Synthesis of deuterium-labelled 2,5-Bis(4-amidinophenyl)furan, 2,5-Bis[4-(methoxyamidino)phenyl]furan, and 2,7-diamidinocarbazole

Production of Amidinyl Radicals via UV-Vis-Light Promoted Reduction of N-Arylthiophene-2-carboxamidoximes and Application to the Preparation of Some New N-Arylthiophene-2-carboxamidines

A modern method for the preparation of some new N-arylthiophene-2-carboxamidines via amidinyl radicals generated using UV-vis-light promoting the reduction of N-arylthiophene-2-carboxamidoximes without any catalyst in a short amount of time, highly straight forward, and in an efficient manner is described. This method defeats the flaws of the conventional methods for the reduction of amidoxime derivatives to amidine derivatives, which require harsh conditions such as using a strong acid, high temperature, and expensive catalysts. Benzo[d]imidazoles, benzo[d]oxazoles, and amides can also be synthesized by applying this method. The photoproducts were analyzed by various spectroscopic and analytical techniques, including thin-layer chromatography, column chromatography, high-performance liquid chromatography, gas chromatography/mass spectrometry, IR, ¹H NMR, ¹³C NMR, and MS. Notably, the chromatographic analyses proved that the best time for the production of N-arylthiophene-2-carboxamidines is 20 min. The reaction mechanism comprising pathways and intermediates was also suggested via the homolysis of N-O and C-N bonds.

Synthesis and structure-activity relationship of novel bisindole amidines active against MDR Gram-positive and Gram-negative bacteria

A series of novel diamidines with N-substituents on an amidine N-atom were synthesized and evaluated for their cytotoxicity and in vitro antibacterial activity against a range of Gram-positive and Gram-negative bacterial strains. Based on structure-activity relationship, N-substituents with a branched chain and a shorter carbon chain on the amidine N-atom exhibited more promising activity against Gram-negative and MDR-Gram-positive bacteria; compounds 5c and 5i were the most powerful candidate compounds. Compound 5c showed greater efficacy than levofloxacin against most drug-resistant Gram-positive bacteria and exhibited broad-spectrum antibacterial activity against Gram-negative bacteria, with MIC values in the range of 2-16 μg/mL. Slightly more potent antibacterial activity against Klebsiella pneumoniae, Acinetobacter calcoaceticus, Enterobacter cloacae, and Proteus mirabilis was observed for 5i in comparison with 5c. Compound 5i also showed remarkable antibacterial activity against NDM-1-producing Gram-negative bacteria, with MIC values in the range of 2-4 μg/mL, and was superior to the reference drugs meropenem and levofloxacin. Effective antibacterial activity of 5i was also shown in vivo in a mouse model of Staphylococcus aureus MRSA strain, with an ED₅₀values of 2.62 mg/kg.

Synthesis of N-substituted aryl amidines by strong base activation of amines

We describe an efficient method for the direct preparation of N-substituted aryl amidines from nitriles and primary amines. The protocol employs activation of amines by a strong base and provides greater access to a pharmaceutically relevant functional group. This synthetic approach tolerates deactivated nitriles, nitriles with competing substitution sites, and aryl amines.

In vitro and in vivo evaluation of 28DAP010, a novel diamidine for treatment of second-stage African sleeping sickness

African sleeping sickness is a neglected tropical disease transmitted by tsetse flies. New and better drugs are still needed especially for its second stage, which is fatal if untreated. 28DAP010, a dipyridylbenzene analogue of DB829, is the second simple diamidine found to cure mice with central nervous system infections by a parenteral route of administration. 28DAP010 showed efficacy similar to that of DB829 in dose-response studies in mouse models of first- and second-stage African sleeping sickness. The in vitro time to kill, determined by microcalorimetry, and the parasite clearance time in mice were shorter for 28DAP010 than for DB829. No cross-resistance was observed between 28DAP010 and pentamidine on the tested Trypanosoma brucei gambiense isolates from melarsoprol-refractory patients. 28DAP010 is the second promising preclinical candidate among the diamidines for the treatment of second-stage African sleeping sickness.

Pharmacokinetic comparison to determine the mechanisms underlying the differential efficacies of cationic diamidines against first- and second-stage human African trypanosomiasis

Human African trypanosomiasis (HAT), a neglected tropical disease, is fatal without treatment. Pentamidine, a cationic diamidine, has been used to treat first-stage (hemolymphatic) HAT since the 1940s, but it is ineffective against second-stage (meningoencephalitic, or central nervous system [CNS]) infection. Novel diamidines (DB75, DB820, and DB829) have shown promising efficacy in both mouse and monkey models of first-stage HAT. However, only DB829 cured animals with second-stage infection. In this study, we aimed to determine the mechanisms underlying the differential efficacies of these diamidines against HAT by conducting a comprehensive pharmacokinetic characterization. This included the determination of metabolic stability in liver microsomes, permeability across MDCK and MDR1-MDCK cell monolayers, interaction with the efflux transporter MDR1 (P-glycoprotein 1 or P-gp), drug binding in plasma and brain, and plasma and brain concentration-time profiles after a single dose in mice. The results showed that DB829, an azadiamidine, had the highest systemic exposure and brain-to-plasma ratio, whereas pentamidine and DB75 had the lowest. None of these diamidines was a P-gp substrate, and the binding of each to plasma proteins and brain differed greatly. The brain-to-plasma ratio best predicted the relative efficacies of these diamidines in mice with second-stage infection. In conclusion, pharmacokinetics and CNS penetration influenced the in vivo efficacies of cationic diamidines against first- and second-stage HAT and should be considered when developing CNS-active antitrypanosomal diamidines.

CYP4F enzymes are the major enzymes in human liver microsomes that catalyze the O-demethylation of the antiparasitic prodrug DB289 [2,5-bis(4-amidinophenyl)furan-bis-O-methylamidoxime]

DB289 [2,5-bis(4-amidinophenyl)furan-bis-O-methylamidoxime] is biotransformed to the potent antiparasitic diamidine DB75 [2,5-bis(4-amidinophenyl) furan] by sequential oxidative O-demethylation and reductive N-dehydroxylation reactions. Previous work demonstrated that the N-dehydroxylation reactions are catalyzed by cytochrome b5/NADH-cytochrome b5 reductase. Enzymes responsible for catalyzing the DB289 O-demethylation pathway have not been identified. We report an in vitro metabolism study to characterize enzymes in human liver microsomes (HLMs) that catalyze the initial O-demethylation of DB289 (M1 formation). Potent inhibition by 1-aminobenzotriazole confirmed that M1 formation is catalyzed by P450 enzymes. M1 formation by HLMs was NADPH-dependent, with a Km and Vmax of 0.5 microM and 3.8 nmol/min/mg protein, respectively. Initial screening showed that recombinant CYP1A1, CYP1A2, and CYP1B1 were efficient catalysts of M1 formation. However, none of these three enzymes was responsible for M1 formation by HLMs. Further screening showed that recombinant CYP2J2, CYP4F2, and CYP4F3B could also catalyze M1 formation. An antibody against CYP4F2, which inhibited both CYP4F2 and CYP4F3B, inhibited 91% of M1 formation by HLMs. Two inhibitors of P450-mediated arachidonic acid metabolism, HET0016 (N-hydroxy-N'-(4-n-butyl-2-methylphenyl)formamidine) and 17-octadecynoic acid, effectively inhibited M1 formation by HLMs. Inhibition studies with ebastine and antibodies against CYP2J2 suggested that CYP2J2 was not involved in M1 formation by HLMs. Additionally, ketoconazole preferentially inhibited CYP4F2, but not CYP4F3B, and partially inhibited M1 formation by HLMs. We conclude that CYP4F enzymes (e.g., CYP4F2, CYP4F3B) are the major enzymes responsible for M1 formation by HLMs. These findings indicate that, in human liver, members of the CYP4F subfamily biotransform not only endogenous compounds but also xenobiotics.

Distribution and quantitation of the anti-trypanosomal diamidine 2,5-bis(4-amidinophenyl)furan (DB75) and its N-methoxy prodrug DB289 in murine brain tissue

The current epidemic of sleeping sickness, also known as human African trypanosomiasis in sub-Saharan Africa places nearly 60 million people at risk for developing this life threatening infection. Although effective treatments for early-stage sleeping sickness exist, these drugs usually require extended dosing schedules and intravenous administration. New treatments are also needed for cerebral (late) stage trypanosomiasis. 2,5-Bis(4-amidinophenyl)furan (DB75), a pentamidine analog, has potent in vitro and in vivo anti-trypanosomal activity. However, DB75 does not exhibit significant oral bioavailability and has proved to be ineffective against mouse models of late-stage sleeping sickness regardless of administration route. To circumvent the limited oral bioavailability of DB75, an N-methoxy prodrug 2,5-bis(4-amidinophenyl)furan-bis-O-methylamidoxime (DB289) was designed and developed initially as a compound to treat AIDS-related Pneumocystis carinii pneumonia (PCP). Despite excellent oral activity against early-stage sleeping sickness, oral administration of DB289 exhibited limited efficacy in mouse models of late-stage disease. DB289 has recently entered Phase II(b) clinical trials to treat primary-stage sleeping sickness in Central Africa. The current study takes advantage of the innate fluorescence of DB75 and DB289 along with specific and sensitive quantitative analyses to examine plasma and brain distribution of these compounds. Animals were dosed with intravenous DB75, oral DB289, and intravenous DB289. Following intravenous administration, DB75 was readily detectable in whole brain extracts and persisted for long periods. Fluorescence microscopy revealed that DB75 did not penetrate into brain parenchyma, however, but was sequestered within cells lining the blood-brain and blood-cerebrospinal fluid barriers. In contrast, brain tissue of mice treated with oral DB289 exhibited diffuse fluorescence within the brain parenchyma, suggesting that the prodrug was not trapped within blood-brain barrier cells (BBB). However, maximal brain concentrations of the active compound DB75 were very low (13 nmol/mg of tissue at 24 h). Intravenous administration of DB289 resulted in a qualitatively similar fluorescence pattern to oral DB289, indicating again that DB289 and DB75 were present within brain parenchyma, not only in barrier regions. Furthermore, peak DB75 tissue levels were higher (61 nmol/mg of tissue at 24 h) than with oral prodrug. The near five-fold increase in brain levels of DB289 combined with parenchymal localization of compound fluorescence after intravenous administration suggest that the unaltered prodrug penetrates the blood-brain barrier, and may be subject to in situ biotransformation. Intravenous administration of DB289 should be evaluated in mouse models of late-stage sleeping sickness.

Characterizing the fragmentation of 2,5-bis (4-amidinophenyl)furan-bis-O-methylamidoxime and selected metabolites using ion trap mass spectrometry

A novel prodrug [2,5-bis(4-amidinophenyl)furan-bis-O-methylamidoxime (DB289)] of the promising antimicrobial agent, 2,5-bis(4-amidinophenyl)furan (DB75), has excellent oral activity. It is currently undergoing phase II clinical evaluation as an orally administered drug candidate against African trypanosomiasis and Pneumocystis carinii pneumonia. The sequential product ion (MS(n)) fragmentations of DB289 and selected metabolites were characterized using ion trap mass spectrometry with electrospray ionization. An unusual homolytic bond cleavage, formation of an odd-electron ion from an even-electron ion with the loss of a radical, was commonly seen in the fragmentation patterns of DB289 and its metabolites. Both O-ethyl and N-methyl homologues of DB289 were utilized to confirm this fragmentation pathway. The labile hydrogen atoms in DB289 are readily exchanged with deuterium atoms in the solvent containing deuterium oxide (D2O) instead of water. The mass shift patterns displayed in the product ion spectra of DB289 in D2O proved useful in verifying the fragmentation pathway. Octadeuterated DB289 and DB75 (d-labeling on the diphenyl rings) showed unequivocally that the diphenylfuran moiety is not involved in the fragmentation. The fragmentation pathways uncovered in this work will facilitate structural characterization of all the metabolites produced in the metabolic activation of DB289.