Hypocholesterolemic activity of some novel azetidin-2-ones in diet and diabetes induced hypercholesterolemia in rats

Some novel substituted azetidin-2-ones (5-8) were synthesized via [2 + 2] cycloaddition reactions of imines and ketenes and evaluated for their ability to prevent diet and diabetes induced hypercholesterolemia. The test compounds 5a and 7a significantly (p < 0.01) inhibited the rise in serum total cholesterol induced by peanut oil (5.5%), cholesterol (1.5%) and cholic acid (0.5%) diet in both acute and chronic models in a dose dependent manner. Compound 5a also raised the high density lipoprotein-cholesterol levels in chronic diet models by peanut oil (5.5%), cholesterol (1.5%) and cholic acid (0.5%). In a diabetes induced model of hypercholesterolemia, the test compounds were evaluated for preventing diabetes-induced hypercholesterolemia (protocol 1) as well as for lowering post diabetic hypercholesterolemia (protocol 2). Test compounds 5a-g and 7a-d significantly (p < 0.05) reduced serum total cholesterol with a greater reduction in protocol 1 as compared with protocol 2. Based on SAR studies, the substituents that favor hypocholesterolemic activity around the azetidin-2-one nucleus are discussed and a possible mechanism of action is proposed on the basis of their differential effects in two protocols of diabetes-induced hypercholesterolemia.

3,4-Disubstituted azetidinones as selective inhibitors of the cysteine protease cathepsin K. Exploring P3 elements for potency and selectivity

The synthesis of a series of highly potent and selective inhibitors of cathepsin K based on the 3,4-disubstituted azetidin-2-one warhead is reported. A high degree of potency and selectivity was achieved by introducing a basic nitrogen into the distal part of the P3 element of the molecule. Data from kinetic and mass spectrometry experiments are consistent with the interpretation that compounds of this series transiently acylate the sulfhydrile of cathepsin K.

3-(2,5-Dihydro-1H-pyrrol-2-ylmethoxy)pyridines: synthesis and analgesic activity

We disclose an efficient procedure for the preparation of ethers of 2-substituted 2-hydroxymethylpyrroline and of 2-aminomethyl-3-pyrrolines, involving, as a key step, formation and nucleophilic ring opening of a cyclic sulfamidate. Several new analogs of epibatidine (1) and tebanicline (ABT-594, 2) were prepared and tested for analgesic activity in the mouse formalin model.

Carbohydrate Sulfonyl Chlorides for Simple, Convenient Access to Glycoconjugates

[reaction: see text] The use of carbohydrate sulfonyl chlorides is introduced as a new, facile glycoconjugation method which could find broad applications. We demonstrate the approach by synthesizing a number of glycosylated cholesterol absorption inhibitors which display high inhibitory efficacies in our recently established in vitro assay. Furthermore, we highlight an advantage of the electron-withdrawing nature of the sulfonyl linkage which allowed the synthesis of otherwise unstable azetidine conjugates.

A novel azetidinyl γ-lactam based peptide with a preference for β-turn conformation

Novel azetidinyl gamma-lactam based peptides have been synthesized with only compound showing a preference for the beta-turn conformation.

Azetidinic amino acids: stereocontrolled synthesis and pharmacological characterization as ligands for glutamate receptors and transporters

A set of ten azetidinic amino acids, that can be envisioned as C-4 alkyl substituted analogues of trans-2-carboxyazetidine-3-acetic acid (t-CAA) and/or conformationally constrained analogues of (R)- or (S)-glutamic acid (Glu) have been synthesized in a diastereo- and enantiomerically pure form from beta-amino alcohols through a straightforward five step sequence. The key step of this synthesis is an original anionic 4-exo-tet ring closure that forms the azetidine ring upon an intramolecular Michael addition. This reaction was proven to be reversible and to lead to a thermodynamic distribution of two diastereoisomers that were easily separated and converted in two steps into azetidinic amino acids. Azetidines 35-44 were characterized in binding studies on native ionotropic Glu receptors and in functional assays at cloned metabotropic receptors mGluR1, 2 and 4, representing group I, II and III mGlu receptors, respectively. Furthermore, azetidine analogues 35, 36, and 40 were also characterized as potential ligands at the glutamate transporter subtypes EAAT1-3 in the FLIPR Membrane Potential (FMP) assay. The (2R)-azetidines 35, 37, 39, 41 and 43 were inactive in iGlu, mGlu and EAAT assays, whereas a marked change in the pharmacological profile at the iGlu receptors was observed when a methyl group was introduced in the C-4 position, compound 36 versus t-CAA. At EAAT1-3, compound 35 was inactive, whereas azetidines 36 and 40 were both identified as inhibitors and showed selectivity for the EAAT2 subtype.

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.

2-Aryl-N-tosylazetidines as Formal 1,4-Dipoles for [4 + 2] Cycloaddition Reactions with Nitriles: An Easy Access to the Tetrahydropyrimidine Derivatives

[reaction: see text] A new synthetic route to 2-aryl-N-tosyl azetidines has been developed starting from N-tosylarylaldimines in two steps in an overall yield of 63-70%. A formal [4 + 2] cycloaddition of these 2-aryl-N-tosylazetidines with nitriles in the presence of BF3.OEt2 has been described for the synthesis of substituted tetrahydropyrimidines. It is proposed that the reaction proceeds in Ritter fashion.

1,3,3-Trinitroazetidine (TNAZ), a melt-cast explosive: synthesis, characterization and thermal behaviour

1,3,3-Trinitroazetidine (TNAZ) has been prepared at a laboratory scale in HEMRL. The structure of the compound has been confirmed by IR, NMR, mass, elemental analysis and by X-ray crystallography. HPLC technique has been employed to confirm the purity of TNAZ (>99%). The compound is further characterized by thermal techniques and is found to undergo limited decomposition at its melting point. Small scale sensitivity tests have also been carried out and the results show that TNAZ is significantly more sensitive to mechanical stimuli than TNT.

Azetidin-2-ones, Synthon for Biologically Important Compounds †

Azetidin-2-one, a four-membered cyclic lactam (beta-lactam) skeleton has been recognised as a useful building block for the synthesis of a large number of organic molecules by exploiting the strain energy associated with it, in addition to its use in the synthesis of a variety of beta-lactam antibiotics. Efforts have been made in exploring such new aspects of beta-lactam chemistry using enantiomerically pure beta-lactams as versatile intermediates for the synthesis of aromatic beta-amino acids and their derivatives, peptides, polyamines, polyamino alcohols, amino sugars and polyamino ethers. The development of methodologies based on beta-lactam nucleus is now referred as 'the beta-lactam synthon methods'. The selective bond cleavage of the strained ring coupled with further interesting transformation render this fascinating molecule as a powerful building block. This provides an access to diverse structural type of synthetic target molecules lacking beta-lactam ring structure. This review provides an account of synthesis of organic compounds having biological significance at the same time lacking beta-lactam ring, by using beta-lactam as synthon.

5-substituted derivatives of 6-halogeno-3-((2-(S)-azetidinyl)methoxy)pyridine and 6-halogeno-3-((2-(S)-pyrrolidinyl)methoxy)pyridine with low picomolar affinity for alpha4beta2 nicotinic acetylcholine receptor and wide range of lipophilicity: potential probes for imaging with positron emission tomography

Potential positron emission tomography (PET) ligands with low picomolar affinity at the nicotinic acetylcholine receptor (nAChR) and with lipophilicity (log D) ranging from -1.6 to +1.5 have been synthesized. Most members of the series, which are derivatives of 5-substituted-6-halogeno-A-85380, exhibited a higher binding affinity at alpha4beta2-nAChRs than epibatidine. An analysis, by molecular modeling, revealed an important role of the orientation of the additional heterocyclic ring on the binding affinity of the ligands with nAChRs. The existing nicotinic pharmacophore models do not accommodate this finding. Two compounds of the series, 6-[(18)F]fluoro-5-(pyridin-3-yl)-A-85380 ([(18)F]31) and 6-chloro-3-((2-(S)-azetidinyl)methoxy)-5-(2-[(18)F]fluoropyridin-5-yl)pyridine) ([(18)F]35), were radiolabeled with (18)F. Comparison of PET data for [(18)F]31 and 2-[(18)F]FA shows the influence of lipophilicity on the binding potential. Our recent PET studies with [(18)F]35 demonstrated that its binding potential values in Rhesus monkey brain were ca. 2.5 times those of 2-[(18)F]FA. Therefore, [(18)F]35 and several other members of the series, when radiolabeled, will be suitable for quantitative imaging of extrathalamic nAChRs.

Evaluation of 5-(11)C-methyl-A-85380 as an imaging agent for PET investigations of brain nicotinic acetylcholine receptors

Central nicotinic acetylcholine receptors (nAChRs) represent major neurotransmitter receptors responsible for various brain functions, and changes in the density of nAChRs have recently been reported in several neurodegenerative diseases. Visualization of nAChRs in human brain has thus been of great interest, and the development of radiopharmaceuticals for the imaging and quantitative assessment of central nAChRs has been desired. In this study, we synthesized 5-(11)C-methyl-3-(2-(S)-azetidinylmethoxy)pyridine (5MA), a derivative of 3-(2-(S)-azetidinylmethoxy)pyridine (A-85380) (11)C-methylated at position 5 of the pyridyl fragment, and evaluated its potential for investigating central nAChRs by PET.

METHODS

(11)C-5MA was synthesized by the incorporation of (11)C-methyl iodide into 5-butylstannyl A-85380, using a Pd-catalyzed coupling reaction. The affinity of 5MA for central nAChRs was measured by displacement of (-)-(3)H-cytisine from binding sites in rat cortical membranes. The biodistribution of (11)C-5MA was determined with mice. PET studies were performed on rhesus monkeys with a high-resolution PET scanner for animals.

RESULTS

The overall synthesis time was 60 min from the end of radionuclide production, and the radiochemical yield, after purification by high-performance liquid chromatography, was 30%. The radiochemical purity of the product was >99%, with a specific radioactivity of >36 GBq/ micro mol. In vitro receptor-binding assays demonstrated that 5MA has a high, selective binding affinity for nAChRs, being approximately 1.5-fold higher than that of A-85380, 3.5-fold higher than that of (-)-cytisine, and 10-fold higher than that of (-)-nicotine. The distribution studies in mice showed that the brain uptake of (11)C-5MA was profound. Regional cerebral distribution studies in mice demonstrated that the accumulation of (11)C-5MA was consistent with the density of nAChRs, with the highest uptake observed in the thalamus, a moderate uptake in the cortex and striatum, and the lowest uptake in the cerebellum. Furthermore, preinjection of nAChR-binding ligands, (-)-nicotine and (-)-cytisine, reduced the uptake of (11)C-5MA in brain regions of high uptake in the untreated experiment. PET imaging studies with (11)C-5MA in rhesus monkeys demonstrated clear images consistent with the distribution of nAChRs in the brain.

CONCLUSION

These results suggest that (11)C-5MA is a potential PET radiopharmaceutical for nuclear medical studies of nAChRs in the brain.

Solid-phase synthesis and SAR of 4-carboxy-2-azetidinone mechanism-based tryptase inhibitors

A series of nonguanidine N1-activated C4-carboxy azetidinone tryptase inhibitors was prepared by solid-phase methodology to quickly assess the SAR associated with distal functionality on the N1-activating group. From these studies, potent inhibitors with improved specificity were discovered.

Synthesis of potent and highly selective nonguanidine azetidinone inhibitors of human tryptase

Azetidinones such as BMS-363131 (2) and BMS-363130 (3), which contain a guanidine group in the C-3 side chain were previously shown to be very potent inhibitors of human tryptase with high selectivity versus other serine proteases, including trypsin. In this letter, we describe the discovery of a number of potent azetidinone tryptase inhibitors in which the guanidine moiety at the ring C-3 position is replaced with primary or secondary amine or aminopyridine functionality. In particular, BMS-354326 (4) is a highly potent tryptase inhibitor (IC(50)=1.8 nM), which has excellent selectivity against trypsin and most other related serine proteases.

Straightforward Asymmetric Entry to Highly Functionalized 3-Substituted 3-Hydroxy-β-lactams via Baylis−Hillman or Bromoallylation Reactions

The reaction of various activated vinyl systems, including 2-cyclopenten-1-one, with enantiopure azetidine-2,3-diones 1 was promoted by DABCO to afford the corresponding optically pure Baylis-Hillman adducts 2 without detectable epimerization. However, the reaction of alpha-keto lactams 1 with but-3-yn-2-one was not as successful, giving the corresponding beta-halo Baylis-Hillman adduct in low yield. Metal-mediated bromoallylation reaction between 2,3-dibromopropene and azetidine-2,3-diones 1 was investigated in aqueous media. Surprisingly, indium was unable to promote the bromoallylation reaction of alpha-keto lactams 1, but the Sn-Hf(4)Cl-promoted bromoallylation of ketones 1 proceeded efficiently to achieve bromohomoallyl alcohols 5 as single diastereomers. On this basis, simple and fast protocols for the asymmetric synthesis of the potentially bioactive 3-substituted 3-hydroxy-beta-lactam moiety were developed.

Synthesis and evaluation of N1/C4-substituted β-lactams as PPE and HLE inhibitors

4-(Alkylamino)carbonyl-1-(alkoxy)carbonyl-2-azetidinones (9-11) have been prepared in five steps from 4-(benzyloxy)carbonyl-1-(t-butyldimethyl)silyl-2-azetidinone (1). The beta-lactam reactivity of 9 has been established by 1H NMR experiment. Compound 11 was a good reversible inhibitor of PPE and HLE. Based on theoretical design, series of 2-azetidinones (12-17) and 4-(alkoxy)carbonyl-2-azetidinones (18-21) bearing various carbonyl (ester, thiolester, amide) and thiocarbonyl (thioamide) functionalities at position N1 were similarly prepared. In the absence of C4-substituent, the compounds were inactive against elastases. On the other hand, 4-(benzyloxy)carbonyl-1-(ethylthioxy)carbonyl-2-azetidinone (19) and 4-(benzyloxy)carbonyl-1-(benzylamino)thiocarbonyl-2-azetidinone (21) were both good reversible inhibitors, but acting most probably via different mechanisms (enzymic processing of the exocyclic ester function or beta-lactam ring opening).

Synthesis of antitumor 6-alkylidenepenicillanate sulfones and related 3-alkylidene-2-azetidinones

6-alkylidenepenicillanate sulfoxides and sulfones were synthesized on the base of 6-oxopenicillanate esters. The targeted splitting of their thiazolidine ring led to the formation of 3-alkylidene substituted 4-heteryldithio and 4-methylsulfonyl azetidin-2-ones. Some of mono and bicyclic beta-lactams revealed potent cytotoxic properties towards monolayer tumor cells in <10-microM concentrations.

4-Alkylidene-azetidin-2-ones: novel inhibitors of leukocyte elastase and gelatinase

In addition to their antibiotic potency, beta-lactams have recently been investigated as inhibitors of serine proteinase such as leukocyte elastase (LE), released by inflammatory cells. We describe the synthesis of a series of 4-alkylidene-beta-lactams, and investigate how substitutions on C-3, C-4, and N-1 of the beta-lactam ring affect the activity of human LE and gelatinases MMP-2 and MMP-9. LE activity was measured using a chromogenic substrate, while gelatin-zymography assay was used to evaluate gelatinase activity. We demonstrate that C-4 unsaturation on the beta-lactam ring determines the degree of biological activity, with a selectivity over LE by 3-[1-(tert-butyldimethylsilyloxy)-ethyl] derivatives (lowest IC(50) was 4 microM), and over gelatinase MMP-2 by C-3-unsubstituted 4-[1-ethoxycarbonyl]-ethylidene-beta-lactams (lowest IC(50) was 60 microM). (3S)-3-[(1R)-1-hydroxyethyl]-4-(1-ethoxycarbonyl)-ethylidene-azetidin-2-one inhibits gelatinase MMP-9. The compounds tested showed no cytotoxicity against NIH-3T3 murine fibroblasts. This is the first example of beta-lactams inhibiting metallo-proteinases instrumental in cancer invasion and angiogenesis. These molecules are good candidates for prototype drugs showing selective antibiotic, anti-inflammatory, and anti-invasion properties.

Synthesis and anti-inflammatory activity of alkyl/arylidene-2-aminobenzothiazoles and 1-benzothiazol-2-yl-3-chloro-4-substituted-azetidin-2-ones

Ten new derivatives of 1-benzothiazol-2-yl-3-chloro-4-substituted-azetidin-2-ones (3a-j) were synthesized using various Schiff bases (alkyl/arylidene-2-aminobenzothiazoles; 2a-j), which in turn were prepared starting from 2-aminobenzothiazole (1). All the synthesised compounds were characterised by elemental analyses and spectral (IR, 1H-NMR, 13C-NMR and EI-MS) data. The title compounds 2a-j and 3a-j were screened in vivo using carrageenan-induced rat paw edema model. All the test compounds showed anti-inflammatory activity when tested in vivo. In general, compounds 3a-j were found to be more potent compared to compounds 2a-j. Among the compounds tested, compound 2g in the alkyl/arylidene-2-aminobenzothiazoles series and compound 3 g in the 1-benzothiazol-2-yl-3-chloro-4-substituted-azetidin-2-ones series were found to be the most potent. All the test compounds were also evaluated to check the gastric ulcer incidence. In gastric ulceration studies, all the test compounds were generally found to be safe at the 100 mg/kg dose level. Furthermore the most potent compounds 2 g and 3 g from each series were screened in vitro for inhibition of both COX-2 and COX-1 catalysed prostaglandin biosynthesis (radiochemical assay). Like most of the commercially available non-steroidal anti-inflammatory drugs (NSAIDs), in the in vitro study, compounds 2 g and 3 g showed anti-inflammatory activity by blocking the metabolism of arachidonic acid to prostaglandin via the cyclooxygenase pathways. In general, in the vitro assay, test compounds 2 g and 3 g were found to be more active after 15 min pre-incubation with the enzyme. Compound 3 g was found to be more COX-2 selective, while compound 2 g was found to be equally COX-2 and COX-1 selective.

Synthesis of Cryptophycins via an N-Acyl-β-lactam Macrolactonization

An efficient and concise approach to the synthesis of the macrolide core of the cryptophycins has been developed. A novel macrolactonization utilizing a reactive acyl-beta-lactam intermediate incorporates the beta-amino acid moiety within the 16-membered macrolide core. This modular approach, involving a cyanide-initiated acyl-beta-lactam ring opening followed by cyclization, was successfully applied to the total synthesis of cryptophycin-24. The strategy was also used in an efficient synthesis of the 6,6-dimethyl-substituted dechlorocryptophycin-52. In this case, the cyanide-initiated ring opening of the bis-substituted 2-azetidinone followed by macrolactonization was achieved through a catalytic process.

Cyclic amine sulfonamides as linkers in the design and synthesis of novel human beta(3) adrenergic receptor agonists

Piperidine, pyrrolidine, and azetidine sulfonamides were examined as linkers in designing novel human beta(3) adrenergic receptor (beta(3)-AR) agonists. The azetidine derivative 37, and piperidine derivatives 7, 8, and 13 were found to be potent beta(3)-AR agonists and have good selectivity against beta(1)- and beta(2)-AR.

3,4-disubstituted azetidinones as selective inhibitors of the cysteine protease cathepsin K. Exploring P2 elements for selectivity

A novel series of 3,4-disubstituted azetidinones based inhibitors of the cysteine protease cathepsin K (Cat K) has been identified. Although not optimized, some of these compounds show at least 100-fold selectivity against other cathepsins. The use of cyclic moieties as P2 elements has proven to be crucial to achieve a high degree of selectivity.

A novel antibacterial 8-chloroquinolone with a distorted orientation of the N1-(5-amino-2,4-difluorophenyl) group

Fluoroquinolones represent a major class of antibacterial agents with great therapeutic potential. In this study, we designed m-aminophenyl groups as novel N-1 substituents of naphthyridones and quinolones. Among newly synthesized compounds, 7-(3-aminoazetidin-1-yl)-1-(5-amino-2,4-difluorophenyl)-8-chloro-6-fluoro-4-oxo-1,4-dihydroquinoline-3-carboxylic acid (4) has extremely potent antibacterial activities against Gram (+) as well as Gram (-) bacteria. This compound is significantly more potent than trovafloxacin against clinical isolates: 30 times against Streptococcus pneumoniae and 128 times against methicillin resistant Staphylococcus aureus. The structure-activity relationship (SAR) study revealed that a limited combination of 1-(5-amino-2,4-difluorophenyl) group, 7-(azetidin-1-yl) group, and 8-Cl atom (or Br atom or Me group) gave potent antibacterial activity. An X-ray crystallographic study of a 7-(3-ethylaminoazetidin-1-yl)-8-chloro derivative demonstrated that the N-1 aromatic group was remarkably distorted out of the core quinolone plane by steric repulsion between the C-8 Cl atom and the N-1 substituent. Furthermore, a molecular modeling study of 4 and its analogues demonstrated that a highly distorted orientation was induced by a steric hindrance of the C-8 substituent, such as Cl, Br, or a methyl group. Thus, their highly strained conformation should be a key factor for the potent antibacterial activity.

Synthesis of a biotin-tagged photoaffinity probe of 2-azetidinone cholesterol absorption inhibitors

The design and synthesis of a biotin-tagged photoreactive analogue C-4 of the cholesterol absorption inhibitor Ezetimibe is described. Photoaffinity labeling of intestinal brush border membrane vesicles with C-4 and subsequent streptavidin-biotin chromatography leads to selective extraction of a 145 kDa integral membrane protein as the molecular target for cholesterol absorption inhibitors.

Synthesis and biological evaluation of 4-deacetoxy-1,7-dideoxy azetidine paclitaxel analogues

Three novel 4-deacetoxy-1,7-dideoxy azetidine paclitaxel analogues were synthesized through a convenient route that employed hydroboration-amination and intramolecular S(N)2-type substitution reaction from a natural taxoid taxinine. All analogues have been tested for cytotoxicity against three human tumor cell lines. None of them showed remarkable cytotoxicity compared to paclitaxel against tested tumor cell lines.