Medicinal Chemistry - Volume 4, Issue 5, 2008

Amodiaquine remains one of the most prescribed antimalarial 4-aminoquinoline. To assess the importance of the 4'-hydroxyl group and subsequent hydrogen bond in the antimalarial activity of amodiaquine (AQ), a series of new analogues in which this functionality was replaced by various amino groups was synthesized. The incorporation of a 3'- pyrrolidinamino group instead of the 3'-diethylamino function of AQ allowed the development of a parallel series of amopyroquine derivatives. The compounds were screened against both chloroquine (CQ)-sensitive and -resistant strains of Plasmodium falciparum and their cytotoxicity evaluated upon the MRC5 cell line. Antimalarial activity in a low nanomolar range was recorded showing that the 4'-hydroxy function can be successfully replaced by various amino substituents in terms of activity without any influence of the level of CQ-resistance of the strains. Furthermore the ability of the compounds to inhibit beta-hematin formation was measured in order to discuss the mechanism of action of these new compounds. Compounds 7d and 8d exhibit a high selectivity index and may be considered as promising leads for further development.

The capacity of ten molecules for reversing resistance in Plasmodium falciparum in vitro to quinoline antimalarial drugs, such as chloroquine (CQ), quinine (QN), mefloquine (MQ) and monodesethylamodiaquine (MDAQ), was assessed against 27 Plasmodium falciparum isolates. Four of these compounds were 9,10-dihydroethanoanthracene derivatives (DEAs). These DEAs reversed 75 to 92% of the CQ resistant strains. These synthetic compounds were more effective in combination with CQ than verapamil, ketotifen, chlorpromazine, reserpine or nicardipine, which reversed less than 50% of the CQ resistant strains. DEAs significantly reversed 67 to 100% of MDAQ resistant parasites. These compounds were more effective in combination with MDAQ than ketotifen (60% of reversal), chlorpromazine (45%), verapamil (33%), reserpine (30%) or nicardipine (9%). The reversal activity of MQ resistance was less pronounced, regardless of the molecule tested, and was homogeneous with a rate ranging from 42% for ketotifen to 58% for reserpine, nicardipine, verapamil and cyproheptadine. The four DEAs significantly reversed 50 to 55% of the parasites resistant to MQ. Fifty-six to 78 % of the QN resistant parasites were reversed by the synthetic DEAs. There were few differences in the rate of reversal activity on QN resistant strains between the ten compounds, with rates ranging between 56 to 78% for the ten chemosensitizers. The use of DEAs in combination with quinoline seems to be thus a promising strategy for limiting the development of drug resistant strains and for treating patients in drug resistant areas.

A series of N,N-bis(trifluoromethylquinolin-4-yl)- and N,N-bis[2,8-bis(trifluoromethyl)quinolin-4-yl] diamino alkane and piperazine derivatives were synthesised by employing a simple and rapid displacement reaction of the 4-chloro group on the 2-trifluoromethyl- and 2,8-bis(trifluoromethyl)-quinoline by diaminoalkane or piperazine groups. Results of in vitro antimalarial activity evaluations of these compounds against the chloroquine-sensitive (D10) and chloroquineresistant (K1) strains of Plasmodium falciparum indicate that compounds with trifluoromethyl groups in both the 2 and 8 positions coupled with diaminoalkyl bridging chains of 2 to 6 carbon atoms exhibit a slightly higher activity than compound with only a trifluoromethyl group at position 2, and those with a piperazine bridge These compounds exhibit higher activity in the chloroquine-resistant than in the chloroquine-sensitive strains of the Plasmodium. Comparative studies indicate that the compounds are more selective in their cytotoxicity against the parasite cells. Except for compounds containing a piperazine bridge, this new series of compounds interact with ferriprotoporphyrin IX to more or less the same extent.

Malaria is one of the foremost public health problems in developing countries affecting nearly 40% of the global population. Apart from this, the past two decade's emergence of drug resistance has severely limited the choice of available antimalarial drugs. Furthermore, the general trend emerging from the SAR-studies is that chloroquine resistance does not involve any change to the target of this class of drugs but involves compound specific efflux mechanism. Based on this premise a number of groups have developed short chain analogues of 4-aminoquinoline, which are active against CQ-resistant strains of P. falciparum in in vitro studies. However, these derivatives undergo biotransformation (dealklyation) significantly affecting lipid solubility of the drug. In view of this background information, we thought that it would be interesting to study the effect of additional lipophilicity and cationic charge at the lateral side chain of 4- aminoquinoline. This prompted us to explore the cationic amino acid conjugates namely, lysine and ornithine of 4- aminoquinoline with a view to achieve improved antimalarial activity and to the best of our knowledge such amino acid conjugates have not been hitherto reported in the literature in the case of 4-aminoquinolines. In the present study, a new series of side-chain modified 4-aminoquinolines have been synthesized and found active against both susceptible and multidrug resistant strains of P. falciparum in vitro and P. yoelli in vivo. The seminal finding of the present study is that a new series of compounds having significantly more activity against CQ resistant parasites has been identified.

A series of N10-substituted-2-methyl acridone derivatives are synthesized and are examined for its ability to reverse P-glycoprotein (P-gp) mediated multidrug resistance (MDR) in breast cancer cell lines MCF-7 and MCF-7/Adr. The structural requirement of in-vitro anti-cancer and reversal of drug resistance are studied. The results showed that compound 16 with four carbon spacer exhibited promising in-vitro anti-cancer and reversal of drug resistance in comparison to the other analogues.

A series of novel 1-benzhydryl-sulfonyl-piperazine derivatives 3(a-e) were synthesized by nucleophilic substitution reaction of 1-benzhydryl-piperazine with different sulfonyl chlorides and were characterized by 1H NMR, LC/MS, FTIR and elemental analysis. In the present study, the compounds 3(a-e) exhibited in vivo inhibition of Ehrlich ascites tumor (EAT) cell growth and increased the Median Survival Time (MST) and %ILS of EAT bearing mice. Further treatment of derivatives in vivo resulted in reduction of EAT cell number and ascites formation. The efficacy of the derivatives to inhibit the angiogenesis in vivo was evaluated in tumor bearing mice peritoneum and chorio allantoic membrane (CAM) model. The compounds suppressed the blood vessel formation in vivo in mice peritoneum and in CAM. Among the compounds studied, 3e demonstrated highest tumor inhibitory and anti-angiogenic effects against mouse tumor. However, this phenomenon needs detailed investigation.

Cigarette smoke derived carcinogens have been identified as the main agents implicated in lung carcinogenesis. Epidemiological as well as animal studies have indicated that certain phytochemicals can block the carcinogenic process by enhancing the detoxification of environmental and or dietary carcinogens. Dibenzoylmethane (DBM), a minor constituent of licorice, is a beta-ketone analog of curcumin, a promising chemopreventive agent for colon, breast and skin cancer. The present study was designed to examine the chemopreventive efficacy of DBM in lungs, its global molecular targets and the mechanism of its action. Feeding DBM to A/J mice significantly inhibited benzo[a]pyrene induced DNA adducts in lungs. Further analysis of its global molecular targets in lungs by oligonucleotide microarray revealed expression of several cytoprotective genes including phase II enzymes that are regulated by Nrf2, a basic leucine zipper transcription factor. To decipher if DBM mediates its function via Nrf2 activation, Nrf2 dependent reporter assays were performed. DBM elicited a dose-dependent increase in antioxidant response element (ARE)-driven luciferase reporter activity which correlated with an increase in mRNA expression of NQO1, GSTA2, and GCLC in mouse hepatoma cells, which are well established targets of Nrf2. Conversely, DBM stimulated ARE reporter activity was attenuated by a dominantnegative mutant of Nrf2. Electrophoretic mobility shift assay confirmed that DBM greatly increased the DNA binding activity of Nrf2. In conclusion, DBM mediates the induction of phase II enzymes by Nrf2 activation and inhibits benzo[a]pyrene induced DNA adducts by enhancing its detoxification in lungs.

Thirty four novel 7-fluoro/nitro-1,2-dihydro-5-oxo-8-(sub)-5H-thiazolo[3,2-a]quinoline-4-carboxylic acids were synthesized from 2,4-dichlorobenzoic acid and 2,4-dichloro-5-fluoroacetophenone by multi step reaction, evaluated for in vitro and in vivo antimycobacterial activities against Mycobacterium tuberculosis H37Rv (MTB), multi-drug resistant Mycobacterium tuberculosis (MDR-TB) and Mycobacterium smegmatis (MC2) and also tested for the ability to inhibit the supercoiling activity of DNA gyrase from M. smegmatis. Among the synthesized compounds, 8-[6-[[(1,1- dimethylethoxy)carbonyl]amino]-3-azabicyclo[3.1.0]hex-3-yl]-1,2-dihydro-7-nitro-5-oxo-5H-thiazolo[3,2-a]quinoline-4- carboxylic acid (10q) was found to be the most active compound in vitro with MIC of 0.08 μM and <0.08 μM against MTB and MDR-TB respectively. Compound 10q was found to be 4.5 and >570 times more potent than isoniazid against MTB and MDR-TB respectively. In the in vivo animal model 10q decreased the bacterial load in lung and spleen tissues with 2.51 and 3.71-log10 protections respectively at the dose of 50 mg/kg body weight.

The recent increase in the incidence of tuberculosis with the emergence of multi-drug resistant (MDR) cases has lead to the search for new drugs that are effective against MDR strains of Mycobacterium tuberculosis (M. tb) and can augment the potential of existing drugs against tuberculosis. In the present study a series of naphthalene-1,4-dione derivatives were synthesized and evaluated for their in vitro antimycobacterial activity against M. tb H37Rv strain. Preliminary results indicated that most of the compounds demonstrated significant antimycobacterial activities. The most effective compounds of the series 7, 8 and 10 have MIC values of 3.13 μg/mL and growth inhibition of 99 %. Compound 7 has an IC50 value of 0.49 μg/mL. Compounds 1, 3 and 18 with MIC values of 3.13 μg/mL also showed 96-98 % growth inhibition. The objective of our study is to generate new leads through different mode of action and to optimize their structure to display the potent efficacy.

Helicobacter pylori is now recognized as the primary etiological factor associated with gastritis, peptic ulcer disease and gastric cancers. Fluoroquinolones have been shown to be active against H. pylori. For develop new anti-H. pylori agents, we have investigated the SAR of a series of N-(phenethyl)piperazinyl quinolones for their antimicrobial activity against H. pylori. The anti-H. pylori activity of synthesized compounds along with commercially available anti-H. pylori agents such as metronidazole, and parent quinolones was evaluated by the disc diffusion bioassay. The results indicated that the potency and anti-H. pylori activity profile of the quinolones is highly dependent on the type of substituent at N-1 and the structure of phenethyl unit on piperazine ring. Most compounds containing a cyclopropyl at N-1 exhibited good activity against H. pylori strains. Among them, ciprofloxacin derivative 13 containing 2-methoxyimino-2-(2- chlorophenyl)ethyl moiety was the most active compound.

N3-Substitued thymidine analogues that carry a carboranylalkyl moiety at the N3-position with various spacer lengths have been reported to be good substrates for thymidine kinase (TK1). As part of our continuing effort towards the development of new TK1 substrates for imaging tumor proliferative activity, we have synthesized a series of new N3- substituted analogues of thymidine that carry an aromatic ring with different spacer lengths. The overall yields for 6 and 7 were 13% and 39% in four steps and three steps, respectively, and those for 14, 16 and 18 were in the range of 13%-15% in six steps. The overall yield for 24 was 33% in three steps, and those for 25 and 26 were 64% and 58%, respectively, in one step. Most of these compounds have been tested for TK1 activity by enzymatic assay to identify a good substrate that can be radiolabeled for imaging. The phosphorylation rates of these compounds were 2%-6% compared with that of thymidine. The results from the in vitro enzymatic assays suggest that these N3-substituted thymidine analogues have some potential for imaging TK1 activity if radiolabeled with a suitable isotope.