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Objectives LK-157 is a novel 10-ethylidene tricyclic carbapenem that resembles the structure of the broad-spectrum antibiotic sanfetrinem and acts as a potent inactivator of β-lactamases of classes A, C and D. LK-157 is a highly soluble but poorly permeable drug. Since most of the β-lactams are poorly absorbed, ester prodrugs LK-159, LK-157E1 and LK-157E2 were designed to enhance membrane permeability. This study investigated the permeability of LK-157 and the three ester prodrugs across rat intestine in vitro. The morpholinoethyl ester of sanfetrinem was also investigated. Method Permeability across rat jejunum was determined using EasyMount side-by-side diffusion chambers. Key findings The solubility and permeability of morpholinoethyl ester LK-157E2 were superior to those of LK-159 and LK-157E1. The morpholinoethyl ester of sanfetrinem LK-176E1 had the highest observed permeability coefficient and consequently the highest predicted absorption in humans. Conclusions These results suggest that the morpholinoethyl esters of LK-157 and sanfetrinem could be further investigated to assess bioavailability in vivo.

Cycloadditions of various 1,3-dipoles to methyl (S)-1-tert-butoxycarbonyl-3-[(E)-cyanomethylidene]-2-pyrrolidinone-5-carboxylate (9) were studied. Reactions of 9 with diazomethane (10) and 2,4,6-trimethoxy-benzonitrile oxide (11), carried out under neutral conditions, gave the corresponding optically active spiro compounds 16-18 with low diastereoselectivity (20-30% diastereomeric excess). On the other hand, reactions of 9 with nitrile oxide 11 and nitrile imines 14, 15, carried out in the presence of a base, afforded racemic pyrazolo and isoxazolo fused 2-pyrrolidinones 21-23 in 82-86% diastereomeric excess. Optically active dipolarophile 9 was isomerized in the presence of basic alumina to give methyl (RS)-1-tert-butoxy-carbonyl-3-cyanomethyl-1,2-dihydro-2-oxo-5H-pyrrole-5-carboxylate (19). Treatment of the racemic dipolarophile 19 with dipoles 11 and 14, afforded fused 2-pyrrolidinones 23 and 21. These observations support compound 19 as the key-intermediate in the formation of racemic cycloadducts 21-23.

Known carbapenem compounds with inhibitory effect towards beta-lactamase enzymes are formed from bicyclical beta lactam structural scaffolds. On the basis of results from theoretical computational methods and molecular modelling we have designed and developed a synthetic route towards novel, biologically active tricyclic derivatives of carbapenems.

Reactions of dimethyl 5-aryl-2,3-dihydro-3,3-dimethyl-1-oxo-1H,5H-pyrazolo[1,2–a]pyrazole6,7-dicarboxylates 3a–e with excess of hydrazine hydrate gave propanohydrazides 5a–e in 70– 99% yields. The ring opening of pyrazolo[1,2–a]pyrazole-6,7-dicarboxylates 3a–e proceeded stereoselectively, furnishing the rel-(4'R,5'S)-isomers of 3-[5-aryl-3,4-bis(hydrazinocarbonyl)4,5-dihydro-1H-pyrazol-1-yl)-3-methyl-butanohydrazides 5a–e. The X–ray structure of 5a was determined.

Some new six-membered aplysinopsin analogues were prepared from 5-dimethylaminomethylidene-2,4,6(1H,3H,5H)-pyrimidinetriones and indole derivatives. Also 2-[[(2,4,6-trioxohexahydropyrimidin-5-ylidene)methyl]amino]-3-dimethylaminopropenoates were synthesized and employed in the synthesis of fused 2H-pyran-2-ones.

The 5,5-dimethylpyrazolidin-3-one (4), prepared from ethyl 3-methylbut-2-enoate (3) and hydrazine hydrate, was treated with various substituted benzaldehydes 5a – i to give the corresponding (1Z)-1-(arylmethylidene)-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide azomethine imines 6a – i. The 1,3-dipolar cycloaddition reactions of azomethine imines 6a – h with dimethyl acetylenedicarboxylate (=dimethyl but-2-ynedioate; 7) afforded the corresponding dimethyl pyrazolo[1,2-a]pyrazoledicarboxylates 8a – h, while by cycloaddition of 6 with methyl propiolate (=methyl prop-2-ynoate; 9), regioisomeric methyl pyrazolo[1,2-a]pyrazolemonocarboxylates 10 and 11 were obtained. The regioselectivity of cycloadditions of azomethine imines 6a – i with methyl propiolate (9) was influenced by the substituents on the aryl residue. Thus, azomethine imines 6a – e derived from benzaldehydes 5a – e with a single substituent or without a substituent at the ortho-positions in the aryl residue, led to mixtures of regioisomers 10a – e and 11a – e. Azomethine imines 6f – i derived from 2,6-disubstituted benzaldehydes 5f – i gave single regioisomers 10f – i.

A simple stereoselective synthesis of 2Z and 2Z,1′E alkyl 3-acyloxy-2-(2,2-disubstituted ethenyl) aminopropenoates 4 from alkyl 2-(2,2-disubstituted ethenyl)amino-3-dimethylaminopropenoates 1 in 12–91% yield is presented.

Simple and stereoselective syntheses of aplysinopsins and their analogs from either methyl 2-[(2,2-disubstituted ethenyl)amino]-3-(dimethylamino)prop-2-enoates 11 or 5-[(dimethylamino)methylidene]imidazolidine-2,4-diones 20 are described. The structures of products are established by 1H- and 13C-NMR, and NOESY spectroscopy, and X-ray crystal-structure analysis.

Methyl 2-[bis(acetyl)ethenyl]aminopropenoate (4) was prepared in 3 steps from acetylacetone (1) via 4-(N,N-dimethylamino)-3-acetylbut-3-en-2-one (2) and methyl N-[2,2-bis(acetyl)ethenyl]glycinate (3). Compound 4 reacts with N- and C-nucleophiles to give fused heterocyclic systems. Derivatives of pyrido[1,2-a]pyrimidones 14–16 and thiazolo[3,2-a]pyrimidones 17 and 18 were prepared from 2-aminopyridines and 2-aminothiazoles, respectively. With C-nucleophiles derivatives of pyrido[1,2-a]-pyridinone 19 and 2H-1-benzopyran-2-one 20–22 were prepared.

Methyl 2-[bis(acetyl)ethenyl]aminopropenoate (4) was prepared in 3 steps from acetylacetone (1) via 4-(N,N-dimethylamino)-3-acetylbut-3-en-2-one (2) and methyl N-[2,2-bis(acetyl)ethenyl]glycinate (3). Compound 4 reacts with N- and C-nucleophiles to give fused heterocyclic systems. Derivatives of pyrido[1,2-a]pyrimidones 14–16 and thiazolo[3,2-a]pyrimidones 17 and 18 were prepared from 2-aminopyridines and 2-aminothiazoles, respectively. With C-nucleophiles derivatives of pyrido[1,2-a]-pyridinone 19 and 2H-1-benzopyran-2-one 20–22 were prepared.

Transformations of intermediates 4, prepared from methyl 2-(2,2-disubstituted-ethenyl)amino-3-dimethylaminopropenoates 2 and sterically hindered heteroarylamines 3, into methyl 1-heteroaryl-1H-imidazole-4-carboxylates 7 are described.

[reaction: see text] Reaction of 5,5-dimethyl-3-pyrazolidinone (1) with 2-indanone (2) gave 5,5-dimethyl-2-(1H-indenyl-2)-3-pyrazolidinone (3) instead of the expected azomethine imine 4. Although reaction of 2-substituted 3-pyrazolidinones with acetylenedicarboxylates usually gives ring expansion products, such as 1,2-diazepines, treatment of 3 with dialkyl acetylenedicarboxylates (5, R = Me; 6 R = Et) resulted in the formation of rel-(7aR,12aS)-6,7-bis(alkoxycarbonyl)-3,4-dihydro-4,4-dimethyl-7aH-indano[1,2-b]pyrrolo[1,2-a]pyrimidin-2-ones (7, R = Me; 9, R = Et) as major products and 3,4-bis(alkoxycarbonyl)-7,7-dimethyl-2-(indenyl-2)-6,7-dihydro-2H,6H-1,2-diazepin-5-ones (8, R = Me: 10, R = Et) as minor products.

A simple stereoselective synthesis of 2Z and 2Z,1′E alkyl 3-acyloxy-2-(2,2-disubstituted ethenyl) aminopropenoates 4 from alkyl 2-(2,2-disubstituted ethenyl)amino-3-dimethylaminopropenoates 1 in 12–91% yield is presented.

LK-157 is a novel 10-ethylidene tricyclic carbapenem that resembles the structure of the broad-spectrum antibiotic sanfetrinem and acts as a potent inactivator of beta-lactamases of classes A, C and D. LK-157 is a highly soluble but poorly permeable drug. Since most of the beta-lactams are poorly absorbed, ester prodrugs LK-159, LK-157E1 and LK-157E2 were designed to enhance membrane permeability. This study investigated the permeability of LK-157 and the three ester prodrugs across rat intestine in vitro. The morpholinoethyl ester of sanfetrinem was also investigated.Permeability across rat jejunum was determined using EasyMount side-by-side diffusion chambers.The solubility and permeability of morpholinoethyl ester LK-157E2 were superior to those of LK-159 and LK-157E1. The morpholinoethyl ester of sanfetrinem LK-176E1 had the highest observed permeability coefficient and consequently the highest predicted absorption in humans.These results suggest that the morpholinoethyl esters of LK-157 and sanfetrinem could be further investigated to assess bioavailability in vivo.

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.

Transformations of intermediates 4, prepared from methyl 2-(2,2-disubstituted-ethenyl)amino-3-dimethylaminopropenoates 2 and sterically hindered heteroarylamines 3, into methyl 1-heteroaryl-1H-imidazole-4-carboxylates 7 are described.

Cycloadditions of various 1,3-dipoles to methyl (S)-1-tert-butoxycarbonyl-3-[(E)-cyanomethylidene]-2-pyrrolidinone-5-carboxylate (9) were studied. Reactions of 9 with diazomethane (10) and 2,4,6-trimethoxy-benzonitrile oxide (11), carried out under neutral conditions, gave the corresponding optically active spiro compounds 16-18 with low diastereoselectivity (20-30% diastereomeric excess). On the other hand, reactions of 9 with nitrile oxide 11 and nitrile imines 14, 15, carried out in the presence of a base, afforded racemic pyrazolo and isoxazolo fused 2-pyrrolidinones 21-23 in 82-86% diastereomeric excess. Optically active dipolarophile 9 was isomerized in the presence of basic alumina to give methyl (RS)-1-tert-butoxy-carbonyl-3-cyanomethyl-1,2-dihydro-2-oxo-5H-pyrrole-5-carboxylate (19). Treatment of the racemic dipolarophile 19 with dipoles 11 and 14, afforded fused 2-pyrrolidinones 23 and 21. These observations support compound 19 as the key-intermediate in the formation of racemic cycloadducts 21-23.

The 5,5-dimethylpyrazolidin-3-one (4), prepared from ethyl 3-methylbut-2-enoate (3) and hydrazine hydrate, was treated with various substituted benzaldehydes 5a – i to give the corresponding (1Z)-1-(arylmethylidene)-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ide azomethine imines 6a – i. The 1,3-dipolar cycloaddition reactions of azomethine imines 6a – h with dimethyl acetylenedicarboxylate (=dimethyl but-2-ynedioate; 7) afforded the corresponding dimethyl pyrazolo[1,2-a]pyrazoledicarboxylates 8a – h, while by cycloaddition of 6 with methyl propiolate (=methyl prop-2-ynoate; 9), regioisomeric methyl pyrazolo[1,2-a]pyrazolemonocarboxylates 10 and 11 were obtained. The regioselectivity of cycloadditions of azomethine imines 6a – i with methyl propiolate (9) was influenced by the substituents on the aryl residue. Thus, azomethine imines 6a – e derived from benzaldehydes 5a – e with a single substituent or without a substituent at the ortho-positions in the aryl residue, led to mixtures of regioisomers 10a – e and 11a – e. Azomethine imines 6f – i derived from 2,6-disubstituted benzaldehydes 5f – i gave single regioisomers 10f – i.

[reaction: see text] Reaction of 5,5-dimethyl-3-pyrazolidinone (1) with 2-indanone (2) gave 5,5-dimethyl-2-(1H-indenyl-2)-3-pyrazolidinone (3) instead of the expected azomethine imine 4. Although reaction of 2-substituted 3-pyrazolidinones with acetylenedicarboxylates usually gives ring expansion products, such as 1,2-diazepines, treatment of 3 with dialkyl acetylenedicarboxylates (5, R = Me; 6 R = Et) resulted in the formation of rel-(7aR,12aS)-6,7-bis(alkoxycarbonyl)-3,4-dihydro-4,4-dimethyl-7aH-indano[1,2-b]pyrrolo[1,2-a]pyrimidin-2-ones (7, R = Me; 9, R = Et) as major products and 3,4-bis(alkoxycarbonyl)-7,7-dimethyl-2-(indenyl-2)-6,7-dihydro-2H,6H-1,2-diazepin-5-ones (8, R = Me: 10, R = Et) as minor products.

Stereospecific conversions of dimethylaminomethylidene group in various (Z)-alkyl 2-[(2,2-disubstituted ethenyl)amino]-3-dimethylaminopropenoates into their hydroxymethylidene and benzoyloxy methylidene derivatives were achieved in moderate to good yields. The difference between pathway to enol esters and (fused)pyrrole-2-carboxylate derivatives is clarified.

5-(2-Phenyl-1H-indol-3-ylmethylene)-2-thioxoimidazolidin-4-one (2) and its oxo derivatives as well as some novel 5-bromoaplysinopsin analogues were synthesized employing dimethylamine substitution in N,N-dimethyl-methylideneimidazolidinones (6).

Methyl 2-acetyl-3-{[2-(dimethylamino)-1-(methoxycarbonyl)ethenyl]amino}prop-2-enoate (4) and phenyl-methyl 2-acetyl-3-{[2-(dimethylamino)-1(methoxycarbonyl)ethenyl]amino}prop-2-enoate (5) were prepared in three steps from the corresponding acetoacetic esters, and used as reagents for the preparation of N3-protected 3-amino-4H-pyrido[1,2-a]pyrimidin-4-ones 10–12, 5H-thiazolo[3,2-a]pyrimidin-5-one 13, 4H-pyrido[1,2-a]-pyridin-4-one 19 and 2H-1-benzopyran-2-ones 20–23. Free 3-amino-4H-pyrido[1,2-a]pyrimidin-4-ones 24–26 were prepared from 10–12 by removal of the 2-(methoxycarbonyl)-3-oxobut-1-enyl or 3-oxo-2-[(phenyl-methoxy)carbonyl]but-1-envl as N-protecting group by various methods.