Medicinal Chemistry - Volume 4, Issue 2, 2008

From the carbolithiation of 6-morpholino fulvene (3) and different lithiated nitrogen containing heterocycles (2-N-methylimidazolyl, 2-N-(N,N-dimethylamino)methyl-imidazolyl, and 2-N-methylindolyl), the corresponding lithium cyclopentadienide intermediate (4a-c) was formed. These three lithiated intermediates underwent a transmetallation reaction with TiCl4 resulting in morpholino-functionalised titanocenes 5a-c. When these titanocenes were tested against LLC-PK cells, the IC50 values obtained were of 24, 36, and 41 μM respectively. The most cytotoxic titanocene in this paper (5a) with an IC50 value of 24 μM is found to be almost ten times less cytotoxic than cis-platin, which showed an IC50 value of 3.3 μM when tested on the epithelial pig kidney LLC-PK cell line, and approximately 2 times less cytotoxic than its dimethylamino-functionalised analogue. Encouragingly however, the IC50 value obtained for titanocene 5a is approximately 100 times better than titanocene dichloride itself.

In vivo and in vitro assays were performed with S91 murine melanoma cells aiming to investigate the effects of testosterone and photoperiod on tumor growth and melanogenesis (tyrosinase activity). In vivo assays were performed by inducing melanoma tumors in castrated mice receiving increasing concentrations of testosterone and submitted to varying photoperiod regimens. The results demonstrated that the increase of melanin content was higher in animals submitted to the longest days, thus demonstrating the importance of photoperiod length in melanin synthesis. Increase in tumor growth and protein content was observed in testosterone-treated animals submitted to 12L:12D; in testosterone-treated animals submitted to 4L:20D and 20L:4D tumor growth was significantly smaller. In S91 cultured cells, testosterone increased cell proliferation and reduced tyrosinase activity in a dose-dependent manner. Radioactive binding assays demonstrated that the hormone was acting through low affinity testosterone receptors, since the presence of aromatase inhibitor did not affect the binding assay in a statistically significant way, and all the in vitro experiments were performed in the presence of the inhibitor. Our in vivo data added to the in vitro results corroborate the hypothesis that S91 melanoma cells directly respond to testosterone and that this effect is modulated by light.

Marine invertebrates provide a series of natural products with different biological activities. Several of these compounds and their derivatives showed a potent anticancer effect. Tunicates represent an important source of bioactive agents, leading to the isolation of ecteinascidin-743 (ET-743), a compound isolated from the Caribbean sea squirt Ecteinascidia turbinata with a potent cytotoxic activity against a variety of tumours in vitro and in vivo. Current phase II clinical trials against soft tissue sarcomas in Europe and the United States indicate that ET-743 represents a highly promising anticancer agent. Another example is aplidine from the Mediterranean tunicate Aplidium albicans, with a broad spectrum activity against various types of cancers, such as colorectal, lymphoma, thyroid and renal cancers. In the present work, we reported, for the first time, that a partially purified methanolic extract prepared from the ascidian Ciona intestinalis inhibited cell proliferation in human cell lines of different origin, including Caco2, HPB-ALL, U-937 and HL-60 and induced early apoptotic events, such as caspase-3 activation and internucleosomal DNA degradation. We suggest the presence in the Ciona intestinalis extract of bioactive compounds possessing anticancer activity.

Quantitative structure activity relationship (QSAR) studies of selective COX-2 inhibitors of commercial interest (drugs in market and on clinical trials) were performed. The COX-2 inhibitory activity (pIC50=-logIC50) of these twelve compounds was correlated with nineteen descriptors including steric, electronic and constitutional parameters. pIC50 activity showed high positive correlation with both volume and HOMO (Highest occupied molecular orbital). A Biparametric model was developed that included both these descriptors. The predictive capability (q2= 0.66) of this equation was satisfactory. So it can be used to design newer templates or modify existing templates. Volume is an important parameter for the selective COX-2 inhibitory activity, because the secondary pocket in the active site of this enzyme is bigger than the active site of COX-1 enzyme (by 17%). HOMO is a measure of the nucleophilicity of the molecule and a molecule with high HOMO energy is ready to donate its electrons and thus is more reactive than molecule with low values. Binding studies were performed between the COX-2 enzyme and these molecules. The inhibitory activity increased with decrease in binding energy (or interaction energy) between the compounds with the COX-2 enzyme (with a correlation coefficient = -0.65). Calculated Log BBB (Blood Brain barrier), Log P (octonol water partition) and HBD (hydrogen bond donor) values were in the acceptable range (i.e., BBB = -1 to 0.3; LogP= 0 to 5; HBD < 5).

The proprotein convertases (PCs) are serine proteases involved in various physiological processes and their overactivity or inactivity has been linked to different disorders. PCs are responsible for the proteolytic processing of various polypeptide precursors. Here, we discuss the effect of their N-terminal prosegments on various PC substrates processing and functions.

Novel 2-carbonyl analogues of diphenidol (1) - bearing lipophylic 1-substituents (2) - were synthesized starting from previously investigated diphenidol derivatives acting as M2-selective muscarinic antagonists. These compounds were tested for receptor binding affinity versus human muscarinic M1-M5 receptors stably expressed in CHO-K1 cells. Their activity in functional assays carried out on CHO-K1 cells expressing human M4 receptors (CHO-hM4) and on classical models of M1-M3 receptors, in guinea pig and rabbit tissue preparations, was also evaluated. Compound 2d showed an affinity of pKi = 7.73 at the human M4-receptor subtype with selectivity ratios ranging from 31-fold (M4/M5) to 60-fold (M4/M2). Interestingly this compound, in CHO-hM4 cells, blocked the inhibition of forskolin-activated cAMP accumulation produced by carbachol (IC50= 61 nM) whereas it was a weak muscarinic antagonist in functional tests carried out in guinea-pig and rabbit tissue expressing M1 (pKb = 5.96), M2 (pKb = 6.43) and M3 (pKb = 6.09) receptors. In conclusion, the modifications performed in this work on reference compounds led us to obtain surprisingly a M4 selective antagonist. Considering the therapeutic indications for M4 selective antagonists, compound 2d may serve as a novel lead compound for further optimization.

The 21-amino acid peptide endothelin-1 (ET-1) is the predominant isoform of the endothelin peptide family, which includes ET-2, and ET-3. These peptides display a variety of physiological activities including vasoconstriction and the stimulation of cell proliferation in tissues both within and outside of the cardiovascular system. They exert their actions via activation of two distinct receptor subtypes, ETA and ETB, belonging to the G protein-coupled receptor (GPCR) superfamily. Ligands of these receptors have received numerous citations in the recent pharmaceutical literature. In particular receptor antagonists, both ETA- and ETB-selective, as well as non-selective, have been described due to their wide therapeutic potential. As a part of our program toward the development of selective ETA ligands we have designed and we now report new molecules based on 2-substituted-4-aryl-3-quinolinecarboxylic acid moiety. Binding profile for some compounds (40, 44, 46, and 47) of this class showed a reasonable affinity and selectivity for ETA receptors.

We have carried out the study of the photochemical properties of a series of synthetic mesotetraphenylsulfonated porphyrins (TPPMS4) bonded to several metal ions such as: Cu(II), Zn(II), Pd(II), Mn(II), Fe(III), Ni(II) and Co(II) for the optimization of their clinical applications as antiviral agents against the human immunodeficiency virus (HIV-1) as well as the study of the in vitro antiviral photoinactivation mechanisms with future application in blood sterilization. A selective inhibition has been determined in the viral growth (HIV-1) when this is irradiated in the presence of the complex TPPFeS4 and TPPMnS4 (photosensitizer-mediated Type I reaction) as well as in the 1O2- mediated (Type II reaction) in the presence of TPPPdS4 and TPPZnS4, remaining cellular viability unaltered in each case.

A series of thiophene derivatives 1a-d & 2a-c were synthesized by condensation of 5-nitro-2-thiophene carboxaldehyde with mono and diamines respectively. Various imidazole derivatives 3a-c were obtained by condensing 4-(2- ethylamino)-1H-imidazole with 4-acetylpyridine, 2-acetylpyridine and 4-acetylbenzonitrile respectively. Pyridine derivatives 4a-e were synthesized by condensing 2-hydrazino-pyridine with various carbonyl compounds; 5a-c by condensing 2, 6-pyridine dicarbonyl dichloride with various aryl sulfonylhydrazides; 6, 7 by condensing 2, 6-dialdehyde pyridine with 2-hydrazinopyridine and anthranilonitrile respectively and compound 8 by condensing 2, 5-thiophene dialdehyde with hydrazinopyridine. All the compounds were characterized by IR, 1HNMR, Mass spectra and elemental analysis. Compounds 1a-d; 2a-c; 3a-c; 4a-e; 5a-c, 6, 7 and 8 were screened for anti-inflammatory and analgesic activities. Compounds 1b and 2c exhibited good anti-inflammatory (26.5% and 33.4% at 50mg/kg p.o. respectively) and 3a, 3c good analgesic (100% and 75% at 100 mg/kg p.o. respectively) activities.

Translesion synthesis (TLS) is one of the DNA damage tolerance strategies that has evolved to enable organisms to replicate their genome despite the presence of unrepaired damage. TLS complexes are dynamic systems composed of DNA polymerases and associated protein factors. Therefore, it is hard to study these assembles by X-ray analysis or other instrumental methods. Here, we have suggested applying the photoaffinity labeling technique for studying the TLS system in nuclear/cellular extracts. As a tool we proposed to use partial DNA duplexes containing base-substituted photoreactive deoxynucleotides at the 3'-end of primer opposite to DNA damage at the template strand. We demonstrated that photoreactive dNTPs can be potentially used to synthesize photoreactive DNA probes mimicking the DNA intermediates of the first stage of translesion synthesis by specialized DNA polymerases. We used synthetic apurinic/apyrimidinic site (AP-site) - tetrahydrofuran (THF) and 8-oxoguanine as damages in +1 position of the template strand with respect to 3'-end of primer. Activity of human DNA polymerases β and λ was exploited for construction of photoreactive DNAs using photo derivatives of dNTPs. The kinetic parameters of the elongation reaction in model systems were estimated. Using photoaffinity crosslinking we found that only a few proteins in the bovine testis nuclear extract were strongly labeled by TLS probes.

Twenty-five 3-substituted isocoumarins were synthesized using cutting edge microwave-assisted technology in high yields. The syntheses of different isocoumarins were carried out in a single step by the direct condensation of homophthalic acid with aryol and acyl chlorides under the solvent-free conditions without any solid support. The structures of all the synthesized compounds were characterized using different spectroscopic techniques including UV, IR, 1HNMR and EIMS and purity was confirmed by CHN analysis. All the synthesized compounds were tested for in vitro leishmanicidal activity. Compounds 3a, 3b, 3g, 3l, 3m, 3r, 3t, 3w, 3x, and 3y displayed potential in vitro leishmanicidal activity with IC50 values in the range of 0.56-84.38 μg/ml, whereas standard inhibitors amphotericine B have IC50 = 0.24 μg/ml. The compounds 3b, 3g, 3m, 3t, 3w, 3x, and 3y having IC50 values 27.86, 28.88, 36.49, 34.37, 28.68, 0.89 and 0.56 μg/ml, respectively, were most active among the present series while remaining others were found less active. The compound 3x and 3y can act as potential lead molecules for further development of isocoumarin-based new drugs for the treatment of leishmaniasis.

The methodology for predicting the distribution of compounds between Blood and Brain, i.e. their brain/blood partition coefficients (logBB values), was studied using a nonlinear regression analysis in this work. The equations were established on the basis of the different states (neutral, cationic and anionic) of the compounds distributing into the three dominating composition (lipid, protein and water) of the brain. The equations bear strong fitting and predictive power for the distribution of compounds (total set: n=160, r=0.906, s=0.326; training set: n=139, r=0.908, s=0.320; testing set: n=21, r=0.903, s=0.297), and can describe the distribution of the different states of the compounds in three compositions of brain. The compounds in the dataset contained many different types, such as drug molecules, small structure-simple molecules, carboxylic acids and also alkaloids. Therefore the equations were very useful and instructional for the prediction of the compound distribution into the brain and blood. Finally, the percentages of the amount of a compound in lipid, protein and water in brain were calculated using the model, such subdivision will be very useful in drug research and discovery. By an analysis of the percentages a conclusion can be obtained that a well distributed drug is mainly affected by distribution of lipid and protein.

The title compounds have been synthesized and tested for structure activity relationship for Phospholipase A2 (PLA2) [E.C. 3.1.1.4] enzyme inhibition. The in vitro anti-tubercular, PLA2 enzyme inhibitory activities of azetidin-2-one derivatives and in vivo anti-inflammatory studies using mice are highlighted. The analogues of azetidin-2-one were prepared based on the initial activity against Mycobacterium tuberculosis (Mtb). Certain azetidin-2-one analogues described herein showed moderate to good anti-tubercular activity. In particular, two compounds (4f) and (4g) exhibited MIC values of 1.56 and 0.78 μg/mL respectively against the Mtb H37Rv strain. Chloro substitution on aryloxy acid apparently enhanced the antimycobacterial activity and also PLA2 inhibition in the azetidin-2-one series described herein. The ability of azetidin-2-one analogues as anti-inflammatory agents has also been determined. The results show some correlation between anti-inflammatory, anti-tubercular activity and expression of PLA2 enzyme.