Increase of leishmanicidal and tubercular activities using steroids linked to aminoquinoline
- Luciana MR Antinarelli†1,
- Arturene ML Carmo†2,
- Fernando R Pavan3,
- Clarice Queico F Leite3,
- Adilson D Da Silva2Email author,
- Elaine S Coimbra1 and
- Deepak B Salunke4
© Bai et al.; licensee Springer. 2012
Received: 16 September 2011
Accepted: 15 January 2012
Published: 2 May 2012
Aminoquinoline/steroid conjugates were synthesized based on the fact that steroid transporters have been shown to accept and carry a variety of drugs. So, in continuing our research of antileishmanial and antitubercular drugs, aminoquinoline/steroid conjugates (12, 13, and 14) were regioselectively synthesized via 1, 3-dipolar cycloaddition of alkynes 3, 5, and 7 with azide 12. The aminoquinoline/steroids conjugates were evaluated in vitro against Leishmania major and Mycobacterium tuberculosis.
Regioselective synthesis of the novel aminoquinoline/steroid conjugates was achieved in very high yield. All aminoquinoline/steroid conjugates (12, 13, and 14) exhibited best results against Leishmania and M. tuberculosis than the respective alkyne intermediate structures (3, 5, and 7, respectively). Among them, the compound 12 exhibited the best activity for M. tuberculosis (MIC = 8.8 μM). This result is comparable to drugs commonly used in tuberculosis treatment. Also, for antileishmanial assay, the aminoquinoline/steroid conjugates demonstrated a significant activity against promastigote and amastigote forms of L. major.
Addition of a steroid group to aminoquinoline molecules enhanced the leishmanicidal and antitubercular activities. These results highlight the importance of steroids as carrier.
KeywordsAntileishmanial drugs Antituberculosis drugs Click chemistry Quinoline Steroid
Quinolines are among the most important antimalarial drugs ever used [1, 2]. In addition, quinoline derivatives have also demonstrated a variety of biological properties that includes antiviral, anti-inflammatory, antitubercular, and antileishmanial activities [2–5]. Leishmaniasis is a disease caused by parasitic protozoans of the genus Leishmania. Over 20 different Leishmania species can infect humans and cause a wide spectrum of symptoms. It has an estimated prevalence of 12 million cases worldwide, which is continuing to increase, with 1.5–2 million new cases each year . With no available vaccine, the chemotherapy is a major control for the disease. However, the treatment options are severely limited and first line treatment is based on pentavalent antimonials that have been used in therapeutics for more than half a century . Tuberculosis (TB) is another important neglected disease. TB is more prevalent in the world today than at any other time in human history. Mycobacterium tuberculosis (MTB), the pathogen responsible for TB, uses diverse strategies to survive in a variety of host lesions and to evade immune surveillance [7, 8]. The last 20 years have seen the worldwide appearance of multidrug-resistant TB, followed by extensively drug-resistant TB, and most recently, strains that are resistant to all antituberculosis drugs . Since the discovery of rifampicin (1960), no new drugs have been developed specifically against mycobacteria . Also, only within the last few years some promising drug candidates have emerged . Considering the inefficacy and the high toxicity of the currently used drugs for the treatment of these infectious diseases, as well as the emergence of drug-resistant strains of the causative organisms, the development of new leishmanicidal and antitubercular agents is extremely important.
Bioconjugation has emerged as a fast growing technology and aims at the ligation of two or more molecules to form new complexes with the combined properties of their individual components . To make this linkage, the 1,2,3-triazole moieties are attractive as connecting units, since they are stable to metabolic degradation and capable of hydrogen bonding, which can be favorable in binding to biomolecular targets and also improves solubility . Although the 1,2,3-triazole structural moiety does not occur in nature, the synthetic molecules containing the 1,2,3-triazole unit show diverse biological activities including antibacterial, herbicidal, fungicidal, anti-allergic, and anti-HIV . Aminoquinoline/cholic acid conjugates were synthesized based on the fact that steroid transporters have been shown to accept and carry a variety of drugs . Cholic acid is the most common form of the steroid and its derivatives are known to exhibit antimicrobial activities . Bile acids are amphiphilic molecules which may represent alternatives for chemotherapeutic agents by acting synergistically with antibiotics as membrane permeabilizers [17–21]. Moreover, several bile acid/drug conjugates are shown to possess better activity than the precursor [22, 23].
In a previous study, we demonstrate that 4-amino-7-chloroquinoline derivatives showed an interesting antileishmanial and anti-MTB activities . In continuation of this study were synthesized aminoquinoline conjugate with steroids in the expectation of improving its biological activity.
General experimental techniques and apparatus
TLC was performed on precoated silica gel F254 plates (0.25 mm; E. Merck). Infrared spectra were recorded on Schimadzu 8400 series FTIR instrument. 1 H NMR spectra were recorded on a Bruker AC-300 and 500 spectrometers at 300.13 and 500.13 MHz and 13C NMR spectra were recorded on a Bruker AC-300 at 75 MHz. The chemical shifts are given in parts per million relative to tetramethylsilane. Mass spectra were recorded on LC–MS/MS-TOF API QSTAR PULSAR spectrometer, and samples were introduced by infusion method using Electro spray Ionization Technique. Standard work up: after extraction of all the reactions, the organic extracts were washed with water and brine and dried over anhydrous Na2SO4 and concentrated in vacuum.
Synthesis of terminal acetylenes
General synthetic procedure for N-(7-chloroquinolin-4-yl)alkyl-diamine) (2, 4, and 6)
A mixture of 4,7-dichloroquinoline (2.0 g, 10.1 mmol) and the corresponding diamines (50.0 mmol), ethane-1,2-diamine, propane-1,3-diamine, or buthane-1,4-diamine, was heated at 80°C for 1 h without stirring for 1 h and then at 110°C for 4–6 h with continued stirring to drive the reaction to completion. The reaction mixture was cooled to room temperature and diluted with dichloromethane. The organic layer was successively washed with 5% NaOH (30 mL) followed by water wash and then finally with brine. The organic layer was dried over anhydrous Na2SO4 and solvent was removed under reduced pressure to afford the compounds 2, 4, and 6, at 80–90% yield.
N-(7-chloroquinolin-4-yl)ethane-1,2-diamine ( 2 ) : Yellow solid, yield: 90%; mp = 141°C (145-147°C).
N-(7-chloroquinolin-4-yl)buthane-1,4-diamine ( 6 ) : Yellow solid, yield: 80%; mp = 123°C (122–124°C).
General synthetic procedure for 7-chloro-N-(3-(prop-2-ynylamino)alquil)quinolin-4-amine (3, 5, and 7)
The compounds 2, 4, and 6 (6.8 mmol) and propargyl bromide (13.6 mmol), in presence of K2CO3 (13.6 mmol), were dissolved in EtOH (5.0 mL). The reaction mixture was stirred at 0°C for 2 h and then at 25°C for 48 h. Solvent was removed in vacuum until dry. The crude reaction product was purified by flash chromatography (eluent: MeOH/CH2Cl2 5:95) producing the compounds 3, 5, and 7, respectively (2.5 mmol) in 60% yield as yellow solid.
7-chloro-N-(2-(prop-2-ynylamino)ethyl)quinolin-4-amine ( 3 ) : Yield: 60%, mp = 99°C.
7-chloro-N-(3-(prop-2-ynylamino)propyl)quinolin-4-amine ( 5 ) : Yield: 60%, mp = 75°C.
7-chloro-N-(4-(prop-2-ynylamino)butyl)quinolin-4-amine ( 7 ) : Yield: 62%, mp = 72°C.
Synthesis of terminal azide
Synthesis of methyl 3α,7α,12α-trihydroxy-5β-cholane-24-oate (9)
Compound 9 was synthesized in overall good yield starting from bile acid 8 using the literature procedure . White solid, m.p. 158°C.
Methyl-3α-mesyloxy-7α-12α-dihydroxy-5β-cholane-24-oate ( 10 ) : To a solution of 9 (2.0 g, 4.92 mmol) in CH2Cl2 (20 mL) was added triethylamine (6.4 mL, 49.2 mmol) at 0°C. Methane sulfonyl chloride (0.5 mL, 4.92 mmol) was added dropwise for 10 min at 0°C. The reaction mixture was extracted with CH2Cl2/H2O. Organic layer was washed with NaHCO3, water, and brine. The solvent was evaporated under reduced pressure. The crude product was purified by column chromatography (AcOEt/Hex 2:8) to obtain pure product 7 (1.9 g).
Synthesis of methyl-3β-azido-7α,12α-dihydroxy-5β-cholane-24-oate (11)
The compound 10 was reacted with NaN3 (5 equiv) in DMF for 24 h at 120°C to give product 11 . White solid, m.p. 175°C.
General procedure for cycloaddition (12–14)
The alkyne 3, 5, or 7 (1 equiv) and the azide 11 (1.3 equiv) were dissolved in DMSO/H2O 4:1 (5 mL). To this solution, CuSO4.5H2O (0.05 equiv) and sodium ascorbate (0.40 equiv) were added. The reaction mixture was stirred for 48 h at room temperature and it was then extracted with CH2Cl2/H2O. Organic layer was washed with NaHCO3, water, and brine. The solvent was evaporated under reduced pressure and crude product was purified by column chromatography on silica gel using 30% MeOH/CH2Cl2 system to obtain aminoquinoline/bile acid conjugates 12, 13, or 14, respectively, linked with 1,4-disubstituted 1,2,3-triazole in 60% yield.
Methyl 3β-(N-[(7-chloroquinolin-4-yl)amino]ethylaminomethyl)-1 H-1,2,3-triazol-1-yl)]7α-12α-dihydroxy-5β-cholane-24-oate ( 12 ): Yellow crystalline solid; m.p. 128°C, υmax (KBr): 3340 (NH), 2930 (CH); 1 H NMR (300 MHz, CD3OD): 8.31 (d, 1 H, J 2,3 = 4 Hz, H-2’); 8.08 (d, 1 H, J 5,6 = 6 Hz, H-5’); 7.88 (s, 1 H, H-4” triazole); 7.73 (s, 1 H, H-8’); 7.37 (dd, 1 H, J 6,5 = 6 Hz, J = 2 Hz, H-6’); 6.51 (d, 1 H, J 3,2 = 4 Hz, H-3’); 4.53 (s, 1 H, H-12); 3.60 (s, 1 H, H-7); 3.89 (s, 2 H, H-3”); 3.49 (s, 3 H, H-25); 3.45 (m, 2 H, H-1”); 2.93 (m, 2 H, H-2”); 0.97 (d, 3 H, J = 6 Hz, H-21); 0.76 (s, 3 H, H-18); 0.65 (s, 3 H, H-19); 13C NMR (75 MHz, CD3OD): 176.4 (C-24); 152,6 (C-4’); 152.0 (C-2’); 149.3 (C-9’); 146.3 (C-3” triazole); 136.3 (C-7’); 127.3 (C-8’); 125.9 (C-6’); 124.3 (C-4” triazole); 123.3 (C-5’); 118.6 (C-10’); 99.5 (C-3’); 73.7 (C-12); 68.7 (C-7); 58.2 (C-3); 51.8 (C-13); 48.8 (C-25); 47.1 (C-2); 23.3 (C-21); 17.4 (C-19); 12.8 (C-18); HRMS ESI [M + H]+: m/z: Calc for C39H56N6O4Cl 707.4052 [M + H]+, found 707.4059 [M + H]+.
Methyl 3β-(N-[(7-chloroquinolin-4-yl)amino]propylaminomethyl)-1 H-1,2,3-triazol-1-yl)]7α-12α-dihydroxy-5β-cholane-24-oate ( 13 ): Yellow oil; υmax (KBr): 3345 (NH), 2928 (CH); 1 H NMR (300 MHz, CDCl3): 8.38 (d, 1 H, J 2,3 = 4 Hz, H-2’); 7.87 (s, 1 H, H-8’); 7.74 (d, 1 H, J 5,6 = 6 Hz, H-5’); 7.52 (s, 1 H, H-5” triazole); 7.20 (dd, 1 H, J 6,5 = 6 Hz, J = 2 Hz, H-6’); 6.27 (d, 1 H, J 3,2 = 4 Hz, H-3’); 4.53 (s, 2 H, H-4”); 3.87 (s, 1 H, H-7); 3.65 (s, 3 H, H-25); 3.45 (m, 2 H, H-1”); 0.97 (d, 3 H, J = 6 Hz, H-21); 0.81 (s, 3 H, H-18); 0.68 (s, 3 H, H-19); 13C NMR (75 MHz, CDCl3): 174.9 (C-24); 151.4 (C-4’); 150.2 (C-2’); 144.6 (C-9’); 144.6 (C-4” triazole); 135.5 (C-7’); 126.8 (C-8’); 125.4 (C-6’); 123.0 (C-5” triazole); 122.9 (C-5’); 121.4 (C-10’), 114.0 (C-3’), 73.0 (C-12), 68.2 (C-7), 57.0 (C-3), 51.7 (C-13), 48.4 (C-25), 47.4 (C-2), 38.3 (C-14); 22.9 (C-21); 17.5 (C-19); 12.7 (C-18); HRMS ESI [M + H]+: m/z: Calc for C40H58N6O4Cl 721.4108 [M + H]+, found 721.4210 [M + H]+.
Methyl 3β-(N-[(7-chloroquinolin-4-yl)amino]buthylaminomethyl)-1 H-1,2,3-triazol-1-yl)]7α-12α-dihydroxy-5β-cholane-24-oate ( 14 ).
Yellow oil; υmax (KBr): 3347 (NH), 2931 (CH); 1 H NMR (300 MHz, CDCl3): 8.44 (d, 1 H, J 2,3 = 2 Hz, H-2’); 7.88 (s, 1 H, H-8’); 7.77 (d, 1 H, J 5,6 = 6 Hz, H-5’); 7.51 (s, 1 H, H-7” triazol); 7.23 (dd, 1 H, J 6,5 = 6 Hz, J = 2 Hz, H-6’); 6.32 (d, 1 H, J 3,2 = 2 Hz, H-3’); 3.92 (s, 2 H, H-4”); 3.88 (s, 1 H, H-7); 3.66 (s, 3 H, H-25); 3.28 (m, 2 H, H-1”); 0.99 (d, 3 H, J = 6 Hz, H-21); 0.82 (s, 3 H, H-18); 0.68 (s, 3 H, H-19); 13C NMR (75 MHz, CDCl3): 174.9 (C-24); 151.6 (C-4’); 150.5 (C-2’); 148.7 (C-9’); 145.3 (C-6” triazole); 134.8 (C-7’); 127.8 (C-8’); 124.9 (C-6’); 122.3 (C-7” triazole); 121.2 (C-5’); 117.4 (C-10’); 98.8 (C-3’); 72.9.0 (C-12); 68.0 (C-7); 56.9 (C-3); 51.6 (C-13); 48.7 (C-25); 47.3 (C-2); 22.9 (C-21); 17.5 (C-19); 12.7 (C-18); HRMS ESI [M + H]+: m/z: Calc for C41H60N6O4Cl 735.4365 [M + H]+, found 735.4362 [M + H]+.
The anti-MTB activity of the compounds was determined by the Resazurin Microtiter Assay (REMA) . Stock solutions of the test compounds were prepared in dimethyl sulfoxide (DMSO) and diluted in Middlebrook 7 H9 broth (Difco), supplemented with oleic acid, albumin, dextrose and catalase (OADC enrichment—BBL/Becton Dickinson, Sparks, MD, USA), to obtain final drug concentration ranges from 0.15 to 250 μM. The serial dilutions were realized in a Precision XS Microplate Sample Processor (Biotek™). The isoniazid was dissolved in distilled water, as recommended by the manufacturer (Difco laboratories, Detroit, MI, USA), and used as a standard drug. MTB H37Rv ATCC 27294 was grown for 7 to 10 days in Middlebrook 7 H9 broth supplemented with OADC, plus 0.05% Tween 80 to avoid clumps. Cultures were centrifuged for 15 min at 3,150 g, washed twice, and resuspended in phosphate-buffered saline and aliquots were frozen at −80°C. After 2 days, an aliquot was thawed to determine the viability and the CFU after freezing. MTB H37Rv (ATCC 27294) was thawed and added to the test compounds, yielding a final testing volume of 200 μL with 2 × 104 CFU/mL. Microplates with serial dilutions of each compound were incubated for 7 days at 37°C, after resazurin was added to test viability. Wells that turned from blue to pink, with the development of fluorescence, indicated growth of bacterial cells, while maintenance of the blue color indicated bacterial inhibition . The fluorescence was read (530 nm excitation filter and 590 nm emission filter) in a SPECTRAfluor Plus (Tecan®) microfluorimeter. The MIC was defined as the lowest concentration resulting in 90% inhibition of growth of MTB. As a standard test, the MIC of isoniazid was determined on each microplate. The acceptable range of isoniazid MIC is from 0.11 to 0.44 μM [10, 33]. Each test was set up in triplicate.
In vitro antileishmanial activity
Parasites and cell culture
Promastigote forms of L. major (MRHO/SU/59/P) were maintained in Medium BHI supplemented with 10% fetal bovine serum (FBS) at 24°C. FBS was purchased from Cultilab (Campinas, São Paulo, Brazil) and brain heart infusion (BHI) from Himédia (Mumbai, India).
The viability of parasites was determined by the colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (purchased by Sigma Chemical Co., St. Louis, MO, USA) or MTT method, based on tetrazolium salt reduction by mitochondrial dehydrogenases . Briefly, promastigotes of L. major from a logarithmic phase culture were suspended to yield 2 million cells/mL after Neubauer chamber counting. The screening was performed in 96-well microtiter plates maintained at 24°C. Controls with DMSO and without drugs were performed. Absorbance was measured at 570 nm (Multiskan MS microplate reader, LabSystems Oy, Helsink, Finland). The results are expressed as the concentrations inhibiting parasite growth by 50% (IC50) after a 3-day incubation period. Amphotericin B (supplied by Cristália, São Paulo, Brazil) was used as the reference standard. For data analysis: IC50 values were carried out at 5% significance level (p < 0.05, CI 95%), calculated using a nonlinear regression curve, by using GraFit Version 5 software (Erithacus Software Ltd., Horley, UK).
Concerning the amastigotes in vitro model, inflammatory macrophages were obtained from BALB/c mice previously inoculated with 3% thioglycollate medium (Sigma Chemical Co.). Briefly, peritoneal macrophages were plated at 2 × 106 cells/mL on coverslips (13-mm diameter) previously arranged in a 24-well plate in RPMI 1640 medium supplemented with 10% inactivated FBS, and allowed to adhere for 24 h at 37°C in 5% CO2. Adherent macrophages were infected with L. major (MRHO/SU/59/P) promastigotes in the stationary growth phase using a ratio of 1:10 at 37°C for 3 h. Non-internalized promastigotes were eliminated and solutions of tested compounds were added and maintained at 37°C in 5% CO2 for 72 h. Slides were fixed and stained with Giemsa for parasite counting (optical microscopy, 1000× magnification). Amphotericin B was used as a standard drug and the reduction of the number of amastigotes was evaluated after only 24-h post-infection (0.1 μM = 35% and 1.0 μM = 48% of reduction of intracellular amastigotes). The data were analyzed using GraphPad Prism 5.0 (GraphPad Software, San Diego, CA, USA), which considered the mean of two assays performed in duplicate. One-way ANOVA was applied to compare all the groups. Differences were regarded as significant when p < 0.0001 (***) and p < 0.001 (**).
Results and discussion
Effect of the compounds on promastigote forms of L. major, murine peritoneal macrophages and M. tuberculosis
Biological tests (μM)
M. tuberculosis(MIC) a
L. major(IC 50) b
Anti-MTB activity of the compounds increased in the following order: alkyne intermediate structures (3, 5, and 7) < aminoquinoline/steroid conjugates (12–14). The aminoquinoline/steroid conjugates (12–14) showed excellent results with MICs ranging from 8.8 to 17.3 μM. Within these conjugates, the compound 12 was the most active against MTB bacilli (8.8 μM) and the presence of the shortest ethylenodiamine linker was enough to demonstrate the improved activity. The minimum inhibitory concentration (MIC) value found for the compound 12 is comparable or better than the MIC of some “second-line” drugs currently used in TB therapy such as cycloserine (122.4–489.7 μM), kanamycin (2.1–8.6 μM), tobramycin (8.6–17.1 μM), and clarithromycin (10.7–21.4 μM) .
For antileishmanial test, the assay was performed in both promastigote and amastigote forms of Leishmania since both stages of parasite are used for drug screening research [32–34]. Table 1 shows IC50 values of synthesized compounds on promastigote forms of L. major. Aminoquinoline/steroid conjugates (12–14) were more active than the respective alkyne intermediate structures (3, 5, and 7, respectively). Among them, the compound 12 was the most active in promastigotes of L. major, inhibiting two times more the viability of the parasite than the alkyne intermediate 3.
Antileishmanial and anti-MTB results confirm the importance of steroid groups such cholic acid acting as carriers. The cholic acid-derived carriers can possibly increase the solubility in physiological conditions and it could lead to increased cell permeability due to the amphiphilic character of the molecule and could function as an ionophore . Further in vivo mouse model studies could better elucidate the role of bile acid derivatives as carriers.
Regioselective synthesis of the novel aminoquinoline/steroid conjugates was achieved in very high yield. Addition of a steroid group to aminoquinoline molecules enhanced the anti-MTB activity, having lower MICs than some drugs commonly used to treat TB. For antileishmanial assay, the aminoquinoline/steroid conjugates demonstrated a significant activity against promastigote and amastigote forms of L. major.
Brain heart infusion
Fetal bovine serum
- IC50 :
Concentrations inhibiting parasite growth by 50%
Minimum inhibitory concentration
This study was supported by the FAPEMIG, FAPESP, CAPES, CNPq and BIC/UFJF.
- Kaur K, Jain M, Reddy RP, Jain R: Quinolines and structurally related heterocycles as antimalarials. Eur J Med Chem 2010, 45: 3245. 10.1016/j.ejmech.2010.04.011View ArticleGoogle Scholar
- Kaur K, Jain M, Khan SI, Jacob MR, Tekwani BL, Singh S, Singh PP, Jain R: Synthesis, antiprotozoal, antimicrobial, β-hematin inhibition, cytotoxicity and methemoglobin (MetHb) formation activities of bis(8-aminoquinolines). Bioorg Med Chem 2011, 19: 197. 10.1016/j.bmc.2010.11.036View ArticleGoogle Scholar
- Vieira NC, Herrenknecht C, Vacus J, Fournet A, Bories C, Figadère B, Espindola LS, Loiseau PM: Selection of the most promising 2-substituted quinoline as antileishmanial candidate for clinical trials. Biomed Pharmacother 2008, 62: 684. 10.1016/j.biopha.2008.09.002View ArticleGoogle Scholar
- Tekwani BL, Walker LA: 8-Aminoquinolines: future role as antiprotozoal drugs. Curr Opin Infect Dis 2006, 19: 623. 10.1097/QCO.0b013e328010b848View ArticleGoogle Scholar
- Kaur K, Patel SR, Patil P, Jain M, Khan SI, Jacob MR, Ganesan S, Tekwani BL, Jain R: Synthesis, antimalarial, antileishmanial, antimicrobial, cytotoxicity, and methemoglobin (MetHB) formation activities of new 8-quinolinamines. Bioorg Med Chem 2007, 15: 915. 10.1016/j.bmc.2006.10.036View ArticleGoogle Scholar
- World Health Organization: Leishmaniasis. . Accessed May 16, 2011 http://www.who.int/leishmaniasis/en/
- Baiocco P, Colotti G, Franceschini S, Ilari A: Molecular basis of antimony treatment in leishmaniasis. J Med Chem 2009, 23: 2603.View ArticleGoogle Scholar
- Koul A, Arnoult E, Lounis N, Guillemont J, Andries K: The challenge of new drug discovery for tuberculosis. Nature 2011, 469: 483. 10.1038/nature09657View ArticleGoogle Scholar
- Gandhi NR, Nunn P, Dheda K, Schaaf HS, Zignol M, van Soolingen D, Jensen P, Bayona J: Multidrug-resistant and extensively drug-resistant tuberculosis: a threat to global control of tuberculosis. Lancet 2010, 22: 1830.View ArticleGoogle Scholar
- Pavan FR, Poelhsitz GV, Do Nascimento FB, Leite SR, Batista AA, Deflon VM, Sato DN, Franzblau SG, Leite CQ: Ruthenium (II) phosphine/picolinate complexes as antimycobacterial agents. Eur J Med Chem 2010, 45: 598. 10.1016/j.ejmech.2009.10.049View ArticleGoogle Scholar
- Barry CE, Slayden RA, Sampson AE, Lee RE: Use of genomics and combinatorial chemistry in the development of new antimycobacterial drugs. Biochem Pharmacol 2000, 59: 221. 10.1016/S0006-2952(99)00253-1View ArticleGoogle Scholar
- Hermanson GT: Bioconjugate techniques. San Diego: Academic; 1996.Google Scholar
- Breinbauer R, Kohn M: Azide-alkyne coupling: a powerful reaction for bioconjugate chemistry. Chembiochem 2003, 4: 1147. 10.1002/cbic.200300705View ArticleGoogle Scholar
- Kharb R, Sharma PC, Yar MS: Pharmacological significance of triazole scaffold. J Enz Inhib Med Chem 2011, 26: 1. 10.3109/14756360903524304View ArticleGoogle Scholar
- Bhat L, Jandeleit B, Dias TM, Moors TL, Gallop MA: Synthesis and biological evaluation of novel steroidal pyrazoles as substrates for bile acid transporters. Bioorg Med Chem Lett 2005, 15: 85. 10.1016/j.bmcl.2004.10.027View ArticleGoogle Scholar
- Savage PB, Li C: Cholic acid derivatives: novel antimicrobials. Exp Opin Investig Drugs 2000, 9: 263. 10.1517/135437126.96.36.1993View ArticleGoogle Scholar
- Bavikar SN, Salunke DB, Hazra BG, Pore VS, Dodd RH, Thierry J, Shirazi F, Deshpande MV, Kadreppa S, Chattopadhyay S: Synthesis of chimeric tetrapeptide-linked cholic acid derivatives: impending synergistic agents. Bioorg Med Chem Lett 2008, 18: 5512. 10.1016/j.bmcl.2008.09.013View ArticleGoogle Scholar
- Pore VS, Aher NG, Kumar M, Shukla PK: Design and synthesis of fluconazole/bile acid conjugate using click reaction. Tetrahedron 2006, 62: 11178. 10.1016/j.tet.2006.09.021View ArticleGoogle Scholar
- Enhsen A, Kramer W, Wess G: Bile acids in drug discovery. Drug Discov Today 1998, 3: 409. 10.1016/S1359-6446(96)10046-5View ArticleGoogle Scholar
- Kannan A, De Clercq E, Pannecouque C, Witvrouw M, Hartman TL, Turpin JA, Buckheit RW, Cushman M: Synthesis and anti-HIV activity of a bile acid analog of cosalane. Tetrahedron 2001, 57: 9385. 10.1016/S0040-4020(01)00955-3View ArticleGoogle Scholar
- Anelli PL, Lattuada L, Lorusso V, Lux G, Morisetti A, Morosini P, Serleti M, Uggeri FJJ: Conjugates of gadolinium complexes to bile acids as hepatocyte-directed contrast agents for magnetic resonance imaging. J Med Chem 2004, 47: 3629. 10.1021/jm0310683View ArticleGoogle Scholar
- Solaia BA, Terzic N, Pocsfalvi G, Gerena L, Tinant B, Opsenica D, Milhous WKJ: Mixed steroidal 1,2,4,5-tetraoxanes: antimalarial and antimycobacterial activity. Med Chem 2002, 45: 3331. 10.1021/jm020891gView ArticleGoogle Scholar
- Salunke DB, Hazra BG, Pore VS: Steroidal conjugates and their pharmacological applications. Curr Med Chem 2006, 13: 813. 10.2174/092986706776055562View ArticleGoogle Scholar
- Carmo AML, Silva FMC, Machado PA, Fontes AP, Pavan FR, Leite CQ, Leite SR, Coimbra ES, Da Silva AD: Synthesis of 4-aminoquinoline analogues and their platinum(II) complexes as new antileishmanial and antitubercular agents. Biomed Pharmacother 2011, 65: 204. 10.1016/j.biopha.2011.01.003View ArticleGoogle Scholar
- De Souza NB, Carmo AML, Lagatta DC, Alves MJM, Fontes APS, Coimbra ES, Da Silva AD, Abramo C: 4-aminoquinoline analogues and its platinum (II) complexes as antimalarial agents. Biomed Pharmacother 2011, 65: 313. 10.1016/j.biopha.2011.03.003View ArticleGoogle Scholar
- Palomino JC, Martin A, Camacho M, Guerra H, Swings J, Portaela F: Resazurin microtiter assay plate: simple and inexpensive method for detection of drug resistance in Mycobacterium tuberculosis. Antimicrob Agents Chemother 2002, 46: 2720. 10.1128/AAC.46.8.2720-2722.2002View ArticleGoogle Scholar
- Mossman T: Rapid colorimetric assay for cellular growth and survival: application to proliferation and cytotoxicity assays. J Immunol Meth 1983, 65: 55. 10.1016/0022-1759(83)90303-4View ArticleGoogle Scholar
- Musonda CC, Gut J, Rosenthal PJ, Yardley V, de Souza RCC, Chibale K: Application of multicomponent reactions to antimalarial drug discovery. Part 2. New antiplasmodial and antitrypanosomal 4-aminoquinoline gamma- and delta-lactams via a 'catch and release protocol. Bioorg Med Chem 2006, 14: 5605. 10.1016/j.bmc.2006.04.035View ArticleGoogle Scholar
- Aher NG, Pore VS: Synthesis of Bile Acid Dimers Linked with 1,2,3- Triazole Ring at C-3, C-11, and C-24 Positions. Synlett 2005, 14: 2155.Google Scholar
- Salunke DB, Hazra BG, Pore VS, Bhat MK, Nahar PB, Deshpande MV: New steroidal dimers with antifungal and antiproliferative activity. J Med Chem 2004, 47: 1591. 10.1021/jm030376yView ArticleGoogle Scholar
- Collins L, Franzblau SG: Microplate alamar blue assay versus BACTEC 460 system for high-throughput screening of compounds against Mycobacterium tuberculosis and Mycobacterium avium . Antimicrob Agents Chemother 1997, 41: 1004.Google Scholar
- Sereno D, Cordeiro da Silva A, Mathieu-Daude F, Ouassi A: Advances and perspectives in Leishmania cell based drug-screening procedures. Parasitol Int 2007, 56: 3. 10.1016/j.parint.2006.09.001View ArticleGoogle Scholar
- Vermeersch M, da Luz RI, Tote K, Timmermans JP, Cos P, Maes L: In vitro susceptibilities of Leishmania donovani promastigote and amastigote stages to antileishmanial reference drugs: practical relevance of stage-specific differences. Antimicrob Agents Chemother 2009, 53: 3855. 10.1128/AAC.00548-09View ArticleGoogle Scholar
- Tempone AG, Martins de Oliveira C, Berlinck RG: Current approaches to discover marine antileishmanial natural products. Planta Med 2011, 77: 572. 10.1055/s-0030-1250663View ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.