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The clinical treatment of multifactorial pathologies (e.g. cancer, Alzheimer’s disease, psychiatric disorders), is still a major challenge. Many researches have been published dealing with the design of multiple ligands, able to act at the same time towards several targets relevant for a given pathology. In the present review, the clinical results about these compounds have been reported, together with the design strategy adopted, in order to allow a critical evaluation of the outcomes of these efforts. What is emerging is that several effective design strategies of multitarget compounds are available, and the choice among these appears to be dependent on the therapeutic area considered. However, at present, besides multitarget drugs discovered during optimization efforts by means of phenotypic assays, drug coadministrations or fixed dose formulations appear to be more useful therapeutic options than designed multiple ligands; this scenario will change when systems biology will be able to select critical targets, i.e. nodal proteins that should be inhibited in order to obtain a therapeutic action; at this point, the design of multiple ligands will allow a renaissance of medicinal chemistry.

SSAO/VAP-1 is not only involved in the metabolism of biogenic and xenobiotic primary amines and in the production of metabolites with cytotoxic effects or certain physiological actions, but also plays a role, for example, as an adhesion molecule, in leukocyte trafficking, in regulating glucose uptake and in adipocyte homeostasis. Interest in the enzyme has been stimulated by the findings that the activities of the SSAOs are altered (mostly increased) in various human disorders, including diabetes, congestive heart failure, liver cirrhosis, Alzheimers disease and several inflammatory diseases, although the underlying causes are often unknown. On the basis of their insulin-mimicking effect, SSAO substrates are possibly capable of ameliorating metabolic changes in diabetes, while SSAO inhibitors (somewhat of a contradiction) are of potential benefit in preventing diabetes complications, atherosclerosis and oxidative stress contributing to several disorders or modulating inflammation, and hence may be of substantial therapeutic value. Great efforts have been made to develop novel compounds which may lead to future drugs useful in therapy, based on their effects on SSAO/VAP-1, and some of the results relating to novel substrates and inhibitors are surveyed in the present review.

Mono- and diphenylpyridazine ureido derivatives, structurally related to DuP 128, were synthesized and tested for their inhibitory activity against ACAT isolated from rat liver microsomes. Several compounds displayed ACAT inhibition in the micromolar range. The amino derivatives 4a−c were also tested against hACAT-1 and hACAT-2 isoforms. They retained the same trend shown in the previous assay. Modeling studies on representative terms were performed. Significant similarities between the geometrical features of the model DuP 128 and the most active pyridazine derivatives were observed.

Recent methodologies applied to the drug discovery process, such as genomics and proteomics, have greatly implemented our basic understanding of drug action and are giving more input to medicinal chemists, in finding genuinely new targets and opportunities for the development of drugs with original mechanisms of action. In this paper, an example of the successful application of some new techniques to the target enzymes with the Thymidylate Synthase (TS) function is given. The improved knowledge of the complex mechanism of the biological pathways in which thymidylate synthase is involved represents a unique chance to find new mechanism-based inhibitors, aimed to treat not only cancerous diseases, but also infectious pathologies. Thymidylate synthase (TS or ThyA) has long been considered as one of the best-known drug targets in the anti-cancer area, after which old and new drugs, such as 5-fluoro uracil and the anti-folate ZD1694, have been introduced into chemotherapy to treat solid tumours. Only a few attempts have been made to find non-classical anti-folate inhibitors that are dissimilar to the folate co-factor, with the aim of finding unshared protein target domains on the enzyme structure, in order to specifically inhibit TS enzymes from pathogens. Only recently from omic studies, a new Thymidylate Synthase Complementing Protein (TSCP or ThyX) has been identified in a number of pathogens, showing a different structure with respect to human TS, thus opening new avenues to specific inhibitions. A depiction of the most recent progress in the study of Thymidylate Synthase enzymes is presented in the following sections.

The concept of convergent synthesis can be extended to combinatorial chemistry in order to obtain collections of products characterized by considerable chemical diversity and a certain molecular complexity. In this work, a library consisting of three carboxylic acids containing a benzimidazolonic functionality with variations at two positions was synthesized on solid phase. After cleavage, this library was combined with a second library consisting of 16 solid-supported amines containing two points of variation. IRORI technology was used for the split-and-mix synthesis of the final 48 members library.

Semicarbazide-sensitive amine-oxidase (SSAO) is present in various human tissues and in plasma. Oxidative deamination of short-chain aliphatic amines is catalyzed by this enzyme to afford the corresponding aldehydes, ammonia and hydrogen peroxide. Methylamine and aminoacetone have been recognized to be physiological substrates for SSAO. There are several pathological states where increased serum SSAO activity have been found, such as diabetes mellitus, congestive heart failure, multiple types of cerebral infarction, uraemia, and hepatic cirrhosis. The role of SSAO in pathophysiology of diabetes has been most extensively investigated. The elevated formation of the potentially cytotoxic products of the enzyme may contribute to the endothelial injury of blood vessels, resulting in the early development of severe atherosclerosis it may also contribute to the pathogenesis of diabetic angiopathy. It is now suggested that SSAO inhibitors may prevent the development of atherosclerosis and diabetic complications as well. Inhibitors can be conveniently subdivided into the main groups of hydrazine derivatives, arylalkylamines, propenyl- and propargylamines, oxazolidinones, and haloalkylamines. Of them, aryl(alkyl)hydrazines, and 3-halo-2-phenylallylamines are generally very strong SSAO inhibitors. Most of these inhibitors of SSAO have been originally developed for other purposes, or they are simple chemical reagents with highly reactive structural element(s) these compounds have not been able to fulfil all criteria of high potency, selectivity, and acceptable toxicity. New potent compounds with selectivity and low toxicity are needed, which may prove useful tools for understanding the roles and function of SSAO, or they may even be valuable substances for treatment of various diseases.

In the present study, more than 75 compounds structurally related to BMY 7378 have been designed and synthesized. Structural variations of each part of the reference molecule have been introduced, obtaining highly selective ligands for the α1d adrenergic receptor. The molecular determinants for selectivity at this receptor are essentially held by the phenyl substituent in the phenylpiperazine moiety. The integration of an extensive SAR analysis with docking simulations using the rhodopsin-based models of the three α1-AR subtypes and of the 5-HT1A receptor provides significant insights into the characterization of the receptor binding sites as well as into the molecular determinants of ligand selectivity at the α1d-AR and the 5-HT1A receptors. The results of multiple copies simultaneous search (MCSS) on the substituted phenylpiperazines together with those of manual docking of compounds BMY 7378 and 69 into the putative binding sites of the α1a-AR, α1b-AR, α1d-AR, and the 5-HT1A receptors suggest that the phenylpiperazine moiety would dock into a site formed by amino acids in helices 3, 4, 5, 6 and extracellular loop 2 (E2), whereas the spirocyclic ring of the ligand docks into a site formed by amino acids of helices 1, 2, 3, and 7. This docking mode is consistent with the SAR data produced in this work. Furthermore, the binding site of the imide moiety does not allow for the simultaneous involvement of the two carbonyl oxygen atoms in H-bonding interactions, consistent with the SAR data, in particular with the results obtained with the lactam derivative 128. The results of docking simulations also suggest that the second and third extracellular loops may act as selectivity filters for the substituted phenylpiperazines. The most potent and selective compounds for α1d adrenergic receptor, i.e., 69 (Rec 26D/038) and 128 (Rec 26D/073), are characterized by the presence of the 2,5-dichlorophenylpiperazine moiety.

Inhibition of ACAT, the enzyme which catalyses the intracellular formation of cholesteryl esters, is a very attractive target for the treatment of hypercholesterolaemia and atherosclerosis. However, in the past years many ACAT inhibitors gave disappointing results in clinical trials showing very low efficacy. In addition, their development was affected by the adrenotoxicity observed in many compounds. The discovery of two isoforms of the enzyme, namely ACAT1 and ACAT2, with different substrate specificity and different potential function, offers a precious information for planning selective inhibitors with reduced secondary effects. Today some potent, bioavailable and non adrenotoxic ACAT inhibitors are under clinical evaluation. Amongst others, a very promising compound is Avasimibe, presently in phase III clinical trials as anti-hyperlipidemic and anti-atherosclerotic agent. Finally, ACAT inhibitors have recently been proposed for the treatment of Alzheimer's disease.

3,8-Diazabicyclo[3.2.1]octane (1), 2,5-diazabicyclo[2.2.1]heptane (2), piperazine (3), and homopiperazine (4) derivatives, substituted at one nitrogen atom with the 6-chloro-3-pyridazinyl group while the other nitrogen atom was either unsubstituted or mono- or dimethylated, were synthesized and tested for their affinity toward the neuronal nicotinic acetylcholine receptors (nAChRs). All of the compounds had Ki values in the nanomolar range. A molecular modeling study allowed location of their preferred conformations, the energies of which were recalculated in water with a continuum solvent model. Some of the compounds showed, in their populated conformations, only pharmacophoric distances longer than the values taken into consideration by the Sheridan model for nAChRs receptors. Thus, this SAR study gives support to the hypothesis that these longer distances are still compatible with affinity for α4β2 receptors in the nanomolar range.

In accordance with the title of my lecture, I am going to briefly illustrate our researches on pyridazine derivatives active in different biological areas.

Opioid receptor like-1 (ORL-1) has recently been indicated as a potentially useful target for the treatment of a number of central disorders and several other diseases. This review deals with non-peptidic ligands at the ORL-1 receptor, focusing on their structural and binding properties. Agonism or antagonism evidenced from functional experiments is also commented. For some compounds, possible therapeutic applications are considered.

Alkyl-5,6-diphenylpyridazine derivatives combining several main features of ACAT inhibitors, such as a long alkyl side chain linked to a heterocycle and the o-diphenyl system, were synthesized and tested. Moreover, modeling studies on representative terms were performed. Some compounds displayed ACAT inhibition in the micromolar range, both on the enzyme isolated from rat liver microsomes and in cell-free homogenate of murine macrophages.

QSAR models have been used for designing a series of compounds characterized by a N-phenylpiperazinylalkylamino moiety linked to substituted pyridazinones, which have been synthesized. Measurements of the binding affinities of the new compounds toward the α1a-, α1b-, and α1d-AR cloned subtypes as well as the 5-HT1A receptor have been done validating, at least in part, the estimations of the theoretical models. This study provides insight into the structure activity relationships of the α1-ARs ligands and their α1-AR/5-HT1A selectivity.

A new set of phthalein derivatives stemming from the lead compound, phenolphthalein, were designed to specifically complement structural features of a bacterial form of thymidylate synthase (Lactobacillus casei, LcTS) versus the human TS (hTS) enzyme. The new compounds were screened for their activity and their specificity against TS enzymes from different species, namely, L. casei (LcTS), Pneumocystis carinii (PcTS), Cryptococcus neoformans (CnTS), and human thymidylate synthase (hTS). Apparent inhibition constants (Ki) for all the compounds against LcTS were determined, and inhibition factors (IF, ratio between the initial rates of the enzymatic reaction in the presence and absence of each inhibitor) against each of the four TS species were measured. A strong correlation was found between the two activity parameters, IF and Ki, and therefore the simpler IF was used as a screening factor in order to accelerate biological evaluation. Compounds 5b, 5c, 5ba, and 6bc showed substantial inhibition of LcTS while remaining largely inactive against hTS, illustrating for the first time remarkable species specificity among TSs. Due to sequence homology between the enzymes, several compounds also showed high activity and specificity for CnTS. In particular, 3-hydroxy-3-(3-chloro-4-hydroxyphenyl)-6-nitro-1H,3H-naphtho[1,8-c,d]pyran-1-one (6bc) showed an IF < 0.04 for CnTS (Ki = 0.45 μM) while remaining inactive in the hTS assay at the maximum solubility concentration of the compound (200 μM). In cell culture assays most of the compounds were found to be noncytotoxic to human cell lines but were cytotoxic against several species of Gram-positive bacteria. These results are consistent with the enzymatic assays. Intriguingly, several compounds also had selective activity against Cr. neoformans in cell culture assay. In general, the most active and selective compounds against the Gram-positive bacteria were those designed and found in the enzyme assay to be specific for LcTS versus hTS. The original lead compound was least selective against most of the cell lines tested. To our knowledge these compounds are the first TS inhibitors selective for bacterial TS with respect to hTS.

The isoxazolo-[3,4-d]-pyridazin-7-(6H)-one (2) and its corresponding open derivatives 5-acetyl-4-amino-(4-nitro)-6-substituted-3(2H)pyridazinones (3, 4) were used as simplified substrates for the synthesis of new aldose reductase inhibitors with respect to the previously reported 5,6-dihydrobenzo[h]cinnolin-3(2H)one-2 acetic acids (1). Moreover, a few derivatives lacking the 5-acetyl group were prepared. Several compounds derived from 2 displayed inhibitory properties comparable to those of Sorbinil. In this class the presence at position 6 of a phenyl carrying an electron-withdrawing substituent proved to be beneficial, independently from its position on the ring (5g,j−l). Acetic acid derivatives were more effective than propionic and butyric analogues. On the contrary, all the monocyclic compounds (6−8) were either inactive or only weakly active. The 3-methyl-4-(p-chlorophenyl)isoxazolo-[3,4-d]-pyridazin-7-(6H)-one acetic acid (5g), which proved to be the most potent derivative, was also investigated in molecular modeling studies, to assess possible similarities in its interaction with the enzyme, with respect to the model 1.

A still unknown tricyclic heterocyclic system (5) was synthesized from 6-hydroxy-2-methylpyridazin-3-one and its structure identified as 2,8-dichloro-6-methylpyrrolo[1,2-b:3,4-d‘]dipyridazin-5(6H)-one by spectroscopic investigations. Selective condensation of 5 with 2-[4-(2-substituted-phenyl)piperazin-1-yl]ethylamine gave the 2-arylpiperazinylethylamino-8-chloro derivatives 6a−c, which were investigated in binding studies toward the three α1-adrenergic and 5-HT1A-serotonergic receptor subtypes. They displayed high potency on all the assays and some selectivity for α1a and α1d subtypes.

The present study investigates the antisecretory and antiulcer mechanisms of a new indenopyridazinone derivative previously reported to inhibit gastric acid secretion in pylorus-ligated rats and to prevent gastric ulcerations induced by indomethacin or ethanol in the same animal species. The new compound was tested on the acid hypersecretion induced by histamine, pentagastrin and bethanechol inin vivoandin vitroexperimental models. Furthermore, its influence on the mucosal layer adhering the gastric wall in indomethacin-treated rats was considered. Ranitidine was selected as a reference drug. The results obtained demonstrated that the new molecule, at variance with ranitidine, exerts antiulcer activity mainly enhancing the gastric mucosal integrity and simultaneously inhibiting the gastric acid hypersecretion evoked exclusively by cholinergic pulses. Therefore, an involvement of a neuronal rather than an effectorial mechanism has been suggested. Due to these mechanisms of action it clearly differentiates from ranitidine and its possible application in the peptic disease resistant to H2-blockers could be speculated.

A new series of analogues (1c–j; 2c–i) of the previously reported analgesic 3,8-diazabicyclo[3.2.l]octanes (1a,b; 2a,b) was synthesized and tested for their affinity towards μ-opioid receptors. Modifications were introduced either at the cinnamyl or the acyl side chains. The majority of the new compounds, with the exception of 1c,jand 2c, showed Kivalues better or comparable with those of the models.

A series of 2-substituted 4,5-functionalized 6-phenyl-3(2 H )-pyridazinones were synthesized and their antinociceptive activities were evaluated in the mouse abdominal constriction model. Single dose studies showed that compounds 11, 18a and 23 were more active than the reference drug, Emorfazone, in inhibiting the effects of the noxious chemical stimulus, p -phenylquinone. Subsequent dose--response studies revealed 18a to be almost seven-fold more potent than Emorfazone.

A series of 3,8-diazabicyclo[3.2.1]octanes substituted either at the 3 position (compounds 1) or at the 8 position (compounds 2) by a chlorinated heteroaryl ring were synthesized, as potential analogues of the potent natural analgesic epibatidine. When tested in the hot plate assay, the majority of the compounds showed significant effects, the most interesting being the 3-(6-chloro-3-pyridazinyl)-3,8-diazabicyclo[3.2.1]octane (1a). At a subcutaneous dose of 1 mg/kg, 1a induced a significant increase in the pain threshold, its action lasting for about 45 min. 1a also demonstrated good protection at a dose of 5 mg/kg in the mouse abdominal constriction test, while at 20 mg/kg it completely prevented the constrictions in the animals. Administration of naloxone (1 mg/kg ip) did not antagonize its antinociception while mecamylamine (2 mg/kg ip) did, thus suggesting the involvement of the nicotinic system in its action. Binding studies confirmed high affinity for the α4β2 nAChR subtype (Ki = 4.1 ± 0.21 nM). nAChR functional activity studies on three different cell lines showed that 1a was devoid of any activity at the neuromuscular junction. Finally, due to the analogy in their pharmacological profile with that of epibatidine, compounds were compared from a structural and conformational point of view through theoretical calculations and high-field ¹H NMR spectroscopy. Results indicate that all of them present one conformation similar to that of epibatidine.

Three new series of tricyclic pyridazinones have been synthesized and tested in vitro in order to assess (i) their ability to inhibit aldose reductase enzyme (ALR2) and (ii) their specificity toward the target enzyme with respect to other related oxidoreductases, such as aldehyde reductase, sorbitol dehydrogenase, and glutathione reductase. The inhibitory capability of the most effective compounds (IC50 values ranging from 6.44 to 12.6 μM) appears to be associated with a rather significant specificity for ALR2. Molecular mechanics and molecular dynamic calculations performed on the ALR2−inhibitor complex give indications of specific interaction sites responsible for the binding, thus providing information for the design of new inhibitors with improved affinity for the enzyme.

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ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The benzocycloalkenones (I) are coupled with glyoxylic acid (II) in the presence of a base to give the unsaturated acids (III) which are reduced with zinc to form the corresponding saturated compounds (IV).

Cyclocondensation of the dicarboxylic acid (I) with hydrazine hydrate (II) yields the dihydropyridazinone (III) which is converted into the pyridazinone (IV) by bromination/dehydrobromination.

The piperazines (Id) ‐ (Ig), synthesized as outlined in the reaction scheme, are converted to the N‐nitroso derivatives (IX).