Synthesis and biological evaluation of potential 5-HT(7) receptor PET radiotracers

Brain serotonin 7 receptor (5-HT₇) is involved in several mood disorders and drug candidates targeting this subtype are currently in development. Positron emission tomography (PET) is a molecular imaging modality offering great promise for accelerating the process from preclinical discovery to clinical phases. As no PET radiopharmaceutical has yet been used successfully to study the 5-HT₇ receptor in vivo, our objective is to develop the first 5-HT₇ fluorine-18 labeled radiotracer.Four structural analogs of SB269970, a specific 5-HT₇ receptor antagonist, divided in FP3 series and FPMP series were synthesized. Their antagonist effects were investigated by cellular functional assay. Nitro-precursors of these analogs were radiolabeled via a [¹⁸F⁻]nucleophilic substitution and in vitro autoradiographies were performed in rat brain.Chemical and radiochemical purities of fluorine radiotracers were >99% with specific activities in 40-129 GBq/μmole range. The four derivates presented antagonism potencies toward 5-HT₇ receptors (pK_B) between 7.8 and 8.8. The four PET radiotracers had suitable characteristic for 5-HT₇ receptor probing in vitro even if the FP3 series seemed to be more specific for this receptor. These results encourage us to pursue in vivo studies.     

Derivatives of 4,6-diamino-1,2-dihydro-2-phenyl-1,2,4-triazolo[4,3-a]quinoxalin-2H-1-one: potential antagonist ligands for imaging the A2A adenosine receptor by positron emission tomography (PET)

The importance of the brain A2A adenosine receptor (A(2A)AR) in movement disorders urges the development of radiolabeled ligands for imaging those receptors by positron emission tomography (PET). This study evaluated one class of A(2A)AR antagonists, derivatives of 4-amino-6-benzylamino-1,2-dihydro-2-phenyl-1,2,4-triazolo[4,3-a]quinoxalin-2H-1-one, 10a, as agents for imaging brain A(2A)ARs by PET.. Modifications of a literature synthesis of 10a efficiently generated analogs 10b-s for pharmacological evaluation. Radioligand binding experiments showed affinities for the rat brain A(2A)AR in the low nanomolar range but similar affinities for the A1AR and substantial unspecific binding. Autoradiography employing [3H]10a, showing that high unspecific binding obscured specific binding to both the A1AR and A(2A)AR. Thus, compounds 10b-s are unsuitable as ligands for imaging brain A(2A)ARs by PET.     

Synthesis and antibacterial activity of some 5-(4-biphenylyl)-7-aryl[3,4-d] [1,2,3]-benzothiadiazoles

A series of 5-(4-biphenylyl)-7-aryl[3,4-d] [1,2,3]-benzothiadiazoles were synthesized, characterized by IR, NMR and elemental analysis and evaluated for in vitro antibacterial activity against some Gram-positive and Gram-negative bacteria. The antibacterial data revealed that compounds 7a-j had better activity against tested Gram-positive organisms than the reference ciprofloxacin and norfloxacin. However, the compounds were nearly inactive against Gram-negative bacteria. Compound 7c and 7d were the most active compounds against Gram-positive bacteria.     

Synthesis of 1-(2-chloro-2-phenylethyl)-6-methylthio-1H-pyrazolo[3,4-d]pyrimidines 4-amino substituted and their biological evaluation

A new series of 4-amino-6-methylthio-1H-pyrazolo[3,4-d]pyrimidines (2a-m) bearing the 2-chloro-2-phenylethyl chain at the N1 position, has been synthesized. The affinity of these compounds for A1 adenosine receptor (A1AR) was measured. The compounds showed poor affinity. A more interesting result was obtained by 2a, 2d, 2g, which demonstrated inhibitory activity on cell proliferation of the A-431 cell line stimulated by epithelial growth factor (EGF) and on EGF receptor tyrosine kinase (EGFR-TK) phosphorylation.     

Synthesis and preliminary evaluation of some N-[5-(2-furanyl)-2-methyl-4-oxo-4H-thieno[2,3-d]pyrimidin-3-yl]-carboxamide and 3-substituted-5-(2-furanyl)-2-methyl-3H-thieno[2,3-d]pyrimidin-4-ones as antimicrobial agents

Two series of N-[5-(2-furanyl)-2-methyl-4-oxo-4H-thieno[2,3-d]pyrimidin-3-yl]-carboxamide (4a-m) and 3-substituted-5-(2-furanyl)-2-methyl-3H-thieno[2,3-d]pyrimidin-4-ones (5a-m) were synthesised using appropriate synthetic route. All the test compounds 4a-m and 5a-m were assayed in vitro for antibacterial activity against two different strains of Gram-negative (Escherichia coli and S. typhi) and Gram-positive (S. aureus, B. subtilis) bacteria and the antimycobacterial activity was evaluated against M. tuberculosis and M. avium strains. The minimum inhibitory concentration (MIC) was determined for test compounds as well as for reference standards. The test compounds have shown significant antibacterial and antimycobacterial activity against all the microbial strains used, when tested in vitro. In general, along with the thienopyrimidinone ring, substituted amido or imino side chain at position 3 is essential for antimicrobial activity. Among the compounds tested, compounds 4c, 4e and 4g in N-[5-(2-furanyl)-2-methyl-4-oxo-4H-thieno[2,3-d]pyrimidin-3-yl]-carboxamide series and compounds 5c, 5e and 5g in 3-substituted-5-(2-furanyl)-2-methyl-3H-thieno[2,3-d]pyrimidin-4-ones series were found to be the most potent. Further the toxicity of most potent compounds 4c, 4e and 4g and 5c, 5e and 5g were assessed using hemolytic assay and minimal hemolytic concentration (MHCs) were determined. In general, test compounds were found to be non-toxic up to a dose level of 200 micromol L(-1) (MHC).     

Synthesis of some novel N4-(naphtha[1,2-d]thiazol-2-yl)semicarbazides as potential anticonvulsants

A series of N(4)-(naphtha[1,2-d]thiazol-2-yl)semicarbazides were designed and synthesized to meet the structural requirements essential for anticonvulsant activity. Anticonvulsant activity was determined after intraperitoneal (i.p.) administration to mice by maximal electroshock (MES) and subcutaneous pentylenetetrazole (scPTZ)-induced seizure tests and minimal motor impairment was determined by rotorod test. A majority of the compounds exhibited significant anticonvulsant activity after intraperitoneal administration. Some of the selected compounds were evaluated orally in rats for activity in scPTZ test at several time points (50 mg/kg). The most active compounds carry bromo, fluoro and nitro substituents at 4-position in the phenyl ring. The biochemical estimations of malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) from brain homogenate not only clearly implicated the role of free radicals in PTZ-induced convulsion but also explained the possible mechanism of protective effect of semicarbazides, through the reduced formation of MDA and increased formation of SOD and GSH-Px.     

Synthesis and biological evaluations of pyrazolo[3,4-d]pyrimidines as cyclin-dependent kinase 2 inhibitors

A series of 1,4,6-trisubstituted pyrazolo[3,4-d]pyrimidines 15-19, 30-38 capable of selectively inhibiting CDK2 activity were synthesized by derivatization at C-4, C-6 and N-1 with various amines and lower alkyl groups. For above synthetic compounds, biological evaluation was carried out and structure-activity relationship was examined. In our series, 4-anilino compounds exhibited better CDK2 inhibitory activity and antitumor activity compared to 4-benzyl compounds. The compounds 33a,b having a 3-fluoroaniline group at C-4 showed comparable or superior CDK2 inhibitory activity to those of olomoucine and roscovitine as reference compounds. In general, the unsubstituted compounds (30a,b, 33a,b, 36a,b) at N-1 possessed higher potency than the substituted compounds (32a,b, 34a,b) for the CDK2 inhibitory activity. As for EGFR inhibitory activity, most compounds didnot have a significant activity. The compounds 32a,b exhibited potent cell growth inhibitory activity against human cancer cell lines, but their CDK2 inhibitory activities were slightly poorer than olomoucine.     

Synthesis, antibacterial and antitubercular activities of some 7-[4-(5-amino-[1,3,4]thiadiazole-2-sulfonyl)-piperazin-1-yl] fluoroquinolonic derivatives

In the present study, a series of 7-[4-(5-amino-1,3,4 thiadiazole-2-sulfonyl)]-1-piperazinyl fluoroquinolonic derivatives VIIa-d were synthesized in good yields and characterized by IR, (1)H-NMR, (13)C-NMR, FAB Mass spectral and elemental analyses. The compounds were evaluated for their preliminary in vitro antibacterial activity against some Gram-positive and Gram-negative bacteria and selected compounds VIIa, b were screened for antitubercular activity against Mycobacterium tuberculosis H(37)Rv strain by broth dilution assay method. The antibacterial data of the tested N-sulfonylfluoroquinolones VIIa-d indicated that all the synthesized compounds showed better activity against Gram-positive bacteria S. aureus, E. faecelis, Bacillus sp. (MIC=1-5 microg ml(-1), respectively) compared to reference drugs. The MIC values of tested derivatives connotes that the sparfloxacin and gatifloxacin derivatives VIIc, d were most active against the tested Gram-positive bacterial strains (MIC=1-5 microg ml(-1)). All the tested compounds VIIa-d showed poor activity against the Gram-negative bacteria. The in vitro antitubercular activity reports of selected compounds VIIa, b against M. tuberculosis strain H(37)Rv showed moderate activity at MIC of 10 microg ml(-1).     

Synthesis of new 2-(5-substituted-3-phenyl-2-pyrazolinyl)-1,3-thiazolino[5,4-b]quinoxaline derivatives and evaluation of their antiamoebic activity

In an effort to develop potent antiamoebic agents, we have synthesized chalcones (1-8), amino-5-substituted-(3-phenyl(2-pyrazolinyl))methane-1-thione derivatives (1a-8a) and 2-(5-substituted-3-phenyl-2-pyrazolinyl)-1,3-thiazolino[5,4-b]quinoxaline derivatives (1b-8b) and evaluated for their in vitro antiamoebic activity against HM1:IMSS strain of E. histolytica. All the compounds were characterized by electronic, IR, (1)H NMR and mass spectroscopic data. It was observed that the antiamoebic activity enhances on modifying the structure of chalcones to the pyrazolines and further to quinoxalines. The MTT assay was performed on human kidney epithelial cell line to check the cytotoxicity of the compounds and the results were compared with metronidazole. Compound 6b showed better antiamoebic activity and less toxicity than metronidazole.     

Synthesis and structural investigation of some pyrimido[5,4-c]quinolin-4(3H)-one derivatives with a long-chain arylpiperazine moiety as potent 5-HT(1A/2A) and 5-HT(7) receptor ligands

A series of new pyrimido[5,4-c]quinolin-4(3H)-ones with variable length of the spacer between amide and 4-arylpiperazine moiety were prepared to further explore the role of a terminal portion in the serotonergic activity. The majority of compounds demonstrated high in vitro affinity for 5-HT_1A receptor, and moderate-to-low affinity for 5-HT_2A and 5-HT₇ receptors. X-ray analysis, two-dimensional NMR, conformational studies and docking into the 5-HT_1A receptor model were conducted to investigate conformational preferences of selected 5-HT_1A receptor ligands in different environments. The extended conformation of tetramethylene derivatives was found in a solid state, in DMSO (for a protonated form) and as a global energy minimum during conformational analysis in simulated water environment. Ligand geometry in top-scored complexes, obtained by docking to a set of 100 receptor models, were either fully extended or with central spacer torsion in synclinal conformation.     

Synthesis of some new bioactive 3-amino-2-mercapto-5,6,7,8-tetrahydro[1]benzothieno[2,3-d]pyrimidin-4(3H)-one derivatives

Nine new 2-(substituted phenyl)/alkyl[1,3,4]thiadiazolo[2,3-b]-6,7,8,9-tetrahydrobenzo(b)thieno[3,2-e]pyrimidin-5(4H)-ones, six new 3-amino-2-[(2-oxo-2-(aryl)ethyl)thio]-5,6,7,8-tetrahydro[1]benzothieno[2,3-d]pyrimidin-4(3H)-ones, one 2-mercapto[1,3,4]thiadiazolo[2,3-b]-6,7,8,9-tetrahydrobenzo(b)thieno[3,2-e]pyrimidin-5(4H)-one and one 2-chloromethyl[1,3,4]thiadiazolo[2,3-b]-6,7,8,9-tetrahydrobenzo(b)thieno[3,2-e]pyrimidin-5(4H)-one were synthesized from 3-amino-2-mercapto-5,6,7,8-tetrahydro[1]benzothieno[2,3-d]pyrimidin-4(3H)-one. The newly synthesized compounds were characterized by analytical and spectral data. Compounds were screened for anti-inflammatory, CNS depressant and antimicrobial activities. Some of the compounds exhibited promising biological activities.     

Synthesis and in vitro antibacterial evaluation of N-[5-(5-nitro-2-thienyl)-1,3,4-thiadiazole-2-yl] piperazinyl quinolones

A series of N-[5-(5-nitro-2-thienyl)-1,3,4-thiadiazole-2-yl]piperazinyl quinolones (7a-c) were synthesized and evaluated for in vitro antibacterial activity against some Gram-positive and Gram-negative bacteria. The antibacterial data revealed that compounds 7a-c had strong and better activity against tested Gram-positive organisms than the reference quinolones such as ciprofloxacin, norfloxacin and enoxacin. However, all three compounds were nearly inactive against Gram-negative bacteria. Compound 7a (ciprofloxacin analogue) was the most active compound against Gram-positive bacteria (MIC=0.008-0.015 mug mL(-1)).     

Synthesis and anti-microbial evaluation of N-[5-(4-tert-amino-2-butynyl)thio-1,3,4-thiadiazol-2yl]-2-phenoxyacetamides

A series of N-[5-(4-tert-amino-2-butynyl)thio-1,3,4-thiadiazol-2-yl]-2-phenoxyacetamides have been prepared. The in vitro anti-microbial activity of these compounds against a variety of Gram-positive, Gram-negative bacteria and Candida species is reported. Some of the prepared derivatives exhibited anti-microbial activity.     

Synthesis of novel 3-amino-2-(4-chloro-2-mercaptobenzenesulfonyl)-guanidine derivatives as potential antitumor agents

Novel 3-amino-2-(4-chloro-2-mercaptobenzenesulfonyl)guanidine derivatives have been synthesized as potential anticancer agents. The in vitro antitumor activity of these compounds has been evaluated in the US National Cancer Institute (NCI), and relationships between structure and antitumor activity are discussed. The prominent compound was 1-allyl-2-[4-chloro-5-(4-chlorophenylcarbamoyl)-2-methylthiobenzenesulfonyl]-3-(5-nitrofurfurylideneamino)guanidine (8) with remarkable activity against 21 human tumor cell lines representing leukemia, lung, colon, melanoma, ovarian, renal, prostate and breast (GI(50)=0.3-3.0microM), and selectivity toward leukemia RPMI-8226 cell line (GI(50)=0.3microM, TGI=1.4microM).     

Asymmetric synthesis and biological evaluation of N-cyclohexyl-4-[1-(2,4-dichlorophenyl)-1-(p-tolyl)methyl]piperazine-1-carboxamide as hCB1 receptor antagonists

We recently discovered and reported a novel series of benzhydrylpiperazine derivatives bearing an asymmetric carbon atom that are potent and selective hCB1 inverse agonists. In the present study, we used Davis-Ellmann-type sulfonamide chemistry to asymmetrically synthesize two enantiomers of the most potent racemic N-cyclohexyl-4-[1-(2,4-dichlorophenyl)-1-(p-tolyl)methyl]piperazine-1-carbo-xamide [14]. Enantiomer separation and configuration assignment were carried out. Our results indicate that the R-configuration is the more active enantiomer, displaying enhanced antagonistic activity for hCB1 receptor, better oral bioavailability, and greater efficacy in the reduction of body weight in diet-induced obese mice.     

Synthesis and antioxidant activity evaluation of new hexahydropyrimido[5,4-c]quinoline-2,5-diones and 2-thioxohexahydropyrimido[5,4-c]quinoline-5-ones obtained by Biginelli reaction in two steps

New hexahydropyrimido[5,4-c]quinoline-2,5-diones and 2-thioxohexahydropyrimido[5,4-c]quinoline-5-ones were prepared in two steps from ethyl 4-phenyl-6-methyl-2-oxo tetrahydropyrimidine-5-carboxylates or 4-phenyl-6-methyl-2-thioxotetrahydropyrimidine-5-carboxylates, previously prepared by Biginelli reaction using appropriate aldehyde, urea derivatives and ethyl acetoacetate. Their antioxidant properties were evaluated by two methods: scavenging effect on 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals and scavenging effect on hydroxyl radicals. The results show that the compounds containing thiourea moiety have better activity.     

Synthesis and antiinflammatory activity of 4-amino-2-aryl-5-cyano-6-{3- and 4-(N-phthalimidophenyl)} pyrimidines

Six new 4-amino-5-cyano-2,6-diarylpyrimidines 5a-h has been synthesized in a facile manner by reacting the appropriate arylamidines 4a-d with bisnitriles 3a-e. Reduction of the nitro group of 5a-e using Pd in ethyl acetate furnished 6a-e in good yields. Reaction of 6a-e individually with phthalic anhydride yielded 7a-e in good to excellent yields. The newly synthesized heterocycles were characterized by IR, (1)H-NMR and mass spectral data. Compounds 5f-h and 7a-e were also evaluated against inflammation. Pyrimidines 5g, h exhibited better antiinflammatory activity when compared with acetylsalicylic acid (ASA). Phthalimide derivatives 7a-e also presented antiinflammatory activity, and three of them, viz., 7a-c have been found to be twice more active than aspirin. Cytotoxical evaluations of compounds 7a-e using neoplastic cells (NCI-H(292) and Hep-2) presented 41% of growth inhibition of neoplastic cells NCI-H(292).