Indium-Mediated Selective Introduction of a 1,3-Butadien-2-yl Group at the C4-Position in 2-Azetidinones and Application of 1,3-Diene-Tethered 2-Azetidinones in the Diels–Alder Reaction

The reaction of 4-acetoxy-2-azetidinones with organoindium reagents generated in situ from indium and 1,4-dibromo-2-butyne in the presence of LiCl in DMF selectively produced 2-azetidinones which contain a 1,3-butadienyl-2-yl group at the C4-position in good yields. The Diels-Alder reaction of 4-[(1-methylene)prop-2-enyl]-2-azetidinones with a variety of dienophiles provided 2-azetidinones with valuable functional-group-substituted six-membered rings at the C4-position in good yields.

Synthesis of novel N-(4-ethoxyphenyl) azetidin-2-ones and their oxidative N-deprotection by ceric ammonium nitrate

It is shown that the N-(p-ethoxyphenyl) group on beta-lactams can be oxidatively removed by ceric ammonium nitrate in good yield. Fourteen new N-(p-ethoxyphenyl)-2-azetidinones 8a-n were synthesized through standard [2+2] ketene-imine cycloadditions (Staudinger reaction). Treatment of these compounds with ceric ammonium nitrate yielded the N-dearylated 2-azetidinones 9a-n in good to excellent yields. The effects of solvent, molar equiv of CAN and different temperatures have been investigated and optimum conditions were established.

Convenient synthesis of trans-beta-amino carboxylic esters with an azetidine skeleton via rearrangement of beta,gamma-aziridino alpha-amino esters

A short and facile approach to biologically interesting N-protected alkyl 3-aminoazetidine-2-carboxylic esters, a new class of conformationally restricted beta-amino esters, was developed. Reduction of anti-beta,gamma-aziridino-alpha-(N-diphenylmethylidene)amino esters and subsequent regioselective intramolecular ring opening of the beta,gamma-aziridine ring via nucleophilic attack of the alpha-amino function afforded the trans-azetidines.

4-Substituted trinems as broad spectrum beta-lactamase inhibitors: structure-based design, synthesis, and biological activity

A wide variety of pathogens have acquired antimicrobial resistance as an inevitable evolutionary response to the extensive use of antibacterial agents. In particular, one of the most widely used antibiotic structural classes is the beta-lactams, in which the most common and the most efficient mechanism of bacterial resistance is the synthesis of beta-lactamases. Class C beta-lactamase enzymes are primarily cephalosporinases, mostly chromosomally encoded, and are inducible by exposure to some beta-lactam agents and resistant to inhibition by marketed beta-lactamase inhibitors. In an ongoing effort to alleviate this problem a series of novel 4-substituted trinems was designed and synthesized. Significant in vitro inhibitory activity was measured against the bacterial beta-lactamases of class C and additionally against class A. The lead compound LK-157 was shown to be a potent mechanism-based inactivator. Acylation of the active site Ser 64 of the class C enzyme beta-lactamase was observed in the solved crystal structures of two inhibitors complexes to AmpC enzyme from E. cloacae. Structure-activity relationships in the series reveal the importance of the trinem scaffold for inhibitory activity and the interesting potential of the series for further development.

Synthesis of 3-[4′-(p-chlorophenyl)-thiazol-2′-yl]-2-[(substituted azetidinone/thiazolidinone)-aminomethyl]-6-bromoquinazolin-4-ones as anti-inflammatory agent

N-Chloroacetyl-5-bromoanthranilic acid (1), 3-[4'-(p-chlorophenyl)-thiazol-2'-yl]-2-chloromethyl-6-bromoquinazolin-4-one (2), 3-[4'-(p-chlorophenyl)-thiazol-2'-yl]-2-hydrazinomethyl-6-bromoquinazolin-4-one (3), 3-[4'-(p-chlorophenyl)-thiazol-2'-yl]-2-substitutedbenzylidene aminomethyl-6-bromoquinazolin-4-ones (4-11), 2-[(4'-oxo-3'-chloro-2'-phenylazetidin-1'-yl)aminomethyl]-3-[4''-(p-chlorophenyl)thiazol-2''-yl]-6-bromoquinazolin-4-ones (12-19) and 2-(4'-oxo-2'-phenyl-thiazolidin-3'-yl-aminomethyl)- 3-[4''-(p-chlorophenyl)-thiazol-2''-yl]-6-bromoquinazolin-4-ones (20-27) have been synthesized. All the compounds have been screened for their anti-inflammatory and analgesic activities at the dose of 50mg/kg po. Compound 21 showed maximum anti-inflammatory (38.35%) and analgesic (37.36%) activities. Compound 21 was also tested for ulcerogenic activity and the UD(50) value was found to be 195.6mg/kg po. The structure of all compounds has been evaluated by elemental analysis (C, H, N) and spectral analysis (IR, (1)H NMR and mass spectrometry).

Copper-Catalyzed Highly Efficient Multicomponent Reactions: Synthesis of 2-(Sulfonylimino)-4-(alkylimino)azetidine Derivatives

[reaction: see text] Under very mild conditions, functionalized 2-(sulfonylimino)-4-(alkylimino)azetidine derivatives were prepared in good to excellent yields via a copper-catalyzed multicomponent reaction of readily available terminal alkynes, sulfonyl azides, and carbodiimides without the assistance of a base. The mechanism may be through a [2 + 2] cycloaddition.

Quantification of alpha4beta2* nicotinic receptors in the rat brain with microPET and 2-[18F]F-A-85380

The radioligand 2-[(18)F]F-A-85380 has been used for PET studies of the alpha4beta2* subtype of nicotinic acetylcholine receptors (nAChRs) in the living brain of humans and nonhuman primates. In order to extend the capacity of microPET to quantify neuroreceptors in rat brain, we carried out studies of 2-[(18)F]F-A-85380 to measure the apparent binding potential BP* in individual rats, which were studied repeatedly over several months. Using a bolus-plus-infusion paradigm, 2-[(18)F]F-A-85380 (specific activity 20-1300 GBq/micromol) was administered intravenously over 8 to 9 h with K(bol) values of 350 to 440 min and a mean infusion rate of 0.03+/-0.01 nmol/kg/h. Studies included a 2-h nicotine infusion initiated 2 h before the end of scanning to displace specifically bound radioactivity. Steady state binding in brain was obtained within 5 h as defined by the occurrence of constant radioactivity concentrations in brain regions and constant, free arterial plasma levels of nonmetabolized radioligand. BP* averages (+/-SEM) for thalamus, forebrain, and cerebellum were 5.9+/-0.7, 2.6+/-0.4, and 1.0+/-0.1, respectively, which are consistent with the alpha4beta2* nAChR distribution in rat brain measured in vitro. Studies of receptor occupancy determined the ED(50) to be 0.29 nmol/kg/h. The demonstration that alpha4beta2* nAChRs are quantifiable in the rat brain using PET measurements, coupled with the ability to conduct longitudinal studies over several months in the same rats, suggests potential applications to studies of chronic nicotine use, its treatment, and abnormal functioning of alpha4beta2* receptors in a rat model.

N/C-4 substituted azetidin-2-ones: Synthesis and preliminary evaluation as new class of antimicrobial agents

A series of 3-chloro-4-(3-methoxy-4-acetyloxyphenyl)-1-[3-oxo-3-(phenylamino)propanamido] azetidin-2-ones 3a-g and 3-chloro-4-[2-hydroxy-5-(nitro substituted phenylazo)phenyl]-1-phenylazetidin-2-ones 6a-h were synthesized using appropriate synthetic route. Structures of all the synthesized compounds were established on the basis of elemental analysis and spectroscopic data. The antimicrobial activity of the synthesized compounds was screened against several microbes. Several of these molecules showed potent antimicrobial activity against Bacillus anthracis, Staphylococcus aureus and Candida albicans and significant structure-activity relationship (SAR) trends.

A One-Pot Preparation of 1,3-Disubstituted Azetidines

A straightforward synthesis of 1,3-disubstituted azetidines has been accomplished via the alkylation of a primary amine with the bis-triflate of a 2-substituted-1,3-propanediol species. This transformation is carried out in one reaction vessel, and elimination of the alkylating reagent is generally not a major byproduct. The scope of this methodology has been investigated using a variety 2-substituted-1,3-propanediols and amine nucleophiles.

Synthesis of 3-Fluoroazetidines

N-(Alkylidene or 1-arylmethylidene)-2-propenylamines were regiospecifically functionalized to novel N-(alkylidene or 1-arylmethylidene)-3-bromo-2-fluoropropylamines, which were proven to be excellent precursors for 3-fluoroazetidines.

Synthesis of New Thiazolylthiazolidinylbenzothiazoles and Thiazolylazetidinylbenzothiazoles as Potential Insecticidal, Antifungal, and Antibacterial Agents

A series of 2-{[2'-(3''-chloro-2''-oxo-4''-substitutedaryl-1''-azetidinyl)-1',3'-thiazol-4'-yl] thio}benzothiazoles (4a-4e) and 2-{[(2'-(2''-substitutedaryl-4''-thiazolidinon-3''-yl)-1',3'-thiazol-4'-yl]thio}benzothiazoles (5a-5e) have been synthesized from 2-[(2'-substitutedarylidenylimino-1',3'-thiazol-4'-yl)thio]benzothiazoles (3a-3e). The structure of these compounds has been elucidated by elemental (C, H, N) and spectral (IR, (1)H-NMR, Mass) analysis. Furthermore, compounds 3a-3e, 4a-4e, and 5a-5e were screened for insecticidal activity against Periplaneta americana and antifungal, antibacterial activities in vitro against different strains of fungi and bacteria. Out of the fifteen compounds tested, compound 5b, 2-{[2'-(2''-p-hydroxy-m-methoxyphenyl)-4''-thiazolidinon-3''-yl)-1',3'-thiazol-4'-yl]thio}benzothiazole, was found to possess most prominent insecticidal activity.

A Novel Series of Potent and Selective PDE5 Inhibitors with Potential for High and Dose-Independent Oral Bioavailability

Sildenafil (5-[2-ethoxy-5-(4-methyl-1-piperazinylsulfonyl)phenyl]-1-methyl-3-n-propyl-1,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one), a potent and selective phosphodiesterase type 5 (PDE5) inhibitor, provided the first oral treatment for male erectile dysfunction. The objective of the work reported in this paper was to combine high levels of PDE5 potency and selectivity with high and dose-independent oral bioavailability, to minimize the impact on the C(max) of any interactions with coadministered drugs in the clinic. This goal was achieved through identification of a lower clearance series with a high absorption profile, by replacing the 5'-piperazine sulfonamide in the sildenafil template with a 5'-methyl ketone. This novel series provided compounds with low metabolism in human hepatocytes, excellent caco-2 flux, and the potential for good aqueous solubility. The in vivo oral and iv pharmacokinetic profiles of example compounds confirmed the high oral bioavailability predicted from these in vitro screens. 5-(5-Acetyl-2-butoxy-3-pyridinyl)-3-ethyl-2-(1-ethyl-3-azetidinyl)-2,6-dihydro-7H-pyrazolo[4,3-d]pyrimidin-7-one (2) was selected for progression into the clinic.

N,N‘-Carbonyldiimidazole-Mediated Cyclization of Amino Alcohols to Substituted Azetidines and Other N-Heterocycles

Amino alcohols are important synthons for N-heterocycles. We have developed an efficient method to activate hydroxyl groups, which avoids the use of toxic reagents and tolerates a wide variety of functional groups. Our strategy has been applied to the synthesis of functionalized p-methoxyphenyl-protected azetidines, pyrrolidines, and piperidines. The required amino alcohols were synthesized according to an optimized proline-catalyzed Mannich protocol. An azetidine analogue of ezetimibe was synthesized to demonstrate the potential for the synthesis of drug-like molecules.

Synthesis and analgesic activity of secondary amine analogues of pyridylmethylamine and positional isomeric analogues of ABT-594

A series of highly sterically hindered secondary amine analogues of pyridylmethylamine (7a-f, 8a-c) and positional isomeric analogues of ABT-594 (9a-c) were synthesized and evaluated for their in vivo analgesic activity. The compounds 7a and 7d show potent analgesic activity and lower toxicity. Some interesting structure-activity relationships have been revealed.

Electroreductive Intramolecular Coupling of Aromatic Imino Esters: Is Four-Membered Cyclization Much More Favorable than Six-Membered Cyclization?

[reaction: see text] The electroreduction of an aromatic imino ester prepared from (S)-glutamic acid in the presence of chlorotrimethylsilane and triethylamine afforded a four-membered cyclized product, a mixed ketal of cis-2,4-disubstituted azetidine-3-one, stereospecifically. Calculations for the transition states by the DFT method support the predominant formation of the azetidine. The electroreduction of an aromatic imino ester prepared from (S)-aspartic acid gave almost equal amounts of a diastereomerically pure mixed ketal of cis-2,4-disubstituted azetidine-3-one and a diastereomeric mixture of 2,5-disubstituted pyrollidine-3-one.

The Polymer-Supported and Combinatorial Synthesis of β-Lactam Compounds: An Update

Solid-phase organic synthesis (SPOS) has become an effective synthetic tool for the preparation of combinatorial libraries of non-oligomeric small molecules. Owing to their high efficacy and extremely safe toxicological profile, beta-lactam antibiotics are the first choice for bacterial infectious diseases. Moreover, beta-lactam compounds have also showed other biological activities that include inhibition of prostate specific antigen, thrombin, human cytomegalovirus protein, human leukocyte elastase and cholesterol absorption. Thus, the application of combinatorial and related methodologies to the chemistry of the beta-lactam ring has been recognized as a very attractive challenge by different research groups around the world. This review covers the solid-phase and combinatorial chemistry related to mono-and multicyclic beta-lactam compounds that has been reported in the literature from 1999 to 2004.

A Practical and Facile Synthesis of Azetidine Derivatives for Oral Carbapenem, L-084

An orally active carbapenem L-084, which exhibits high bioavailability in humans, has a 1-(1,3-thiazolin-2-yl)azetidin-3-ylthio moiety at the C-2 position of the 1beta-methylcarbapenem skeleton. We established a practical and cost-effective synthesis of 3-mercapto-1-(1,3-thiazolin-2-yl)azetidine (1) for further scale-up production of L-084. This synthesis method entails an industry-oriented reaction of azetidine ring-closure to yield N-benzyl-3-hydroxyazetidine (16), which is eventually converted to 1 via key intermediates, Bunte salts 19 and 20.

Synthesis and in vitro evaluation of inhibitors of intestinal cholesterol absorption

We have utilized our recently developed in vitro assay to address two key questions in the design of small-molecule cholesterol absorption inhibitors using ezetimibe, the only drug yet approved for the inhibition of cholesterol absorption in the small intestine, as a starting point: (1) the role of glycosylation and (2) the importance of the beta-lactam scaffold of ezetimibe for inhibitory activity. A wide range of nonhydrolyzable phenolic glycosides of ezetimibe were synthesized and demonstrated to be active inhibitors of cholesterol absorption using the brush border membrane vesicle assay. The analogous azetidines provided access to a variety of inhibitors in vitro, suggesting that the beta-lactam of ezetimibe merely serves as a ring scaffold to appropriately position the required substituents. Our findings highlight several promising strategies for the design of alternative small-molecule cholesterol absorption inhibitors that could ultimately be useful in preventing cardiovascular disease by lowering blood cholesterol levels.

A simple and fast method for the preparation of n.c.a. 2-[18F]F-A85380 for human use

2-[18F]F-A85380 is the first subtype selective PET-radiotracer to visualize the distribution of alpha4beta2 nicotinic acetylcholine receptors in human brain in vivo. We investigated a fast and safe automated production of 2-[18F]F-A85380 by purification of the BOC-protected intermediate product with a combination of solid phase extraction cartridges. After deprotection, adjustment of the pH and sterile filtration n.c.a. 2-[18F]F-A85380 was applicable for the use in human studies with a high specific activity and an overall radiochemical yield of 55% in 35 minutes.

Synthesis of 2-azetidinones from 2-diazo-1, 2-diarylethanones and N-(2-thienylidene)imines as possible antimicrobial agents

An equimolar reaction of 2-diazo-1, 2-diarylethanones with N-(2-thienylidene)imines affords 1-substituted-3, 3-diaryl-4-(2-thienyl)-2-azetidinones in excellent yields. The products have been characterized on the basis of satisfactory analytical and spectral (IR, 1H and 13C NMR, MS) data. The mechanism of formation of the products is shown. The antimicrobial activity of the compounds against some Gram(+) and Gram(-) bacteria, and fungi is reported.

Design, Synthesis, and Enzymatic Evaluation of N-Acyloxyalkyl- and N1-Oxazolidin-2,4-dion-5-yl-Substituted β-lactams as Novel Inhibitors of Human Leukocyte Elastase

Human leukocyte elastase (HLE) is a serine protease that very efficiently degrades various tissue matrix proteins such as elastin. The imbalance between HLE and its endogenous inhibitors leads to excessive elastin proteolysis and is considered to be responsible for the onset of chronic obstructive pulmonary disease (COPD). A novel series of C-3-, C-4-, and N-1-substituted azetidin-2-ones were prepared as potential mechanism-based inhibitors of HLE to restore the protease/antiprotease imbalance. N-Acyloxyalkylazetidin-2-ones, 4, and their carbamate counterparts, 5, are weak HLE inhibitors, being 5 times less active than their bicyclic oxazolidin-2,4-dione-substituted analogues, 6, containing an electron-withdrawing substituent at C-4. Compounds 6 containing a C-4 substituent exist as two diastereomeric pairs of enantiomers, each pair presenting similar inhibitory activity against HLE. Comparative docking experiments with the C-4-substituted oxazolidin-2,4-dione inhibitors 6 suggest that only the 4R,5'S and 4S,5'S diastereomers consistently interact with the beta-lactam carbonyl carbon atom accessible to the serine hydroxyl oxygen.

Approaches to Syn-7-Substituted 2-Azanorbornanes as Potential Nicotinic Agonists; Synthesis of syn- and anti-Isoepibatidine

[reaction: see text] Coupling of N-Boc-7-bromo-2-azabicyclo[2.2.1]heptane with aryl and pyridyl boronic acids incorporates aryl and heterocyclic substituents at the 7-position and leads to a preference for syn over anti stereoisomers. Incorporation of a chloropyridyl group followed by N-deprotection gives syn-isoepibatidine. Facial selectivity in attack on 7-keto-2-azanorbornanes depends heavily on the N-protecting group leading to the first syn-7-hydroxy-2-azabicyclo[2.2.1]heptane derivative.

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.