inhibitors with a unique mechanism of action involving inhibition of bacterial ribosomal translation, has emerged as the antibiotics of choice for the treatment of drug-resistant GPB infections. In this review, we discussed the oxazolidinone antibiotics that are currently on the market and in clinical development, as well as an updated synopsis of current advances on their analogues, with an emphasis on innovative strategies for structural optimization of linezolid, structure-activity relationship (SAR), and safety properties. We also discussed recent efforts aimed at extending the activity of oxazolidinones to gram-negative bacteria (GNB), antitumor, and coagulation factor Xa. Oxazolidinone antibiotics can accumulate in GNB by a conjugation to siderophore-mediated β-lactamase-triggered release, making them effective against GNB.

Microwave-Assisted Electrostatically Enhanced Phenol-Catalyzed Synthesis of Oxazolidinones

An electrostatically enhanced phenol is utilized as a straightforward, sustainable, and potent one-component organocatalyst for the atom-economic transformation of epoxides to oxazolidinones under microwave irradiation. Integrating a positively charged center into phenols over a modular one-step preparation gives rise to a bifunctional system with improved acidity and activity, competent in rapid assembly of epoxides and isocyanates under microwave irradiation in a short reaction time (20-60 min). A careful assessment of the efficacy of various positively charged phenols and anilines and the impact of several factors, such as catalyst loading, temperature, and the kind of nucleophile, on catalytic reactivity were examined. Under neat conditions, this one-component catalytic platform was exploited to prepare more than 40 examples of oxazolidinones from a variety of aryl- and alkyl-substituted epoxides and isocyanates within minutes, where up to 96% yield and high degree of selectivity were attained. DFT calculations to achieve reaction barriers for different catalytic routes were conducted to provide mechanistic understanding and corroborated the experimental findings in which concurrent epoxide ring-opening and isocyanate incorporation were proposed.

Recent Advances in the Rational Design and Optimization of Antibacterial Agents

This review discusses next-generation antibacterial agents developed using rational, or targeted, drug design strategies. The focus of this review is on small-molecule compounds that have been designed to bypass developing bacterial resistance, improve the antibacterial spectrum of activity, and/or to optimize other properties, including physicochemical and pharmacokinetic properties. Agents are discussed that affect known antibacterial targets, such as the bacterial ribosome, nucleic acid binding proteins, and proteins involved in cell-wall biosynthesis; as well as some affecting novel bacterial targets which do not have currently marketed agents. The discussion of the agents focuses on the rational design strategies employed and the synthetic medicinal chemistry and structure-based design techniques utilized by the scientists involved in the discoveries, including such methods as ligand- and structure-based strategies, structure-activity relationship (SAR) expansion strategies, and novel synthetic organic chemistry methods. As such, the discussion is limited to small-molecule therapeutics that have confirmed macromolecular targets and encompasses only a fraction of all antibacterial agents recently approved or in late-stage clinical trials. The antibacterial agents selected have been recently approved for use on the U.S. or European markets or have shown promising results in phase 2 or phase 3 U.S.

CLINICAL TRIALS

Effective in silico prediction of new oxazolidinone antibiotics: force field simulations of the antibiotic-ribosome complex supervised by experiment and electronic structure methods

We propose several new and promising antibacterial agents for the treatment of serious Gram-positive infections. Our predictions rely on force field simulations, supervised by first principle calculations and available experimental data. Different force fields were tested in order to reproduce linezolid's conformational space in terms of a) the isolated and b) the ribosomal bound state. In a first step, an all-atom model of the bacterial ribosome consisting of nearly 1600 atoms was constructed and evaluated. The conformational space of 30 different ribosomal/oxazolidinone complexes was scanned by stochastic methods, followed by an evaluation of their enthalpic penalties or rewards and the mechanical strengths of the relevant hydrogen bonds (relaxed force constants; compliance constants). The protocol was able to reproduce the experimentally known enantioselectivity favoring the S-enantiomer. In a second step, the experimentally known MIC values of eight linezolid analogues were used in order to crosscheck the robustness of our model. In a final step, this benchmarking led to the prediction of several new and promising lead compounds. Synthesis and biological evaluation of the new compounds are on the way.

An Efficient Amide-Aldehyde-Alkene Condensation: Synthesis for the N-Allyl Amides

The allylamine skeleton represents a significant class of biologically active nitrogen compounds that are found in various natural products and drugs with well-recognized pharmacological properties. In this personal account, we will briefly discuss the synthesis of allylamine skeletons. We will focus on showing a general protocol for Lewis acid-catalyzed N-allylation of electron-poor N-heterocyclic amides and sulfonamide via an amide-aldehyde-alkene condensation reaction. The substrate scope with respect to N-heterocyclic amides, aldehydes, and alkenes will be discussed. This method is also capable of preparing the Naftifine motif from N-methyl-1-naphthamide or methyl (naphthalene-1-ylmethyl)carbamate, with paraformaldehyde and styrene in a one-pot manner.

Determinants of the species selectivity of oxazolidinone antibiotics targeting the large ribosomal subunit

Oxazolidinone antibiotics bind to the highly conserved peptidyl transferase center in the ribosome. For developing selective antibiotics, a profound understanding of the selectivity determinants is required. We have performed for the first time technically challenging molecular dynamics simulations in combination with molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) free energy calculations of the oxazolidinones linezolid and radezolid bound to the large ribosomal subunits of the eubacterium Deinococcus radiodurans and the archaeon Haloarcula marismortui. A remarkably good agreement of the computed relative binding free energy with selectivity data available from experiment for linezolid is found. On an atomic level, the analyses reveal an intricate interplay of structural, energetic, and dynamic determinants of the species selectivity of oxazolidinone antibiotics: A structural decomposition of free energy components identifies influences that originate from first and second shell nucleotides of the binding sites and lead to (opposing) contributions from interaction energies, solvation, and entropic factors. These findings add another layer of complexity to the current knowledge on structure-activity relationships of oxazolidinones binding to the ribosome and suggest that selectivity analyses solely based on structural information and qualitative arguments on interactions may not reach far enough. The computational analyses presented here should be of sufficient accuracy to fill this gap.

Structure and properties of metal complexes of a pyridine based oxazolidinone synthesized by atmospheric CO2 fixation

Copper, platinum and palladium complexes of an oxazolidinone ligand show potential in catalysis or cytotoxicity, depending on the metal incorporated.

Investigational antimicrobial agents of 2013

New antimicrobial agents are always needed to counteract the resistant pathogens that continue to be selected by current therapeutic regimens. This review provides a survey of known antimicrobial agents that were currently in clinical development in the fall of 2012 and spring of 2013. Data were collected from published literature primarily from 2010 to 2012, meeting abstracts (2011 to 2012), government websites, and company websites when appropriate. Compared to what was reported in previous surveys, a surprising number of new agents are currently in company pipelines, particularly in phase 3 clinical development. Familiar antibacterial classes of the quinolones, tetracyclines, oxazolidinones, glycopeptides, and cephalosporins are represented by entities with enhanced antimicrobial or pharmacological properties. More importantly, compounds of novel chemical structures targeting bacterial pathways not previously exploited are under development. Some of the most promising compounds include novel β-lactamase inhibitor combinations that target many multidrug-resistant Gram-negative bacteria, a critical medical need. Although new antimicrobial agents will continue to be needed to address increasing antibiotic resistance, there are novel agents in development to tackle at least some of the more worrisome pathogens in the current nosocomial setting.

The oxazolidinones: past, present, and future

The success of linezolid stimulated significant efforts to discover new agents in the oxazolidinone class. Over a dozen oxazolidinones have reached the clinic, but many were discontinued due to lack of differentiated potency, inadequate pharmacokinetics, and safety risks that included myelosuppression. Four oxazolidinones are currently undergoing clinical evaluation. The Trius Therapeutics compound tedizolid phosphate (formerly known as torezolid phosphate, TR-701, DA-7218), the most advanced, is in phase 3 clinical trials for acute bacterial skin and skin structure infections. Rib-X completed two phase 2 studies for radezolid (Rx-01_667, RX-1741) in uncomplicated skin and skin structure infections and community-acquired pneumonia. Pfizer and AstraZeneca have each identified antitubercular compounds that have completed phase 1 studies: sutezolid (PNU-100480, PF-02341272) and AZD5847 (AZD2563), respectively. The oxazolidinones share a relatively low frequency of resistance largely due to the requirement of mutations in 23S ribosomal RNA genes. However, maintaining potency against strains carrying the mobile cfr gene poses a challenge for the oxazolidinone class, as well as other 50S ribosome inhibitors that target the peptidyl transferase center.

A critical review of oxazolidinones: an alternative or replacement for glycopeptides and streptogramins?

OBJECTIVE

To review the available data on the oxazolidinones linezolid and eperezolid.

DATA SELECTION

Published reports were obtained by searching MEDLINE for articles published between 1992 and 2000, inclusive. References of published papers were also obtained and reviewed. Abstracts from scientific proceedings were reviewed.

DATA EXTRACTION

Due to the limited data available regarding these agents, the criteria for study inclusion were not restrictive.

DATA SYNTHESIS

The oxazolidinones (eg, linezolid) are a new antimicrobial class with a unique mechanism of action. They are active against resistant Gram-positive cocci including methicillin-susceptible and -resistant Staphylococcus aureus (MRSA), methicillin-susceptible and -resistant Staphylococccus epidermidis, vancomycin-resistant enterococci (VRE) and penicillin-resistant Streptococcus pneumoniae (PRSP). Linezolid is active against anaerobes and displays modest activity against fastidious Gram-negative pathogens such as Haemophilus influenzae, but is not active against Enterobacteriaceae. Linezolid is available both orally and parenterally, and has a bioavailability of 100%. Clinical trials comparing linezolid with standard therapy have demonstrated similar bacteriological and clinical cures rates to standard therapy in community- and hospital-acquired pneumonia, uncomplicated and complicated skin and soft tissue infections, and infections caused by MRSA and VRE. Adverse effects have been minor and infrequent; however, platelets should be monitored in patients who have received more than two weeks of linezolid therapy. It is expected that these agents will have a bright future due to their excellent spectrum of activity against antibiotic-resistant Gram-positive organisms, such as MRSA, VRE and PRSP, and their excellent bioavailability.

CONCLUSION

The oxazolidinones represent a new class of antimicrobials with a unique mechanism of action. They have excellent activity against susceptible and resistant Gram-positive organisms such as MRSA, methicillin-susceptible S epidermidis, VRE and PRSP, and a good adverse effect profile; they can be administered both intravenously and orally. Their potential use in Canada may be as an intravenous and oral alternative to glycopeptides and streptogramins.

Focusing on new monoamine oxidase inhibitors

IMPORTANCE OF THE FIELD

Monoamine oxidase (MAO) plays a significant role in the control of intracellular concentration of monoaminergic neurotransmitters or neuromodulators and dietary amines. The rapid degradation of these molecules ensures the proper functioning of synaptic neurotransmission and is critically important for the regulation of emotional and other brain functions. Furthermore, modulators of neurotransmitters exert pleiotropic effects on mental and cognitive functions. The by-products of MAO-mediated reactions include several chemical species with neurotoxic potential. It is widely speculated that prolonged or excessive activity of these enzymes may be conducive to mitochondrial damages and neurodegenerative disturbances. In keeping with these premises, the development of human MAO inhibitors has led to important breakthroughs in the therapy of several neuropsychiatric disorders.

AREAS COVERED IN THIS REVIEW

This review highlights the recent MAO inhibitors related patents published from July 2005 to December 2009. It also reports on new associations of already known MAO inhibitors with other drugs, innovative therapeutic targets, MAO inhibitors obtained by plants extraction, alternative administration routes and synthetic processes.

WHAT THE READER WILL GAIN

The reader will gain an overview of the main structures being investigated and their biological activities.

TAKE HOME MESSAGE

Several of these MAO inhibitors appear promising for further clinical development.

Structure-activity relationships of diverse oxazolidinones for linezolid-resistant Staphylococcus aureus strains possessing the cfr methyltransferase gene or ribosomal mutations

Staphylococcal resistance to linezolid (LZD) is mediated through ribosomal mutations (23S rRNA or ribosomal proteins L3 and L4) or through methylation of 23S rRNA by the horizontally transferred Cfr methyltransferase. To investigate the structural basis for oxazolidinone activity against LZD-resistant (LZD(r)) strains, we compared structurally diverse, clinically relevant oxazolidinones, including LZD, radezolid (RX-1741), TR-700 (torezolid), and a set of TR-700 analogs (including novel CD-rings and various A-ring C-5 substituents), against a panel of laboratory-derived and clinical LZD(r) Staphylococcus aureus strains possessing a variety of resistance mechanisms. Potency against all strains was correlated with optimization of C- and D-rings, which interact with more highly conserved regions of the peptidyl transferase center binding site. Activity against cfr strains was retained with either hydroxymethyl or 1,2,3-triazole C-5 groups but was reduced by 2- to 8-fold in compounds with acetamide substituents. LZD, which possesses a C-5 acetamide group and lacks a D-ring substituent, demonstrated the lowest potency against all strains tested, particularly against cfr strains. These data reveal key features contributing to oxazolidinone activity and highlight structural tradeoffs between potency against susceptible strains and potency against strains with various resistance mechanisms.

Synthesis and antibacterial activity of substituted oxotriazolylphenyl oxazolidinones

A series of 3-(4'-(2''-alkyl-3''-oxy-1'',2'',4''-triazolyl)-phenyl)-5-substituted oxazolidinones was designed and synthesized for in vitro antibacterial activity testing against fourteen Gram-negative and six Gram-positive standard organisms. The minimum inhibitory concentration (MIC) was determined by agar dilution at concentrations of 0.10, 0.20, 0.39, 0.78, 1.56, 3.13, 6.25 microg/mL. Different alkyl groups at the 2''-position played an important role in the activity against Gram-positive organisms. (S)-3-(4'-(2''-ethyl-3''-oxy-1'',2'',4''-triazolyl)-phenyl)-5-acetamidomethyloxazolidinone was active against Staphylococcus epidermidis, Streptococcus pneumoniae, Streptococcus enteridis and Streptococcus nonhemolyticus, whereas 2''-methyl, 2''-propyl and 2''-n-butyl counterparts did not show activity at 6.25 microg/mL. Modification of the 5-substitutent of oxazolidinones also affected the activity against Gram-positive organisms. (S)-3-(4'-(2''-ethyl-3''-oxy-1'',2'',4''-triazolyl)-phenyl)-5-acetamidomethyloxazolidinones was approximately two fold more potent than 5-chloroacetamido, 5-dichloroacetamido and 5-trifluoroacetamido counterparts against Streptococcus enteridis. None of these compounds showed growth inhibition against fourteen Gram-negative organisms at 6.25 microg/mL.

New oxazolidinones

Due to the emergence of resistance to known antibiotics to various organisms, for example, Staphylococcus, Streptococcus, Enterococci, and Pseudomonas there is a renewed interest in the discovery of new antibacterials. Oxazolidinones, totally synthetic class of novel antibacterials, possess activity against drug-resistant Gram-positive pathogens, especially MRSA. Linezolid, the first approved drug from this class, has shown a great promise in saving lives of many patients by acting against drug-resistant Gram-positive organisms. However, its use is somewhat limited because of its myelotoxicity when used long term (>21 days). Various research groups are active in this area either to improve myelotoxicity profile of linezolid or to expand the spectrum of activity of linezolid. In spite of active research in this area, the discovery of an oxazolidinone possessing improved myelotoxicity compared to linezolid, linezolid-like efficacy, and PK remains challenging.

Preferential intramolecular ring closure of aminoalcohols with diethyl carbonate to oxazolidinones

The closure by cyclization with diethyl carbonate (EtO)(2)CO from aminoalcohols 1 as starting material can lead to the oxazolidinones 2a, b and 2c, respectively. In the reaction of trans-isomer (6) and (EtO)(2)CO, isolated products were also only 5-membered oxazolidinone derivative (7), containing its dehydrated derivative 8. The preferential formation of the 5-membered oxazolidinone ring system apparently indicated that this process (5-Exo-Trig ring closure) is more favorable than that of 6- or 7-membered ring derivative (3 or 9) by 6- or 7-Exo-Trig ring closure.

Synthesis, SAR and antibacterial studies on novel chalcone oxazolidinone hybrids

With an intention to synergise the antibacterial activity of chalcones and oxazolidinones, several hybrid compounds possessing both chalcone and oxazolidinone moieties were synthesized and tested for antibacterial activity. The hybrid molecules containing heterocycles instead of aromatic ring were found to be active. A SAR study with various heterocycles resulted in a lead molecule 20, which was converted to one of the potent antibacterial compounds 27.

Synthesis and In Vitro Evaluation of Substituted Phenyl-Piperazinyl-Phenyl Oxazolidinones Against Gram-positive Bacteria

With the incidence of linezolid-resistant Enterococcus faecalis, E. faecium and Staphylococcus aureus, modification of linezolid at the 5- and/or 3-positions led to the development of a series of 3-(methoxyl-phenyl)-piperazinyl-phenyl oxazolidinone analogues. These compounds were tested in vitro against six gram-positive standard organisms (S. aureus, S. epidermidis, S. pneumoniae, S. albus, Streptococcus enteridis and S. nonhemolyticus). 5-acetylaminomethyl oxazolidinones bearing fluorine at 3'-position of phenyl ring showed activities against several gram-positive bacteria (MIC: 3.13-6.25 mug/mL). The position of methoxyl group on the phenyl ring of piperazine group affected antibacterial spectrum. 3-(4'- (para-methoxyl-phenyl)-piperazinyl)-(3'-fluoro)-phenyl-5-acetylaminomethyl oxazolidinone was found active against 5 gram-positive organisms except S. nonhemolyticus, whereas 3-(4'-(ortho-methoxyl-phenyl)-piperazinyl)-(3'-fluoro)-phenyl-5-acetylaminomethyl oxazolidinone was found active only against 2 gram-positive organisms, namely S. albus, S. enteridis.