3-Acylamino-azetidin-2-one as a novel class of cysteine proteases inhibitors

A new class of inhibitors for cysteine proteases cathepsin B, L, K and S is described. These inhibitors are based on the beta-lactam ring designed to interact with the nucleophilic thiol of the cysteine in the active site of cysteine proteases. Some 3-acylamino-azetidin-2-one derivatives showed very potent inhibition activities for cathepsins L, K and S at the nanomolar or subnanomolar IC(50) values.

Stereospecific synthesis of azetidine-cis-2,3-dicarboxylic acid

Electrocyclic reaction product of 1-(methoxycarbonyl)-1,2-dihydropyridine was stereospecifically converted by RuO(4) oxidation into azetidine-cis-2,3-dicarboxylic acid.

1-Alkoxycarbonyl-3-halogenoazetidin-2-ones as elastase (PPE) inhibitors

A series of 1-alkoxycarbonyl-3-halogenoazetidin-2-ones, designed as potential suicide inhibitors of serine proteases, has been synthesized and evaluated against porcine pancreatic elastase (PPE). All the compounds were transient inhibitors, their activity depending mainly on the nature of the halogen substituent: bromo- and iodo- derivatives are more active (K(i) approximately 2-22 microM) than 3-chloroazetidinones (K(i) approximately 20-150 microM). The lipophilicity of the N-1 substituent appeared to exert a slightly positive effect.

Structure-activity relationships of 1-alkyl-5-(3,4-dichlorophenyl)- 5-[2-[(3-substituted)-1-azetidinyl]ethyl]-2-piperidones. 1. Selective antagonists of the neurokinin-2 receptor

The design, synthesis, and pharmacological evaluation of a novel class of neurokinin-2 (NK2) antagonists 1-alkyl-5-(3,4-dichlorophenyl)-5-[2-[(3-substituted)-1-azetidinyl]ethyl]-2-piperidones (5-44) are described. These compounds are formally derived from 2 by incorporating the metabolically vulnerable N-methylamide function into a more stable six-membered ring lactam 4, resulting in increased stability in human liver microsome (HLM) preparations relative to 2 (T1/2(HLM) of 30 min vs <10 min for 2). This series was further optimized by replacing the 4,4-disubstituted piperidine functionality found in 4 with simple 3-substituted azetidines. This series, exemplified by 1-benzyl-5-(3,4-dichlorophenyl)-5-[2-[3-(4-morpholinyl)-1-azetidinyl]ethyl]-2-piperidone 5, was found to possess excellent functional potency for the NK2 receptor in the Rabbit pulmonary artery (RPA) assay (pA2 = 9.3) and increased in vitro metabolic stability (T1/2(HLM) = 70 min) relative to 4. Metabolic route identification studies revealed that N-benzyl oxidation was a major route in this relatively lipophilic lead (log D = 3.2). Further exploration of the N-lactam substituent SAR targeting reduced lipophilicity to attenuate P-450 metabolism revealed that incorporation of a cyclopropylmethyl group in this region of the molecule gave a balance of good potency and high metabolic stability. For example, the significantly less lipophilic analogue 29 (log D = 2.3) possessed both good functional potency (RPA, pA2 = 8.1) and high in vitro metabolic stability (T1/2(HLM) = 120 min). Optimization in this N-cyclopropylmethyllactam series by modification of the nature of the azetidine 3-substituent as a strategy to further increase potency and moderate log D led to the identification of sulfamide analogue 33, which possessed both excellent metabolic stability in vitro (T1/2(HLM) >120 min) and high potency in both RPA (pA2 = 8.9) and human bladder smooth muscle (pK(b) = 8.9) functional assays. In addition, NK2 antagonist 33 (IC50 = 4 nM) showed excellent selectivity over both the related human neurokinin receptors h-NK1 (IC50 = 7.9 microM) and h-NK3 (IC50 = 1.8 microM) in radioligand binding studies.

Synthesis and SAR of 4-carboxy-2-azetidinone mechanism-based tryptase inhibitors

A series of N1-activated C4-carboxy azetidinones was prepared and tested as inhibitors of human tryptase. The key stereochemical and functional features required for potency, serine protease specificity and aqueous stability were determined. From these studies compound 2, BMS-262084, was identified as a potent and selective tryptase inhibitor which, when dosed intratracheally in ovalbumin-sensitized guinea pigs, reduced allergen-induced bronchoconstriction and inflammatory cell infiltration into the lung.

Synthesis of potent and highly selective inhibitors of human tryptase

The serine protease tryptase has been implicated in allergic and inflammatory diseases and associated with asthma. The synthesis and SAR of a series of N1-activated-4-carboxy azetidinones are described, resulting in identification of BMS-363131 (2) as a potent inhibitor of human tryptase (IC(50)<1.7 nM) with high selectivity (>3000-fold) for tryptase versus related serine proteases including trypsin.

Synthesis and structure-activity relationships of aminoalkylazetidines as ORL1 receptor ligands

A series of aminoalkylazetidines has been discovered as novel ORL1 receptor ligands. Structure-activity relationships have been investigated at the azetidine N and the alkyl side chain sites. Several potent and selective analogues have been identified.

Efficient entry to highly functionalized beta-lactams by regio- and stereoselective 1,3-dipolar cycloaddition reaction of 2-azetidinone-tethered nitrones. Synthetic applications

Racemic as well as optically pure 2-azetidinone-tethered nitrones, both cyclic and acyclic, were smoothly prepared from 4-oxoazetidine-2-carbaldehydes. The regio- and diastereoselectivities of the intermolecular 1,3-dipolar cycloaddition reactions of 2-azetidinone-tethered nitrones with substituted alkenes and alkynes were investigated. 2-Azetidinone-tethered nitrones on reacting with various dipolarophiles yielded isoxazolinyl-, isoxazolidinyl-, or fused polycyclic-beta-lactams, exhibiting good regio- and facial stereoselectivity in the most of the cases. In addition, some interesting transformations of these cycloadducts were performed, yielding aziridinyl beta-lactams or functionalized beta-alkoxycarbonyl gamma-lactams (derivatives of the aza analogue of paraconic acid).

Lysergamides of isomeric 2,4-dimethylazetidines map the binding orientation of the diethylamide moiety in the potent hallucinogenic agent N,N-diethyllysergamide (LSD)

Lysergic acid amides were prepared from (R,R)-(-)-, (S,S)-(+)-, and cis-2,4-dimethyl azetidine. The dimethylazetidine moiety is considered here to be a rigid analogue of diethylamine, and thus, the target compounds are all conformationally constrained analogues of the potent hallucinogenic agent, N,N-diethyllysergamide, LSD-25. Pharmacological evaluation showed that (S,S)-(+)-2,4-dimethylazetidine gave a lysergamide with the highest LSD-like behavioral activity in the rat two lever drug discrimination model that was slightly more potent than LSD itself. This same diastereomer also had the highest affinity and functional potency at the rat serotonin 5-HT(2A) receptor, the presumed target for hallucinogenic agents, and a receptor affinity profile in a panel of screens that was most similar to that of LSD itself. Both cis- and the (R,R)-trans-dimethylazetidines gave lysergamides that were less potent in all relevant assays. The finding that the S,S-dimethylazetidine gave a lysergamide with pharmacology most similar to LSD indicates that the N,N-diethyl groups of LSD optimally bind when they are oriented in a conformation distinct from that observed in the solid state by X-ray crystallography. The incorporation of isomeric dialkylazetidines into other biologically active molecules may be a useful strategy to model the active conformations of dialkylamines and dialkylamides.

A stereoselective synthesis of BMS-262084, an azetidinone-based tryptase inhibitor

A highly stereoselective synthesis of the novel tryptase inhibitor BMS-262084 was developed. Key to this synthesis was the discovery and development of a highly diastereoselective demethoxycarbonylation of diester 12 to form the trans-azetidinone 13. BMS-262084 was prepared in 10 steps from D-ornithine in 30% overall yield.

General approach for the stereocontrolled construction of the beta-lactam ring in amino acid-derived 4-alkyl-4-carboxy-2-azetidinones

The first general approach toward the asymmetric synthesis of 4-alkyl-4-carboxy-2-azetidinones derived from amino acids is described. The stereoselective construction of the beta-lactam ring was achieved through base-mediated intramolecular cyclization of the corresponding N(alpha)-chloroacetyl derivatives bearing (+)- or (-)-10-(N,N-dicyclohexylsulfamoyl)isoborneol as chiral auxiliary (ee up to 82%).

BINOL-catalyzed highly enantioselective terminal alkyne additions to aromatic aldehydes

[reaction: see text] The readily available BINOL ligand in combination with Ti(O(i)Pr)(4) was found to catalyze the highly enantioselective reaction (92-98% ee) of terminal alkynes with aromatic aldehydes that contain a variety of substituents and substitution patterns. After the preparation of the zinc acetylide reagent, the catalytic asymmetric addition to aldehydes proceeded at room temperature with excellent stereocontrol. This simple catalyst system is practical for the asymmetric synthesis of chiral propargylic alcohols.

Evaluation of radioiodinated 5-iodo-3-(2(S)-azetidinylmethoxy)pyridine as a ligand for SPECT investigations of brain nicotinic acetylcholine receptors

5-Iodo-3-(2(S)-azetidinylmethoxy)pyridine (5IA), an A-85380 analog iodinated at the 5-position of the pyridine ring, was evaluated as a radiopharmaceutical for investigating brain nicotinic acethylcholine receptors (nAChRs) by single photon emission computed tomography (SPECT). [123/125I]5IA was synthesized by the iododestannylation reaction under no-carrier-added conditions and purified by high-performance liquid chromatography (HPLC) with high radiochemical yield (50%), high radiochemical purity (> 98%), and high specific radioactivity (> 55 GBq/micromol). The binding affinity of 5IA for brain nAChRs was measured in terms of displacement of [3H]cytisine and [125I]5IA from binding sites in rat cortical membranes. The binding data revealed that the affinity of 5IA was the same as that of A-85380 and more than seven fold higher than that of (-)-nicotine, and that 5IA bound selectively to the alpha4beta2 nAChR subtype. Biodistribution studies in rats indicated that the brain uptake of [125I]51A was rapid and profound. Regional cerebral distribution studies in rats demonstrated that the accumulation of [125I]5IA was consistent with the density of high affinity nAChRs with highest uptake observed in the nAChR-rich thalamus, moderate uptake in the cortex and lowest uptake in the cerebellum. Administration of the nAChR agonists (-)-cytisine and (-)-nicotine reduced the uptake of [125I]5IA in all regions studied with most pronounced reduction in the thalamus, and resulted in similar levels of radioactivity throughout the brain. [125I]5IA binding sites were shown to be saturable with unlabeled 5IA. Behavioral studies in mice demonstrated that 5IA did not show signs of behavioral toxicity. Furthermore, SPECT studies with [123I]5IA in the common marmoset demonstrated appropriate brain uptake and regional localization for a high-affinity nAChR imaging radiopharmaceutical. These results suggested that [123I]5IA is a promising radiopharmaceutical for SPECT studies of central nAChRs in human subjects.

SmI(2)-mediated cyclizations of derivatized beta-lactams for the highly diastereoselective construction of functionalized prolines

A series of C4-keto-functionalized 1-[(benzoyloxy)(ethoxycarbonyl)methyl]-2-azetidinones were prepared and studied for their tendency to undergo a Reformatsky-type cyclization to fused bicyclic or tricyclic beta-lactams with the single-electron reducing agent samarium diiodide. Whereas the azetidinone 21a underwent reductive cyclization, affording the potent antibiotic sanfetrinem's tricyclic [4.5.6] core structure as the major component, all other examples tested resulted in cyclization followed by an N to O acyl migration involving cleavage of the beta-lactam ring as the favored pathway. Highly functionalized proline derivatives were therefore accessed as single diastereomers through the reductive cyclization of benzoates 21b, 22, 23a,b, 24b, and 25-28. Pertinent for the success of these cyclizations was the addition of 1 equiv of tert-butyl alcohol, allowing for the protonation of the basic amide derivative obtained after the acyl migration step. The diastereoselectivities of these reactions deviate from those of similar cyclizations involving the corresponding lithium enolate. This divergence could be rationalized by the coordination of the metal ion of the samarium(III) enolate intermediate to the beta-lactam amide functionality in the cyclization step, which may not be possible for lithium enolates.

Ezetimibe. Schering-Plough

Ezetimibe (Sch-58235) is a cholesterol absorption inhibitor under development by Schering-Plough (SP), in collaboration with Merck, for the potential treatment of hypercholesterolemia. In late December 2001, the companies filed an NDA in the US for this indication. SP is studying ezetimibe as a monotherapy for lowering lipid levels, and also in combination with commonly used statins therapies. The company believes that ezetimibe will have additive effects with the statins, inhibiting the absorption of cholesterol in the intestine, while the statins work by inhibiting the production of cholesterol in the liver. In May 2000, SP and Merck signed an agreementfor the codevelopment of ezetimibe covering its uses as a monotherapy, in combination with statins, and as a fixed combination with simvastatin. In December 2001, Merck and SP expanded their partnership launched in the US in 2000, to develop and market ezetimibe. In August and September 2001, Credit Suisse First Boston predicted ezetimibe sales of US $420 million in 2003 and US $959 million in 2004. Analysts at Salomon Smith Barney predicted in November 2001 that the product would be launched in 2003.

Synthesis of iodinated biochemical tools related to the 2-azetidinone class of cholesterol absorption inhibitors

The discoveries of Sch 48461 and Sch 58235 and their novel pharmacology of inhibition of cholesterol absorption have prompted efforts to determine their biological mechanism of action (MOA). To this end, a series of radioiodinated analogues with good to excellent in vivo activity have been designed and synthesized as single enantiomers. They are structurally consistent with the allowable SAR of the 2-azetidinone class of cholesterol absorption inhibitors.

Reinvestigation of the iodocyclization of 4,5,7-tri-O-benzyl-3-(N-benzylacetamido)-1,2,3-trideoxy-D-gluco-hept-1-enitol: unexpected formation of a 1,3-imino-heptitol derivative

The NIS-mediated iodocyclization of 4,5,7-tri-O-benzyl-3-(N-benzylacetamido)-1,2,3-trideoxy-D-gluco-hept-1-enitol gave unexpectedly a 1,3-imino-heptitol derivative, namely 2-O-acetyl-N-benzyl-4,5,7-tri-O-benzyl-1,3-dideoxy-1,3-imino-D-glycero-D-ido-heptitol. This compound is a new example of a rare class of azetidine imino alditol derivatives which have interesting properties such as glycosidase inhibitors. The physical and spectral data for this imino heptitol were essentially identical to those reported for 2,6-anhydro-4,5,7-tri-O-benzyl-3-(N-benzylacetamido)-3-deoxy-D-glycero-D-ido-heptitol, a derivative of C-(2-acetamido-2-deoxy-alpha-D-glucopyranosyl)methanol obtained from the same precursor [Lay, L.; Nicotra, F.; Panza, L.; Verani, A. Gazz. Chim. Ital. 1992, 122, 345-348]; these findings cast doubts on the structure reported for the latter product.

Synthesis of ferrocene-substituted 2-azetidinones

The photochemical reaction of alkoxychromium(0)carbene complexes and ferrocene mono- and disubstituted imines formed 2-azetidinones having one or two ferrocene moieties in good yields. Yields decrease when the carbene moiety bears an aminoferrocene moiety attached to the carbene carbon, while complex 9 having the ferrocene directly bonded to the carbene carbon was totally inert in these reactions. Access to beta-lactams with the ferrocene tethered to the C3 position through a methylene group was gained using the lithium enolate derived from ethyl 3-ferrocenylpropanoate. The reaction of this enolate produced two unexpected processes. Thus, 2-azetidinone 15 having an hydroxyl group at the C3 position was obtained together with the expected beta-lactam 14, by reaction of the lithium enolate of ethyl 3-ferrocenylpropenoate and imine 1. Additionally, unsaturated amide 17 was obtained by base-promoted Hoffmann-like breakage of the beta-lactam ring formed in the reaction of the same enolate and imine 2. Oxidation of the anion at the C3 of the 2-azetidinone ring on compound 14, as well as the sterically driven ring-breakage of the C3 anion derived from the nonisolated 2-azetidinone 18, should be responsible for this behavior.

Design, synthesis and pharmacological evaluation of 3-benzylazetidine-2-one-based human chymase inhibitors

3-Benzylazetidine-2-one derivatives were designed and evaluated as a novel series of chymase inhibitors. Structure-activity relationship studies of 3-benzylazetidine-2-ones led to compounds 23, which exhibited 3.1 nM inhibition of human chymase and enhancement of stability in human plasma (t(1/2) 6h).

[Development of aziridination and azetizination reactions of amino allenes using a palladium catalyst]

Palladium-catalyzed synthesis of alkenylaziridines and azetidines from alpha- and beta-amino allenes are presented. Whereas palladium-catalyzed reaction of N-arylsulfonyl-alpha-amino allenes with an aryl iodide in the presence of potassium carbonate in DMF at around 70 degrees C affords the corresponding 3-pyrroline derivatives, the reaction in refluxing 1,4-dioxane under similar conditions yields exclusively or most predominantly the corresponding 2-alkenylaziridines bearing an aryl group on the double bond. Similarly, N-arylsulfonyl-beta-amino allenes can be also cyclized into the corresponding alkenylazetidines bearing 2,4-cis-sunstituents under palladium-catalyzed cyclization conditions in DMF.

Metal-promoted allylation, propargylation, or allenylation of azetidine-2,3-diones in aqueous and anhydrous media. Application to the asymmetric synthesis of densely functionalized 3-substituted 3-hydroxy-beta-lactams

Metal-mediated carbonyl allylation, allenylation, and propargylation of optically pure azetidine-2,3-diones were investigated in both anhydrous and aqueous environments. Different metals promoters showed varied regioselectivities on product formation during allenylation/propargylation reactions of the keto-beta-lactams. The stereochemistry of the new C3-substituted C3-hydroxy quaternary center was controlled by placing a chiral auxiliary at C4. In this way, the coupling of azetidine-2,3-diones with a variety of propenyl-, propynyl-, and allenylmetal reagents offers a convenient asymmetric entry to potentially bioactive 3-substituted 3-hydroxy-beta-lactams.

Design, synthesis, and proposed active site binding analysis of monocyclic 2-azetidinone inhibitors of prostate specific antigen

A homology derived molecular model of prostate specific antigen (PSA) was created and refined. The active site region was investigated for specific interacting functionality and a binding model postulated for the novel 2-azetidinone acyl enzyme inhibitor 1 (IC(50) = 8.98 +/- 0.90 microM) which was used as a lead compound in this study. A single low energy conformation structure II (Figure 2) was adopted as most likely to represent binding after minimization and dynamics calculations. Systematic analysis of the binding importance of all three side chains appended to the 2-azetidinone was conducted by the synthesis of several analogues. A proposed salt bridge to Lys-145 with 4 (IC(50) = 5.84 +/- 0.92 microM) gave improved inhibition, but generally the binding of the N-1 side chain in a specific secondary aromatic binding site did not tolerate much structural alteration. A hydrophobic interaction of the C-4 side chain afforded inhibitor 6 (IC(50) = 1.43 +/- 0.19 microM), and polar functionality could also be added in a proposed interaction with Gln-166 in 5 (IC(50) = 1.34 +/- 0.05 microM). Reversal of the C-4 ester connectivity furnished inhibitors 7 (IC(50) = 1.59 +/- 0.15 microM), 11 (IC(50) = 3.08 +/- 0.41 microM), and 13 (IC(50) = 2.19 +/- 0.36 microM) which were perceived to bind to PSA by a rotation of 180 degrees relative to the C-4 ester of normal connectivity. Incorporation of hydroxyl functionality into the C-3 side chain provided 16 (IC(50) = 348 +/- 50 nM) with the greatest increase in PSA inhibition by a single modification. Multiple copy simultaneous search (MCSS) analysis of the PSA active site further supported our model and suggested that 18 would bind strongly. Asymmetric synthesis yielded 18 (IC(50) = 226 +/- 10 nM) as the most potent inhibitor of PSA reported to date. It is concluded that our design approach has been successful in developing PSA inhibitors and could also be applied to the inhibition of other enzymes, especially in the absence of crystallographic information.

Design, synthesis and stability of N-acyloxymethyl- and N-aminocarbonyloxymethyl-2-azetidinones as human leukocyte elastase inhibitors

A series of N-acyloxymethyl- and N-aminocarbonyloxymethyl derivatives of 2-azetidinones, 3, with different substituent patterns at the beta-lactam C-3 and C-4 positions, were designed as potential mechanism-based inhibitors for human leukocyte elastase and found to exhibit inhibitory potency and selectivity for the enzyme.