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A novel class of potential MAO-B inhibitors was designed and synthesized in good yield by combining the pyridazinone moiety with the dithiocarbamate framework, two relevant pharmacophores for drug discovery. The biological results obtained for the different pyridazinone/dithiocarbamate hybrids (compounds 8-14) indicated that most of them reversibly and selectively inhibit the hMAO-B in vitro with IC50 values in the µM range and exhibit not significant cellular toxicity. The analogues 9a1, 11a1, 12a2, 12b1 and 12b2, which present the dithiocarbamate fragment derivatized with a piperidin-1-yl or pyrrolidin-1-yl group and placed at C3 or C4 of the diazine ring, were the most attractive compounds of these series. Molecular modeling studies were performed to analyze the binding mode to the enzyme and the structure activity relationships of the titled compounds, as well as to predict their drug-like properties.

The 3-pyridazinylcoumarin scaffold was previously reported as an efficient core for the discovery of reversible and selective inhibitors of MAO-B, a validated drug target for PD therapy which also plays an important role in the AD progress. Looking for its structural optimization, novel compounds of hybrid structure coumarin-pyridazine, differing in polarizability and lipophilicity properties, were synthesized and tested against the two MAO isoforms, MAO-A and MAO-B (compounds 17a-f and 18a-f). All the designed compounds selectively inhibited the MAO-B isoenzyme, exhibiting many of them IC50 values ranging from sub-micromolar to nanomolar grade and lacking neuronal toxicity. The 7-bromo-3-(6-bromopyridazin-3-yl)coumarin (18c), the most potent compound of these series (IC50 = 60 nM), was subjected to further in vivo studies in a reserpine-induced mouse PD model. The obtained results suggest a promising potential for 18c as antiparkinsonian agent. Molecular modeling studies also provided valuable information about the enzyme-drug interactions and the potential pharmacokinetic profile of the novel compounds.

Aim: The current limitations of antiplatelet therapy promote the search for new antithrombotic agents. Here we describe novel platelet aggregation inhibitors that combine pyridazinone and coumarin scaffolds in their structure. Results: The target compounds were synthesized in good yield from maleic anhydride, following a multistep strategy. The in vitro studies demonstrated significant antiplatelet activity in many of these compounds, with IC50 values in the low micromolar range, revealing that the activity was affected by the substitution pattern of the two selected cores. Additional studies point out their effect as inhibitors of glycoprotein (Gp) IIb/IIIa activation. Conclusion: This novel hybrid structure can be considered a good prototype for the development of potent platelet aggregation inhibitors.

The current treatment of Alzheimer’s disease (AD) is mainly focused on enhancing the cholinergic neurotransmission by means of acetylcholinesterase inhibitors (AChEIs). Therefore, there is a growing interest in the development of novel AChEIs. New drugs should not only be able to inhibit the enzyme but also to show optimal parameters of solubility and permeability, since they affect drug bioavailability. Considering the potential advantages of transforming active pharmaceutical ingredients (APIs) into ionic liquids (ILs), five API-ILs derived from two AChEIs, tacrine and a donepezil analogue, were synthesized. The water solubility of these novel API-ILs was analyzed.

Compounds of hybrid structure pyridazine-coumarin were discovered as potent, selective and reversible inhibitors of monoamine oxidase B (MAO-B). These compounds were synthesized in good yield following a multistep approach based on Knoevenagel reaction and using as key intermediate pyridazinone 16, which was obtained from maleic anhydride and furan. Compounds 9b and 9d are the most active compounds of these series, with IC50 values in the sub-micromolar range, and lack of cytotoxic effects. Theoretical calculation of ADME properties also suggested a good pharmacokinetic profile for both compounds. Docking simulations provided insights into enzyme inhibitor interactions and allowed us to rationalize the observed structure-activity relationships (SARs).

Several pyridazin-3(2H)-one derivatives were synthesized starting from alkyl furans using oxidation with singlet oxygen to give 4-methoxy or 4-hydroxybutenolides, key intermediates of the synthetic strategy followed. For all pyridazinones reported, a complete assignment of the 1H and 13C NMR spectra using one- and two-dimensional NMR spectroscopic methods, which included NOE, DEPT, COSY, HSQC and HMBC experiments, was accomplished. Correlations between the chemical shifts of the heterocyclic ring atoms and substituents at N-2 and C-6 were analyzed. Copyright © 2011 John Wiley & Sons, Ltd.

New 6-substituted and 2,6-disubstituted pyridazinone derivatives were obtained starting from easily accessible alkyl furans by using oxidation with singlet oxygen to give 4-methoxy or 4-hydroxybutenolides, key intermediates of this synthetic strategy. The new pyridazinone derivatives have been studied as vasorelaxant and antiplatelet agents. Analysis of biological data revealed the silyl ethers (4a-i) and N,O-dibenzyl derivatives (6g-i) as the most active compounds. © 2010 Elsevier Ltd. All rights reserved.

The purpose of the study was to determine whether novel, selective antagonists of human A 3 adenosine receptors (ARs) derived from the A 3 -selective agonist Cl-IB-MECA lower intraocular pressure (IOP) and act across species. IOP was measured invasively with a micropipette by the Servo-Null Micropipette System (SNMS) and by non-invasive pneumotonometry during topical drug application. Antagonist efficacy was also assayed by measuring inhibition of adenosine-triggered shrinkage of native bovine nonpigmented ciliary epithelial (NPE) cells. Five agonist-based A 3 AR antagonists lowered mouse IOP measured with SNMS tonometry by 3–5 mm Hg within minutes of topical application. Of the five agonist derivatives, LJ 1251 was the only antagonist to lower IOP measured by pneumotonometry. No effect was detected pneumotonometrically over 30 min following application of the other four compounds, consonant with slower, smaller responses previously measured non-invasively following topical application of A 3 AR agonists and the dihydropyridine A 3 AR antagonist MRS 1191. Latanoprost similarly lowered SNMS-measured IOP, but not IOP measured non-invasively over 30 min. Like MRS 1191, agonist-based A 3 AR antagonists applied to native bovine NPE cells inhibited adenosine-triggered shrinkage. In summary, the results indicate that antagonists of human A 3 ARs derived from the potent, selective A 3 agonist Cl-IB-MECA display efficacy in mouse and bovine cells, as well. When intraocular delivery was enhanced by measuring mouse IOP invasively, five derivatives of the A 3 AR agonist Cl-IB-MECA lowered IOP but only one rapidly reduced IOP measured non-invasively after topical application. We conclude that derivatives of the highly-selective A 3 AR agonist Cl-IB-MECA can reduce IOP upon reaching their intraocular target, and that nucleoside-based derivatives are promising A 3 antagonists for study in multiple animal models.

New tetrahydropyran isonucleoside derivatives of purine, with cis or trans configuration, were stereoselectively synthesized in moderate yield by a convergent strategy based on Mitsunobu coupling. The key starting material was a bicyclic lactone.

The synthesis of phosphonate 1,2-disubstituted carbocyclic nucleosides with a cyclopentane ring is described following two different strategies: inclusion of the phosphonomethyl group before or after coupling of the carbocyclic moiety with the heterocyclic base. The diethyl [(trifluoromethanesulfonyl)oxy]methanephosphonate is the key phosphonylating agent for both the strategies.

The oxepane core of zoapatanol was efficiently synthesized from commercially available 1,2,4-butanetriol, and it was shown to be possible to introduce the angular methyl group at C2′ by the reaction of an intermediate butenolide with diazomethane.

A rhodopsin-based homology model of the nucleotide-activated human P2Y2 receptor, including loops, termini, and phospholipids, was optimized with the Monte Carlo multiple minimum conformational search routine. Docked uridine 5'-triphosphate (UTP) formed a nucleobase pi-pi complex with conserved Phe3.32. Selectivity-enhancing 2'-amino-2'-deoxy substitution interacted through pi-hydrogen-bonding with aromatic Phe6.51 and Tyr3.33. A "sequential ligand composition" approach for docking the flexible dinucleotide agonist Up4U demonstrated a shift of conserved cationic Arg3.29 from the UTP gamma position to the delta position of Up4U and Up4 ribose. Synthesized nucleotides were tested as agonists at human P2Y receptors expressed in 1321N1 astrocytoma cells. 2'-Amino and 2-thio modifications were synergized to enhance potency and selectivity; compound 8 (EC50 = 8 nM) was 300-fold P2Y2-selective versus P2Y4. 2'-Amine acetylation reduced potency, and trifluoroacetylation produced intermediate potency. 5-Amino nucleobase substitution did not enhance P2Y2 potency through a predicted hydrophilic interaction possibly because of destabilization of the receptor-favored Northern conformation of ribose. This detailed view of P2Y2 receptor recognition suggests mutations for model validation.

The structure-activity relationships and molecular modeling of the uracil nucleotide activated P2Y6 receptor have been studied. Uridine 5'-diphosphate (UDP) analogues bearing substitutions of the ribose moiety, the uracil ring, and the diphosphate group were synthesized and assayed for activity at the human P2Y6 receptor. The uracil ring was modified at the 4 position, with the synthesis of 4-substituted-thiouridine 5'-diphosphate analogues, as well as at positions 2, 3, and 5. The effect of modifications at the level of the phosphate chain was studied by preparing a cyclic 3',5'-diphosphate analogue, a 3'-diphosphate analogue, and several dinucleotide diphosphates. 5-Iodo-UDP 32 (EC50 = 0.15 microM) was equipotent to UDP, while substitutions of the 2'-hydroxyl (amino, azido) greatly reduce potency. The 2- and 4-thio analogues, 20 and 21, respectively, were also relatively potent in comparison to UDP. However, most other modifications greatly reduced potency. Molecular modeling indicates that the beta-phosphate of 5'-UDP and analogues is essential for the establishment of electrostatic interactions with two of the three conserved cationic residues of the receptor. Among 4-thioether derivatives, a 4-ethylthio analogue 23 displayed an EC50 of 0.28 microM, indicative of favorable interactions predicted for a small 4-alkylthio moiety with the aromatic ring of Y33 in TM1. The activity of analogue 19 in which the ribose was substituted with a 2-oxabicyclohexane ring in a rigid (S)-conformation (P = 126 degrees , 1'-exo) was consistent with molecular modeling. These results provide a better understanding of molecular recognition at the P2Y6 receptor and will be helpful in designing selective and potent P2Y6 receptor ligands.

The synthesis of new 1,2-disubstituted, five- or six-ring-carbocyclic nucleoside analogues of cytidine, compounds 1 and 2a–d, are described. These compounds were obtained by aminolysis, starting from the corresponding uracil derivative, via nucleophilic displacement of a triazolyl (Scheme 1) or a (2,4,6-triisopropylphenyl)sulfonyl (TPS) group (Scheme 2) at 4-position of the pyrimidine ring.

The synthesis of a new series of 1,2-disubstituted carbonucleoside analogues, pyrimidines of general structure I, is reported. These compounds were prepared in good yield from (±)-6-azabicyclo[3.2.0]hept-3-en-7-one (1) via two synthetic routes that involve NaBH 4 -mediated C-N bond cleavage as the key step. The uracil derivative Ia was halogenated with Cl, Br, and I at position 5 by treatment with the corresponding N-halosuccinimide.

A total and versatile synthesis of a new series of carbocyclic nucleoside analogues which are derivatives of purine with a 1,2-disubstituted cyclopentene ring (I) is described. The 6-chloropurine derivatives 3 and 9 were prepared by construction of the heterocyclic base about the primary amino group of the (±)-cis-2-amino-3-cyclopentenylmethanol (1), which was synthesized in good yield from cyclopentadiene in four steps. The substitution of a chlorine atom in the compounds 3 and 9 by an amino group (compounds 4 and 10) and by a hydroxyl group (compounds 5 and 11) was carried out with NH4OH or with NaOH, respectively.

New series of pyridazinone derivatives (4, 5 and 6) were synthesized in good yields following a synthetic strategy based on singlet oxygen oxidation of alkyl furans, in which a suitable β(α)-substituted γ-hydroxybutenolide (10 or 11) or a bicyclic lactone (12 or 13) was the key intermediate. The synthesized compounds were tested in vitro as antiplatelet agents and some of them (compounds 4b, 4d and 5b) exhibited potent inhibitory effects on collagen-induced platelet aggregation with IC50 values in the low μM range. Studies performed with the most active compound of these series (4b) demonstrated its lack of activity as inhibitor of platelet aggregation induced by other agonists as thrombin, ionomycin or U-46619 suggesting a selective action on the biochemical mechanisms triggered by collagen in the platelets.

Phthalazinones are an important kind of nitrogen atom containing heterocyclic compounds due to their synthetic and pharmacological versatility. This fused heterocycle system represents a common structural feature for many bioactive compounds showing a variety of pharmacological activities such as anticancer, anti-diabetic, anti-asthmatic, antihistaminic, antihypertensive, antithrombotic, anti-inflammatory, analgesic, antidepressant or antimicrobial agents, which makes it an attractive scaffold for the design and development of new drugs. This review summarizes detailed and updated information, described in recent non-patent literature, about the most relevant pharmacological properties of phthalazinone derivatives, highlighting the application of this potent pharmacophore in drug discovery.

The pharmacological profile of pyridazinone derivatives includes interesting properties on cardiovascular system as platelet aggregation inhibition and antihypertensive activity. The presence of a 6-aryl group in the pyridazinone ring was considered essential for the activity on cardiovascular system through the inhibition of phosphodiesterase III (PDE III). Recently, the removal / replacement of the aryl group at C6 has provided potent antiplatelet analogues whose activity does not rely on PDE III inhibition. Therefore, in the search of new structural modifications on the pyridazinone ring that could provide derivatives with novel mechanisms of action, we have designed and synthesized pyridazinones with a functionalized alkyl chain at C4, C5 and/or C6 as well as N2 substituted. Vasorelaxant activity was tested on noradrenaline treated intact rat aortic rings showing several derivatives moderate activity. The most promise results were obtained in the platelet aggregation studies performed following the Bo...

We describe an efficient new approach for the synthesis of highly substituted chiral tetrahydrothiophenes, based on the oxidation of a chiral furan substrate with singlet oxygen, followed by intramolecular hetero Michael addition.

In the title compound, C21H24N2O2Si, the carbonyl group of the heterocyclic ring and the O atom of the silyl ether group are placed toward opposite sides and thetert-butyl and pyridazinone moieties areanti-oriented across the Si—O bond [torsion angle = −168.44 (19)°]. In the crystal, molecules are assembled into inversion dimers through co-operative N—H...O hydrogen bonds between the NH groups and O atoms of the pyridazinone rings of neighbouring molecules. The dimers are linked by π–π interactions involving adjacent pyridazinone rings [centroid–centroid distance = 3.8095 (19) Å], generating ladder-like chains along theb-axis direction. The chains are further linked into a two-dimensional network parallel to theabplane through weak C—H...π interactions.

One, two-disubstituted carbonucleoside analogues of purine with unsaturated carbocyclic were synthesized by construction of the heterocyclic base about the primary amino group of the amino alcohol 4 intermediate, which was also synthesized in good yield starting from cyclopentadiene.

Racemic trans-6-chloro-9-[2-(hydroxymethyl)cyclopentyl]purine was resolved using HPLC with a chiral column. The absolute configurations of the enantiomers were determined by NMR studies of their (R)- and (S)-methoxy-phenylacetates.

(1)H and (13)C NMR chemical shifts of cis and trans isonucleoside analogues of purine in which the furanose moiety is substituted by a tetrahydropyran ring were completely assigned using one- and two-dimensional NMR experiments that include NOE, DEPT, COSY and HSQC. The significant (1)H and (13)C NMR signals differentiating between the cis and trans stereoisomers were compared.

The phosphate, uracil, and ribose moieties of uracil nucleotides were varied structurally for evaluation of agonist activity at the human P2Y(2), P2Y(4), and P2Y(6) receptors. The 2-thio modification, found previously to enhance P2Y(2) receptor potency, could be combined with other favorable modifications to produce novel molecules that exhibit high potencies and receptor selectivities. Phosphonomethylene bridges introduced for stability in analogues of UDP, UTP, and uracil dinucleotides markedly reduced potency. Truncation of dinucleotide agonists of the P2Y(2) receptor, in the form of Up(4)-sugars, indicated that a terminal uracil ring is not essential for moderate potency at this receptor and that specific SAR patterns are observed at this distal end of the molecule. Key compounds reported in this study include 9, alpha,beta-methylene-UDP, a P2Y(6) receptor agonist; 30, Up(4)-phenyl ester and 34, Up(4)-[1]glucose, selective P2Y(2) receptor agonists; dihalomethylene phosphonate analogues 16 and 41, selective P2Y(2) receptor agonists; 43, the 2-thio analogue of INS37217 (P(1)-(uridine-5')-P(4)-(2'-deoxycytidine-5')tetraphosphate), a potent and selective P2Y(2) receptor agonist.

Activation of the G(q)-coupled P2Y(6) receptor heterologously expressed in astrocytes significantly attenuates apoptosis induced by tumor necrosis factor alpha (TNFalpha). We have extended the analysis of P2Y(6) receptor-induced cytoprotection to mouse skeletal muscle cells endogenously expressing this receptor. The endogenous P2Y(6) receptor agonist UDP and synthetic agonist MRS2693 protected C2C12 skeletal muscle cells against apoptosis in a concentration-dependent manner (0.1-10 nM) as determined by propidium iodide staining, histochemical analysis using hematoxylin and Hoechst 33258, and DNA fragmentation. The insurmountable P2Y(6) receptor antagonist MRS2578 blocked the protection. TNFalpha-induced apoptosis in C2C12 cells correlated with activation of the transcription factor NF-kappaB. The NF-kappaB activation was attenuated by 10nM MRS2693, which activated the antiapoptic ERK1/2 pathway. In an in vivo mouse hindlimb model, MRS2693 protected against skeletal muscle ischemia/reperfusion injury. The P2Y(6) receptor is a novel cytoprotective receptor that deserves further exploration in ameliorating skeletal muscle injury.

We have prepared a caged form (MRS2703) of a potent dual agonist of the P2Y(1) and P2Y(12) nucleotide receptors, 2-MeSADP, by blocking the beta-phosphate group with a 1-(3,4-dimethyloxyphenyl)eth-1-yl phosphoester. Although MRS2703 is itself inactive at human P2Y(1) and P2Y(12) receptors expressed heterologously in 1321N1 astrocytoma cells or in washed human platelets, this derivative readily regenerates the parent agonist upon mild irradiation with long-wave UV light (360 nm). The functional effect of the regenerated agonist was demonstrated by a rise in intracellular calcium mediated by either P2Y(1) or P2Y(12) receptors in transfected cells. Washed human platelets exposed to a solution of MRS2703 were induced to aggregate upon UV irradiation. At 1.0 microM MRS2703, full aggregation was achieved within 1 min of irradiation. Thus, this caged nucleotide promises to be a useful probe for potent P2Y receptor activation with light-directed spatial and temporal control.

The preparation of new analogues of 5-alkynyl- and 5-alkenyl-uracil is described. The synthesis involved palladium-catalyzed C-C coupling reactions, with the 5-ethynyl, 5-(1-hexynyl), and 5-(2-phenylethynyl) derivatives prepared through a Sonogashira coupling. A Stille coupling reaction was used to obtain the 5-(1-hexynyl) derivative, whilst the (E)-5-(2-bromovinyl) derivative was prepared using the Heck reaction. All the methods were clean and simple to perform.

Diketopiperazines (DKPs) are a common motif in various biologically active natural products, and hence they may be useful scaffolds for the rational design of receptor probes and therapeutic agents. We constructed a new bicyclic scaffold that combines a DKP bridged with a 10-membered ring. In this way we obtained a three-dimensional molecular skeleton, with several amendable sites that provide a starting point to design a new combinatorial library having diverse substituent groups. Structural variation is based upon the flexibility of alkylation of the nitrogen atoms of the DKP and on the side-chain olefin. We obtained a 10-membered secondary ring through a ring-closure metathesis reaction using the second generation Grubbs catalyst. Rings containing both O-ethers and S-ethers were compared. N-Alkyl or arylalkyl groups were introduced optionally at the two Nalpha-atoms. This is a general scheme that will allow us to test rings of varying sizes, linkages, and stereochemical parameters. The DKP derivatives were tested for activity in astrocytoma cells expressing receptors coupled to phospholipase C. Inhibitory effects were observed for signaling elicited by activation of human nucleotide P2Y receptors but not m3 muscarinic receptors. Compound 20 selectively inhibited calcium mobilization (IC50 value of 486 +/- 16 nM) and phosphoinositide turnover elicited by a selective P2Y1 receptor agonist, but this compound did not compete for binding of a radiolabeled nucleotide-competitive receptor antagonist. Therefore, the new class of DKP derivatives shows utility as pharmacological tools for P2Y receptors.

The title N-benzylphthalimide derivative, C16H13NO3, consists of two planar moieties, viz. the phthalimide system (r.m.s. deviation = 0.007 Å) and the phenyl ring, which make a dihedral angle of 84.7 (6)°. The methoxy group is almost coplanar with the phathalimide ring, as shown by the C—C—O—C torsion angle of −171.5 (2)°. In the crystal, the molecules are self-assembled via non-classical C—H...O hydrogen bonds, forming a tape motif along [110].

Activation of the P2Y(1) nucleotide receptor in platelets by ADP causes changes in shape and aggregation, mediated by activation of phospholipase C (PLC). Recently, MRS2500(2-iodo-N(6)-methyl-(N)-methanocarba-2'-deoxyadenosine-3',5'-bisphosphate) was introduced as a highly potent and selective antagonist for this receptor. We have studied the actions of MRS2500 in human platelets and compared these effects with the effects of two acyclic nucleotide analogues, a bisphosphate MRS2298 and a bisphosphonate derivative MRS2496, which act as P2Y(1) receptor antagonists, although less potently than MRS2500. Improved synthetic methods for MRS2500 and MRS2496 were devised. The bisphosphonate is predicted to be more stable in general in biological systems than phosphate antagonists due to the non-hydrolyzable CP bond. MRS2500 inhibited the ADP-induced aggregation of human platelets with an IC(50) value of 0.95 nM. MRS2298 and MRS2496 also both inhibited the ADP-induced aggregation of human platelets with IC(50) values of 62.8 nM and 1.5 microM, respectively. A similar order of potency was observed for the three antagonists in binding to the recombinant human P2Y(1) receptor and in inhibition of ADP-induced shape change and ADP-induced rise in intracellular Ca(2+). No substantial antagonism of the pathway linked to the inhibition of cyclic AMP was observed for the nucleotide derivatives, indicating no interaction of these three P2Y(1) receptor antagonists with the proaggregatory P2Y(12) receptor, which is also activated by ADP. Thus, all three of the bisphosphate derivatives are highly selective antagonists of the platelet P2Y(1) receptor, and MRS2500 is the most potent such antagonist yet reported.

Racemic trans-6-chloro-9-[2-(hydroxymethyl)cyclopentyl]purine was resolved using HPLC with a chiral column. The absolute configurations of the enantiomers were determined by NMR studies of their (R)- and (S)-methoxy-phenylacetates.

One, two-disubstituted carbonucleoside analogues of purine with unsaturated carbocyclic were synthesized by construction of the heterocyclic base about the primary amino group of the amino alcohol 4 intermediate, which was also synthesized in good yield starting from cyclopentadiene.