Antibacterials. Synthesis and structure-activity studies of 3-aryl-2-oxooxazolidines. 1. The "B" group

Synthesis and in vitro activity of new methylenepiperidinyl and methylenepyrrolidinyl oxazolidinone antibacterial agents

We have prepared and evaluated the antibacterial activities of a series of substituted methylenepiperidinyl and methylenepyrrolidinyl oxazolidinones against several gram-positive strains including the resistant strains of Staphyloccus and Enterococcus, such as MRSA, CRSA, MSSA and VRE. Some of them showed comparable or superior in vitro activities (MIC) to vancomycin.

N6-cyclopentyl-2-(3-phenylaminocarbonyltriazene-1-yl)adenosine (TCPA), a very selective agonist with high affinity for the human adenosine A1 receptor

Four subtypes of adenosine receptors are currently known, that is, A(1), A(2A), A(2B), and A(3) receptors. Interestingly, quite substantial species differences exist especially between human and rat A(3) receptors. As a result, ligands such as CCPA, which are very selective for the rat A(1) receptor versus the human A(3) receptor, are substantially less selective when the human A(1) and A(3) receptors are compared. New 2-substituted and 2,N(6)-disubstituted adenosines were synthesized, and their affinities for the human adenosine A(1), A(2A), A(2B), and A(3) receptors were determined. Although large substituents on the C2-position are generally thought to yield adenosine A(2A) receptor selective ligands, the reported series of 2-triazeno-substituted adenosines had a very high affinity for the A(1) receptor. For example, 2-(3-phenylaminocarbonyltriazene-1-yl)adenosine had an affinity of 6.1 +/- 1.3 nM for the human adenosine A(1) receptor. Introduction of a diphenethyl substituent at the N(6)-position of this compound resulted in a high-affinity agonist, 3.1 +/- 0.9 nM, for the human adenosine A(1) receptor with 316- and 45-fold selectivity versus the human A(2A) and human A(3) receptors, respectively. The most selective, high-affinity human adenosine A(1) receptor agonist was the disubstituted compound N(6)-cyclopentyl-2-(3-phenylaminocarbonyltriazene-1-yl)adenosine (TCPA). TCPA had an affinity of 2.8 +/- 0.8 nM for the human adenosine A(1) receptor and was 75-fold and 214-fold selective versus the human A(2A) and human A(3) receptors, respectively. In addition, TCPA was a full agonist and inhibited the forskolin-induced cAMP production of CHO cells stably transfected with the human adenosine A(1) receptor with an IC(50) of 1.5 +/- 0.5 nM.

Highly efficient CuI-catalyzed coupling of aryl bromides with oxazolidinones using Buchwald's protocol: a short route to linezolid and toloxatone

[reaction: see text] Coupling of a variety of substituted aryl bromides with oxazolidinones has been achieved using the Buchwald protocol for the amidation of aryl halides. This procedure is exemplified by the synthesis of two medicinally important molecules, linezolid and toloxatone.

Identification of phenylisoxazolines as novel and viable antibacterial agents active against Gram-positive pathogens

A new and promising group of antibacterial agents, collectively known as the oxazolidinones and exemplified by linezolid (PNU-100766, marketed as Zyvox), have recently emerged as important new therapeutic agents for the treatment of infections caused by Gram-positive bacteria. Because of their significance, extensive synthetic investigations into the structure-activity relationships of the oxazolidinones have been conducted at Pharmacia. One facet of this research effort has focused on the identification of bioisosteric replacements for the usual oxazolidinone A-ring. In this paper we describe studies leading to the identification of antibacterial agents incorporating a novel isoxazoline A-ring surrogate. In a gratifying result, the initial isoxazoline analogue prepared was found to exhibit in vitro antibacterial activity approaching that of the corresponding oxazolidinone progenitor. The synthesis and antibacterial activity profile of a preliminary series of isoxazoline analogues incorporating either a C-C or N-C linkage between their B- and C-rings will be presented. Many of the analogues exhibited interesting levels of antibacterial activity. The piperazine derivative 54 displayed especially promising in vitro activity and in vivo efficacy comparable to the activity and efficacy of linezolid.

Novel stereoselective synthesis of functionalized oxazolidinones from chiral aziridines

Enantiomerically pure N-(R)-alpha-methylbenzyl-4(R)-(chloromethyl)oxazolidinones (4R)-5a-k were synthesized in one step and high yields from various aziridine-2-methanols (S)-2a-k by intramolecular cyclization with phosgene. The alpha-methylbenzyl substituent on the nitrogen was easily cleaved to give both enanatiomers of 4-(chloromethyl)oxazolidinones (R)-7a and (S)-7a. (R)-7a was used for the efficient syntheses of (L)-homophenylalaninol analogues (S)-12a-j. We also applied the same methodology to prepare oxazolidinones 9a-c containing a heteroatom-substituted alkyl group at C-4 in high yields.

A novel synthesis of 5-functionalized oxazolidin-2-ones from enantiomerically pure 2-substituted N-[(R)-(+)-alpha-methylbenzyl]aziridines

5-Funtionalized enantiomerically pure oxazolidin-2-ones were prepared in one pot from commercially available chiral aziridines bearing an electron-withdrawing group at C-2 with retention of the configuration in high yields by regioselective aziridine ring-opening followed by intramolecular cyclization.

Synthesis and antibacterial activity of 5-substituted oxazolidinones

A series of 5-substituted oxazolidinones with varying substitution at the 5-position of the oxazolidinone ring were synthesized and their in vitro antibacterial activity was evaluated. The compounds demonstrated potent to weak antibacterial activity. A novel compound (PH-027) demonstrated potent antibacterial activity, which is comparable to or better than those of linezolid and vancomycin against antibiotic-susceptible standard and clinically isolated resistant strains of gram-positive bacteria. Although the presence of the C-5-acetamidomethyl functionality at the C-5 position of the oxazolidinones has been widely claimed and reported as a structural requirement for optimal antimicrobial activity in the oxazolidinone class of compounds, our results from this work identified the C-5 triazole substitution as a new structural alternative for potent antibacterial activity in the oxazolidinone class.

Synthesis of conformationally constrained analogues of linezolid: structure-activity relationship (SAR) studies on selected novel tricyclic oxazolidinones

In an effort to discover potent antibacterials based on the entropically favored "bioactive conformation" approach, we have designed and synthesized a series of novel tricyclic molecules mimicking the conformationally constrained structure of the oxazolidinone antibacterial, Linezolid 1. The structure 3 obtained by this approach was synthesized and found to be moderately active against a panel of Gram-positive organisms tested. Further introduction of a fluorine atom in the aromatic ring of compound 3 as in Linezolid resulted in some excellent compounds possessing potent antibacterial activity. The thus obtained lead molecule 16 was further fine-tuned by structure-activity relationship studies on the amide functionality leading to a number of novel tricyclic oxazolidinone derivatives. Some particularly interesting compounds include the thioamides 36 and 37, thiocarbamate 41, and thiourea 45. The in vitro activity results of amide homologues of 16 (compounds 25-30) revealed that compounds up to four carbon atoms on the amide nitrogen retain the activity. In general, thioamides and thiocarbamates are more potent when compared to the corresponding amides and carbamates.

Novel piperidinyloxy oxazolidinone antibacterial agents. Diversification of the N-Substituent

Oxazolidinone antibacterial agents, where the morpholino group of linezolid was replaced with an N-substituted piperidinyloxy moiety, were synthesized and shown to be active against a variety of resistant and susceptible Gram-positive organisms. The functionality attached to the piperidine nitrogen was varied extensively to determine the SAR for this series. One of the most potent compounds, 11, showed in vivo efficacy upon subcutaneous administration in a Staphylococcus aureus Smith murine systemic infection.

Synthesis and antibacterial activity of linezolid analogues

Several new compounds of oxazolidinone class were designed and synthesized referring to the structure-activity relationship studies and the synthesis of Linezolid, and their antibacterial activity was studied.

Three-dimensional quantitative structure-activity relationship (3D-QSAR) of 3-aryloxazolidin-2-one antibacterials

Three-dimensional quantitative structure-activity relationship (3D-QSAR) studies for 3-aryloxazolidin-2-one antibacterials were performed using the genetic function approximation algorithm. This study was performed using 60 compounds, in which the QSAR models were developed using a training set of 50 compounds. The in vitro minimum inhibitory concentration (MIC) against Staphylococcus aureus SFCO-1a was used for the study. The predictive ability of the QSAR model was evaluated by using a test set of 10 compounds. The statistical quality of the QSAR models was assessed using statistical parameters r(2), r(2)(cv) (cross-validated r(2)), r(2)(pred) (predictive r(2)) and lack of fit measure (LOF). The results obtained indicate that the antibacterial activity of the 3-aryloxazolidin-2-ones is strongly dependent on electronic factor as expressed by lowest unoccupied molecular orbital energy (LUMO), spatial factor as expressed by density and thermodynamic factors accounted for by molar refractivity and heat of formation. The model is presently being used to design and predict new potent molecules prior to synthesis.

Polymer-aided stereodivergent synthesis (PASS): a new concept for the discrete preparation of optical antipodes

[structure: see text]. A new concept for the discrete preparation of optical antipodes is reported. The approach makes use of a cyclization/cleavage procedure that has been applied to polymer-supported quasi-meso compound 1, containing a polymeric leaving group and a regular leaving group. Two-directional cyclization leads to the formation and separation of quasi-enantiomers 2 and 3 simultaneously, with one being immobilized and one free in solution. Treatment of 2 and 3 with appropriate nucleophiles gives discrete enantiomers 4 and 5.

Structure-activity relationship (SAR) studies on oxazolidinone antibacterial agents. 3. Synthesis and evaluation of 5-thiocarbamate oxazolidinones

A series of 5-thiocarbamate oxazolidinones was prepared and tested for in vitro and in vivo antibacterial activities. The results of in vitro antibacterial activity indicated that the 5-thiocarbamate group was a suitable substituent for the activity by the 5-moderate hydrophilicity. The compounds within a favorable logP value range were found to have potent in vitro antibacterial activity against gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE). Compounds 3a and 4h were superior to linezolid in both in vitro and in vivo potency and were considered to be hopeful compounds. We also discuss the pharmacokinetic properties of several compounds in mice.

Structure-activity relationship (SAR) studies on oxazolidinone antibacterial agents. 2. Relationship between lipophilicity and antibacterial activity in 5-thiocarbonyl oxazolidinones

5-Thiourea and 5-dithiocarbamate oxazolidinones were synthesized as a continuation of research on 5-thiocarbonyl oxazolidinone antibacterial agents considering the hydrophobic parameters of the molecule. The structure-activity relationship (SAR) study revealed that the antibacterial activity on 5-thiocarbonyl oxazolidinones was significantly affected by the lipophilicity, especially the calculated log P value and the balance between 5-hydrophilic (or hydrophobic) substituent and hydrophobic (or hydrophilic) substituents on the benzene ring. Some of 5-thiocarbonyl oxazolidinones were found to have good in vitro antibacterial activity against gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE).

Structure-activity relationship (SAR) studies on oxazolidinone antibacterial agents. 1. Conversion of 5-substituent on oxazolidinone

A structure-activity relationship (SAR) study on 5-substituted oxazolidinones as an antibacterial agent is described. The oxazolidinones, of which 5-acetylaminomethyl moiety was converted into other functions, were prepared and evaluated for antibacterial activity. Elongation of the methylene chain (8) and conversion of the acetamido moiety into guanidino moiety (12) decreased the antibacterial activity. The replacement of carbonyl oxygen (=O) by thiocarbonyl sulfur (=S) enhanced in vitro antibacterial activity. Especially, compound 16, which had the 5-thiourea group, showed 4-8 stronger in vitro activity than linezolid. Our SAR study revealed that the antibacterial activity was greatly affected by the conversion of 5-substituent.

Facile synthesis of O6-alkyl-, O6-aryl-, and diaminopurine nucleosides from 2'-deoxyguanosine

The 3',5'-bis-O-TBDMS derivative of 2'-deoxyguanosine can be converted to its O6-alkyl and O6-aryl ethers as well as to N6-substituted diaminopurine nucleosides in two simple steps. Also described is a novel, nonaqueous, one-step O6-desulfonylation method that leads to deprotection of the carbonyl moiety of 2'-deoxyguanosine.

N-[4-(1,1'-biphenyl)methyl]-4-(4-thiomorpholinylmethyl) benzenamines as non-oxazolidinone analogues of antimycobacterial U-100480

Thiomorpholine analogues of U-100480 with the biphenylmethyl group replacing the acetamidomethyloxazolidinone moiety have been synthesized and tested as antimycobacterial agents together with various related derivatives. Some biphenyl derivatives were endowed with high activity against Mycobacterium tuberculosis and other non-tuberculous mycobacteria.

Synthesis and antibacterial activity of [6,5,5] and [6,6,5] tricyclic fused oxazolidinones

A series of conformationally restricted, [6,5,5] and [6,6,5] tricyclic fused oxazolidinones were synthesized and tested for antibacterial activity. Several compounds in the trans-[6,5,5] series demonstrated potent in vitro and in vivo activity. This work provides valuable information regarding the preferred conformational orientation of the oxazolidinones at the binding site.

Separation of diastereoisomers of DuP 105, a novel oxazolidinone antibacterial agent, by supercritical fluid chromatography on a Chiralcel OD column

Oxazolidinones are a novel class of synthetic, orally-active antibacterial agents. DuP 105, which is representative of this class of compounds, is synthesized as a racemic mixture of two diastereoisomers. To ensure lot-to-lot consistency, separation and quantitation of these diastereoisomers is essential. Separation by reverse phase LC has not been achieved. This paper presents a supercritical fluid chromatography method using a Chiralcel OD column to resolve these diastereoisomers. A retention mechanism is briefly elaborated, based on the effects of temperature, pressure, percent modifier and type of modifier on resolution.

Synthesis and antibacterial activity of U-100592 and U-100766, two oxazolidinone antibacterial agents for the potential treatment of multidrug-resistant gram-positive bacterial infections

Bacterial resistance development has become a very serious clinical problem for many classes of antibiotics. The 3-aryl-2-oxazolidinones are a relatively new class of synthetic antibacterial agents, having a new mechanism of action which involves very early inhibition of bacterial protein synthesis. We have prepared two potent, synthetic oxazolidinones, U-100592 and U-100766, which are currently in clinical development for the treatment of serious multidrug-resistant Gram-positive bacterial infections caused by strains of staphylococci, streptococci, and enterococci. The in vitro and in vivo (po and iv) activities of U-100592 and U-100766 against representative strains are similar to those of vancomycin. U-100592 and U-100766 demonstrate potent in vitro activity against Mycobacterium tuberculosis. A novel and practical asymmetric synthesis of (5S)-(acetamidomethyl)-2-oxazolidinones has been developed and is employed for the synthesis of U-100592 and U-100766. This involves the reaction of N-lithioarylcarbamates with (R)-glycidyl butyrate, resulting in excellent yields and high enantiomeric purity of the intermediate (R)-5-(hydroxymethyl)-2-oxazolidinones.

Identification of a novel oxazolidinone (U-100480) with potent antimycobacterial activity

During the course of our investigations in the oxazolidinone antibacterial agent area, we have identified a subclass with especially potent in vitro activity against mycobacteria. The salient structural feature of these oxazolidinone analogues, 6 (U-100480), 7 (U-101603), and 8 (U-101244), is their appended thiomorpholine moiety. The rational design, synthesis, and evaluation of the in vitro antimycobacterial activity of these analogues is described. Potent activity against a screening strain of Mycobacterium tuberculosis was demonstrated by 6 and 7 (minimum inhibitory concentrations or MIC's < or = 0.125 micrograms/mL). Oxazolidinones 6 and 8 exhibit MIC90 values of 0.50 micrograms/mL or less against a panel of organisms consisting of five drug-sensitive and five multidrug-resistant strains of M. tuberculosis, with 6 being the most active congener. Potent in vitro activity against other mycobacterial species was also demonstrated by 6. For example, 6 exhibited excellent in vitro activity against multiple clinical isolates of Mycobacterium avium complex (MIC's = 0.5-4 micrograms/mL). Orally administered 6 displays in vivo efficacy against M. tuberculosis and M. avium similar to that of clinical comparators isoniazid and azithromycin, respectively. Consideration of these factors, along with a favorable pharmaco-kinetic and chronic toxicity profile in rats, suggests that 6 (U-100480) is a promising antimycobacterial agent.

4-(Aminomethyl)-1-aryl-2-pyrrolidinones, a new class of monoamine oxidase B inactivators

Both 4-(aminomethyl)-1-phenyl-2-pyrrolidinone (4a) and 4-(aminomethyl)-1- (methoxyphenyl)-2-pyrrolidinone (4b) hydrochlorides were synthesized via a six-step sequence, which represents a general approach to 1,4-disubstituted 2-pyrrolidinones. Both of these compounds inactivated monoamine oxidase B and represent the first in a new class of monomamine oxidase inactivators.