Potent inhibitors of farnesyltransferase and geranylgeranyltransferase-I

Design, Synthesis and Biological Evaluation of Novel Piperazinone Derivatives as Cytotoxic Agents

Purpose: In this study, a series of piperazin-2-one derivatives were prepared through bioisosteric substitution of the imidazole ring of L-778,123 (imidazole-containing FTase inhibitor) and rearrangement of groups based on the tipifarnib structure. Final compounds were evaluated for their cytotoxic activities on cancer and normal cell lines by MTT assay. Methods: Methyl α-bromophenylacetic acid and 1-(3-chlorophenyl) piperazin-2-one were synthesized using previously described methods. Methyl 2-(4-chlorophenyl)-2-(4-(3- chlorophenyl)-3-oxopiperazin-1-yl) acetate was prepared by reaction between these two compounds in presence of potassium carbonate. Finally, methoxy group of ester was substituted by various amines such as guanidine, thiourea, urea and hydrazide. The synthesized compounds were tested for their cytotoxicity against colon cancer (HT-29) and lung cancer (A549) cell lines as well as MRC-5 (normal fetal lung fibroblasts) cells as a healthy cell line using MTT colorimetric assay method. Results: Replacement of imidazole moiety with guanidine, thiourea, and hydrazide could increase cytotoxicity toward all three cell lines. Some substituents, such as amine, urea, and hydroxylamine exhibited significant cytotoxicity (<500 µM) but lower than L-778,123 as standard compound. Hydroxyl and methoxy substituents did not show significant cytotoxicity. Imidazole substituent group revealed cytotoxicity similar to L-778,123 All compounds showed lower cytotoxic activity against normal cell lines compared with cancer cell lines. Conclusion: It seems the electron density of substituted groups and rearrangement of groups may significantly increase cytotoxic activity.

Molecular Modelling Studies of 1,4-Diaryl-2-Mercaptoimidazole Derivatives for Antimicrobial Potency

Background: :

Imidazoles are considered as potent antimicrobial agents. In view of this 2-mercaptoimidazoles were synthesized and evaluated for antimicrobial study.

Methods::

Some new 2-mercaptoimidazoles 4a-r were synthesized using substituted aniline and substituted phenacyl bromides in the presence of anhydrous sodium carbonate or potassium carbonate and potassium thiocyanate under solvent-free conditions catalyzed by eco-friendly ptoluene sulfonic acid.

Results: :

The structure of compounds was evaluated on the basis of Infrared spectroscopy (IR), 1HNMR (proton nuclear magnetic resonance) and mass spectral studies. These novel compounds were screened for in-vitro antibacterial and antifungal potency against Staphyllococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Candida albicans and Aspergillus niger. Further, the study was rationalized by molecular modeling studies. All the compounds were subjected to molecular modeling studies for inhibition of enzyme 14α-demethylase.

Conclusions::

The compounds were found to be effective in inhibiting the growth of pathogens. The in-silico results depicted that, all the synthesized compounds have minimum binding energy and good affinity towards the active site and thus can be considered as good inhibitors of 14α- demethylase enzyme.

[3H]UR-DEBa176: A 2,4-Diaminopyrimidine-Type Radioligand Enabling Binding Studies at the Human, Mouse, and Rat Histamine H4 Receptors

Differences in sequence homology between human (h), mouse (m), and rat (r) histamine H₄ receptors (H₄R) cause discrepancies regarding affinities, potencies, and/or efficacies of ligands and therefore compromise translational animal models and the applicability of radioligands. Aiming at a radioligand enabling robust and comparative binding studies at the h/m/rH₄Rs, 2,4-diaminopyrimidines were synthesized and pharmacologically investigated. The most notable compounds identified were two (partial) agonists with comparable potencies at the h/m/rH₄Rs: UR-DEBa148 (N-neopentyl-4-(1,4,6,7-tetrahydro-5H-imidazo[4,5-c]pyridin-5-yl)pyrimidin-2-amine bis(2,2,2-trifluoroacetate), 43), the most potent [pEC₅₀ (reporter gene assay) = 9.9/9.6/10.3] compound in the series being slightly G-protein biased and UR-DEBa176 [(R)-4-[3-(dimethylamino)pyrrolidin-1-yl]-N-neopentylpyrimidin-2-amine bis(2,2,2-trifluoroacetate), 46, pEC₅₀ (reporter gene assay) = 8.7/9.0/9.2], a potential "cold" form of a tritiated H₄R ligand. After radiolabeling, binding studies with [³H]UR-DEBa176 ([³H]46) at the h/m/rH₄Rs revealed comparable K_d values (41/17/22 nM), low nonspecific binding (11-17%, ∼K_d), and fast associations/dissociations (25-30 min) and disclosed [³H]UR-DEBa176 as useful molecular tool to determine h/m/rH₄R binding affinities for H₄R ligands.

Design, Synthesis, Antimicrobial Evaluation and Molecular Modeling Study of New 2-mercaptoimidazoles (Series-III)

Background:

A series of novel substituted 2-mercaptoimidazoles was synthesised efficiently and in high yields using one-pot synthesis from m-hydroxyacetophenones.

Methods:

The structures of the newly synthesized compounds were established, their molecular activity was investigated against some bacteria and fungi were further validated using molecular docking study.

Results:

Reaction of o-hydroxyphenacylbromide (2) with substituted aniline and KSCN, in the presence of catalyst p-toluene sulfonic acid afforded 4(a-r) in good yield. The structure of compounds (4a-r) was confirmed by IR, NMR and MS.

Conclusion:

The compounds exhibited excellent antimicrobial potency against the tested microorganism.

Synthesis and Cytotoxicity Evaluation of Some Novel 1-(3-Chlorophenyl)piperazin-2-one Derivatives Bearing Imidazole Bioisosteres

A series of substituted 3-chlorophenylpiperazinone derivatives were synthesised using L-778123 (an imidazole-containing FTase inhibitor) as a model by bioisosteric replacement of the imidazole ring. The final compounds were evaluated against two human cancer cell lines including A549 (lung cancer) and HT-29 (colon cancer) by MTT assay. The results showed that substitution of imidazole ring with 1-amidinourea, semicarbazide, and thiobiuret led to improvement of cytotoxic activity against both cell lines.

Potent and Selective Farnesyl Transferase Inhibitors

We recently described a novel series of CA(1)A(2)X peptidomimetics as farnesyl transferase inhibitors (FTIs). These compounds possess an N-(4-piperidinyl)benzamide scaffold mimicking A(1)A(2) residue. Extensive exploration of structure--activity relationships revealed that replacement of cysteine by substituted benzylimidazoles provided nanomolar FTIs with in vitro activities (18e, IC(50) = 4.60 nM on isolated enzyme, EC(50) = 20.0 nM for growth inhibition on a tumor cell line). The molecular docking of 18e and 19e in the active site of the enzyme provided details of key interactions with the protein and showed that the methionine or phenylalanine residue fits into the aryl binding site.

Macrocyclic piperazinones as potent dual inhibitors of farnesyltransferase and geranylgeranyltransferase-I

A series of macrocyclic piperazinone compounds with dual farnesyltransferase/geranylgeranyltransferase-I inhibitory activity was prepared. These compounds were found to be potent inhibitors of protein prenylation in cell culture. A hypothesis for the binding mode of compound 3o in FPTase is proposed.

Polyamine derivatives as selective RNaseA mimics

Site-selective scission of ribonucleic acids (RNAs) has attracted considerable interest, since RNA is an intermediate in gene expression and the genetic material of many pathogenic viruses. Polyamine-imidazole conjugates for site-selective RNA scission, without free imidazole, were synthesized and tested on yeast phenylalanine transfer RNA. These molecules catalyze RNA hydrolysis non-randomly. Within the polyamine chain, the location of the imidazole residue, the numbers of nitrogen atoms and their relative distances have notable influence on cleavage selectivity. A norspermine derivative reduces the cleavage sites to a unique location, in the anticodon loop of the tRNA, in the absence of complementary sequence. Experimental results are consistent with a cooperative participation of an ammonium group of the polyamine moiety, in addition to it's binding to the negatively charged ribose-phosphate backbone, as proton source, and the imidazole moiety as a base. There is correlation between the location of the magnesium binding sites and the RNA cleavage sites, suggesting that the protonated nitrogens of the polycationic chain compete with some of the magnesium ions for RNA binding. Therefore, the cleavage pattern is specific of the RNA structure. These compounds cleave at physiological pH, representing novel reactive groups for antisense oligonucleotide derivatives or to enhance ribozyme activity.

A cell-based radioligand binding assay for farnesyl: protein transferase inhibitors

Farnesyl:protein transferase (FPTase) catalyzes the covalent addition of the isoprenyl moiety of farnesylpyrophosphate to the C-terminus of the Ras oncoprotein and other cellular proteins. Inhibitors of FPTase (FTIs) have been developed as potential anticancer agents, and several compounds have been evaluated in clinical trials. To facilitate the identification of cell-active FTIs with high potency, the authors developed a method that uses a radiolabeled FTI that serves as a ligand in competitive displacement assays. Using high-affinity [(3)H]-labeled or [(125)I]-labeled FTI radioligands, they show that specific binding to FPTase can be detected in intact cells. Binding of these labeled FTI radioligands can be competed with a variety of structurally diverse FTIs, and the authors show that inhibition of FTI radioligand binding correlates well with inhibition of FPTase substrate prenylation in cells. This method provides a rapid and quantitative means of assessing FTI potency in cells and is useful for guiding the discovery of potent, novel inhibitors of FPTase. Similar methods could be employed in the optimization of inhibitors for other intracellular drug targets.