Pier Vincenzo Plazzi

Synthesis and Structure–Activity Relationships of FAAH Inhibitors: Cyclohexylcarbamic Acid Biphenyl Esters with Chemical Modulation at the Proximal Phenyl Ring

Fatty acid amide hydrolase (FAAH) is a serine hydrolase that catalyzes the intracellular hydrolysis of fatty acid ethanolamides such as anandamide and oleoylethanolamide. Targeting this enzyme may have important therapeutic potentials owing to the multiple physiological roles of these amides. Cyclohexylcarbamic acid biphenyl‐3‐yl ester (URB524) was one of the most promising FAAH inhibitors so far described. We report the modulation of the electronic and steric features of the proximal phenyl ring of this compound by introducing a series of substituents at the ortho and para positions. pIC50 values were found to correlate with molecular features thought to be involved in the recognition step such as steric hindrance and hydrogen‐bonding ability. Derivatives with small polar groups at the para position of the proximal phenyl ring were slightly better FAAH inhibitors than the parent compound URB524.

Synthesis, pharmacological characterization and QSAR studies on 2-substituted indole melatonin receptor ligands

A number of 6-methoxy-1-(2-propionylaminoethyl)indoles, carrying properly selected substituents at the C-2 indole position, were prepared and tested as melatonin receptor ligands. Affinities and intrinsic activities for the human cloned mt1 and MT2 receptors were examined and compared with those of some 2-substituted melatonin derivatives recently described by us. A quantitative structure activity relationship (QSAR) study of the sixteen 2-substituted indole compounds, 5a-k, 1, 8-11, using partial least squares (PLS) and multiple regression analysis (MRA) revealed the existence of an optimal range of lipophilicity for the C2 indole substituent. There are also indications that planar, electron-withdrawing substituents contribute to the affinity by establishing additional interactions with the binding pocket. No mt1/MT2 subtype selectivity was observed, with the relevant exception of the 2-phenethyl derivative 5e, which exhibited the highest selectivity for the h-MT2 receptor among all the compounds tested (MT2/mt1 ratio of ca. 50). Conformational analysis and superposition of 5e to other reported selective MT2 ligands revealed structural and conformational similarities that might account for the MT2/mt1 selectivity of 5e.

5-Benzylidene-hydantoins: synthesis and antiproliferative activity on A549 lung cancer cell line.

Benzylidene hydantoins have been recently reported as a new class of EGFR inhibitors. We describe here a simple and efficient methodology for the parallel solution-phase synthesis of a library of 5-benzylidene hydantoins, which were evaluated for antiproliferative activity on the human lung adenocarcinoma A549 cell line. Various substituents at positions 1, 3 and 5 on the hydantoin nucleus were examined. In the presence of a 5-benzylidene group and of a lipophilic substituent at position 1, most of the tested compounds inhibited cell proliferation at a concentration of 20 microM. Compound 7 (UPR1024), bearing 1-phenethyl and (E)-5-p-OH-benzylidene substituents, was found to be the most active derivative of the series. It inhibited EGFR autophosphorylation and induced DNA damage in A549 cells. Compound 7 and other synthesized 5-benzylidene hydantoin derivatives increased p53 levels, suggesting that the dual mechanism of action was a common feature shared by compound 7 and other member of the series.

Heteroarylaminoethyl and heteroarylthioethyl imidazoles. Synthesis and H3-receptor affinity

Summary -- The synthesis of new H3-receptor antagonists, 4-(2-heteroarylaminoethyl) and 4-(2-heteroarylthioethyl) imidazoles and their H3-receptor affinity obtained from competitive binding curves vs [3H]-NC~-methylhistamine ([3H]NAMHA) on rat brain cortex membranes are described. These compounds are derived from structural modulations of thioperamide and were synthesized in order to study binding interactions with H3-receptors and find alternative lead compounds with H3-receptor antagonist activity. The new compounds differ from thioperamide by the following features: 1) the N-cyclohexylcarbothioamide moiety of thioperamide has been replaced by a benzothiazole (1); 2) the piperidine ring has been replaced by more flexible aminoethyl and thioethyl chains, in order to lower the excessive rigidity of 1 and to test the importance of the tertiary piperidine nitrogen; and 3) the benzothiazole moiety of 1 has been replaced by other heterocyclic nuclei, endowed with different lipophilic, steric and hydrogen-bonding features. Some of the compounds tested showed good affinity for central H3-receptors (pKi range: 5.89-7.96) and can be considered as lead compounds for further optimization studies. The most lipophilic compounds showed higher affinities among benzo-condensed compounds, while imidazolylthioethyl imidazoles were more potent in displacing [3H]NAMHA than thiazolylthioethyl and thiazolylaminoethyl imidazoles which suggests an interaction between the annular NH of the imidazolylthioethyl moiety and the binding site. heteroarylglaminoethylimidazole / heteroarylthioethylimidazole / histamine H3-receptor affinity / [3H]-Na-methylhistamine / rat brain cortex membrane

Indole-based analogs of melatonin: in vitro antioxidant and cytoprotective activities

Abstract:  The known neuroprotective actions of melatonin could be due to its antioxidant or radical scavenging activity, or they could be due to specific interactions of the indole with its receptors. A study of structure–activity relationships may provide useful information when a validated macromolecular target has not been (or is not) identified. A set of indole derivatives, with changes in the 5‐methoxy and acylamino groups, the side chain position and the lipophilic/hydrophilic balance, were selected and tested for their in vitro antioxidant potency in the ABTS (2,2′‐azinobis(3‐ethylbenzothiazoline‐6‐sulfonic acid disodium salt) and thiobarbituric acid reactive substances (TBARS) assays and for their cytoprotective activity against kainate excitotoxicity on cerebellar cell cultures. No quantitative model was able to relate the potencies obtained in the two antioxidant assays, probably because they are related to different physico‐chemical properties. However, the lipophilicity of the compounds and the antioxidant potency in the TBARS assay were linearly correlated. This may be due to improved access to the lipidic substrate, where the antioxidant action occurs. In the cytoprotection assay, most compounds showed potencies comparable with or lower than melatonin. An exception was N‐[2‐(5‐methoxy‐1H‐indol‐2‐yl)ethyl]acetamide (12), yielding, at 50 μm, percentages of cell vitality higher than 75%, while melatonin EC50 was 333 μm. No correlation was observed between cytoprotective and antioxidant potencies, nor with MT1 or MT2 receptor affinity. Compound 12 is a low‐affinity antagonist at melatonin membrane receptors, and one of the most potent compounds in the antioxidant assays; its cytoprotective potency and the absence of agonist activity at melatonin membrane receptors make it a valid candidate for further investigations.

Synthesis and structure-activity relationships of a series of pyrrole cannabinoid receptor agonists

We designed and synthesized a series of pyrrole derivatives with the aim of investigating the structure-activity relationship (SAR) for the binding of non-classical agonists to CB(1) and CB(2) cannabinoid receptors. Superposition of two pyrrole-containing cannabinoid agonists, JWH-007 and JWH-161, allowed us to identify positions 1, 3 and 4 of the pyrrole nucleus as amenable to additional investigation. We prepared the 1-alkyl-2,5-dimethyl-3,4-substituted pyrroles 10a-e, 11a-d, 17, 21, 25 and the tetrahydroindole 15, and evaluated their ability to bind to and activate cannabinoid receptors. Noteworthy in this set of compounds are the 4-bromopyrrole 11a, which has an affinity for CB(1) and CB(2) receptors comparable to that of well-characterized heterocyclic cannabimimetics such as Win-55,212-2; the amide 25, which, although possessing a moderate affinity for cannabinoid receptors, demonstrates that the 3-naphthoyl group, commonly present in indole and pyrrole cannabimimetics, can be substituted by alternative moieties; and compounds 10d, 11d, showing CB(1) partial agonist properties.

Synthesis, antioxidant activity and structure-activity relationships for a new series of 2-(N-acylaminoethyl)indoles with melatonin-like cytoprotective activity.

Abstract:  5‐Methoxy‐2‐(N‐acetylaminoethyl)indole (5d), a melatonin analogue derived from the transposition of the acetylaminoethyl side chain from C3 to C2 of the indole nucleus, had been previously characterized as a low affinity antagonist at MT1 and MT2 membrane receptors; this molecule is endowed with good in vitro antioxidant and cytoprotective potency in rat cerebellar cell cultures, comparable to or better than those of melatonin. In order to further investigate the role of structure–antioxidant activity relationships in cytoprotection, the structure of 5d was systematically modulated to design a new series of compounds. The 5‐methoxy group was replaced by substituents with different electronic and lipophilic properties and it was moved to a different position on the indole ring. Other modifications of the lead structure involved the methylation of the indole nitrogen or its replacement by a sulfur atom. The side chain was also modified either increasing its lipophilicity or introducing an ionisable acid group. The antioxidant activity of this set of compounds was evaluated by the ABTS and conjugated dienes (CD) assays, while their cytoprotection was evaluated against kainate‐induced cytotoxicity in cultured cerebellar neurons. In both antioxidant assays, the shift of the 5‐methoxy group to the 4‐position of the indole nucleus led to the most active radical scavenger (9), more potent than the parent compound and melatonin in the antioxidant tests, but much less effective as a cytoprotectant. Sharp structure–activity relationships were registered for cytoprotection, where the maintenance of the 5‐alkoxy‐2‐(N‐acylaminoethyl)indole scaffold appeared as the key feature to confer both antioxidant and cytoprotective activity to the structure. Some derivatives of the set, however, together with the most potent 5d, maintained a significant antioxidant and cytoprotective effect and could be employed as tools for in vivo pharmacological investigations on neuroprotective efficacy of melatonin‐related indoles.

Antioxidant and cytoprotective activity of indole derivatives related to melatonin.

Melatonin (MLT) is known for its radical scavenger activity, which had been related to its ability to protect neuronal cells from different kinds of oxidative stress. In particular, MLT protects rat cerebellum granular cells from kainate-induced necrosis at concentrations higher than 100 microM, and is able to reduce lipoperoxidation induced by radical stress in rat brain homogenate at similar concentrations. On the other hand, MLT has nanomolar affinity for its membrane receptors (MT1 and MT2), and these are completely saturated at the high concentrations employed when the cytoprotective effect is observed. Other indole derivatives are also known to possess antioxidant and cytoprotective activity. In order to dissociate the cytoprotective effect of MLT from its receptor affinity, and to investigate the structure-activity relationships (SAR) between this effect and some potentially relevant chemical properties, we prepared a series of indole derivatives, where the structure of MLT was gradually modulated, varying the 5-methoxy group nature and position, the acylaminoethyl chain position, and by the introduction of lipophilic groups. These modifications resulted in a set of compounds having different receptor affinity and intrinsic activity, different lipophilicity, and different substitution at the indole nucleus. The compounds were tested for their antioxidant potency by the ABTS test and by inhibition of rat brain homogenate lipoperoxidation; their cytoprotective effect was also estimated from the inhibition of kainate-induced cellular death on rat cerebellum granular cells, and the results were evaluated by SAR comparison and QSAR analysis. An isomer of MLT resulted more potent and effective than MLT itself in the cytoprotection test, although it showed similar potency in the peroxidation test, and it was devoid of the ability to stimulate MT1 and MT2 receptors. This compound was selected as the lead compound for a further SAR study, devoted to the optimization of the cytoprotective effect and to the investigation on its mechanism.

Synthesis and biological assays of new H3-antagonists with imidazole and imidazoline polar groups

New histamine H3-receptor antagonists were synthesised and tested on rat brain membranes and on electrically stimulated guinea-pig ileum. The new compounds have a central polar group represented by a 2-alkylimidazole or a 2-thioimidazoline nucleus. The effect of the polar group basicity on the optimal length of the alkyl chain, connecting this group to a 4(5)-imidazolyl ring, was investigated. The best affinity values, obtained by displacement of [3H]-RAMHA from rat brain, were obtained for the 2-alkylimidazole derivatives (2a-f) with tetramethylene chain (pKi 8.03-8.97), having an intermediate basicity between that of the previously reported 2-thioimidazoles (1a-i) and that of 2-alkylthioimidazolines (3a-h). In contrast, a general lowering of affinity (pKi 5.90-7.63) was observed for compounds of the last series (3a-h), with a complex dependence on the terminal lipophilic group and chain length.

Synthesis and stability in biological media of 1H-imidazole-1-carboxylates of ROS203, an antagonist of the histamine H3 receptor.

A series of carbamate derivatives of the H3 antagonist ROS203 (1) were prepared, and their lipophilicity and steric hindrance were modulated by introducing linear or branched alkyl chains of various lengths. In vitro stability studies were conducted to evaluate how structural modulations affect the intrinsic reactivity of the carbamoyl moiety and its recognition by metabolic enzymes. Linear alkyl carbamates were the most susceptible to enzymatic hydrolysis, with bioconversion rates being higher in rat liver and plasma. Chain ramification significantly enhanced the enzymatic stability of the set, with two derivatives (1g and 1h) being more stable by a factor of 8–40 than the ethyl carbamate 1a. Incubation with bovine serum albumin (BSA) showed a protective role of proteins on chemical and porcine‐liver esterase (PLE)‐catalyzed hydrolysis. Ex vivo binding data after i.v. administration of 1h revealed prolonged displacement of the labeled ligand [3H]‐(R)‐α‐methylhistamine ([3H]RAMHA) from rat‐brain cortical membranes, when compared to 1. However, the high rates of bioconversion in liver, as well as the chemical instability of 1h, suggest that further work is needed to optimize the enzymatic and chemical stability of these compounds.