Discovery of non-competitive thrombin inhibitor derived from competitive tryptase inhibitor skeleton: Shift in molecular recognition resulted from skeletal conversion of carboxylate into phosphonate.

A novel series of terminal and internal phosphonate esters based on our previously developed aryl carboxylate-type tryptase selective inhibitor 1 was synthesized. The potency of these synthesized compounds was assessed in vitro with an enzyme inhibition assay using three available serine proteases, that is, tryptase, trypsin, and thrombin. The internal phosphonate derivative 6 showed potent thrombin inhibitory activity with an IC50 value of 1.0 µM, whereas it exhibited no or only weak tryptase and trypsin inhibition at 10 µM. The Lineweaver-Burk plot analysis indicates that the inhibition pattern of thrombin with 6 is non-competitive in spite of the fact that the lead carboxylate compound 1 is competitive inhibitor. Therefore, the skeletal conversion of the carboxylate into a phosphonate alters the mode of molecular recognition of these inhibitors by thrombin.

Evaluation of Oatp and Mrp2 activities in hepatobiliary excretion using newly developed positron emission tomography tracer [11C]dehydropravastatin in rats.

We developed a pravastatin derivative, sodium (3R,5R)-3,5-dihydroxy-7-((1S,2S,6S,8S)-6-hydroxy-2-methyl-8-((1-[(11)C]-(E)-2-methyl-but-2-enoyl)oxy)-1,2,6,7,8,8a-hexahydronaphthalen-1-yl)heptanoate ([(11)C]DPV), as a positron emission tomography (PET) probe for noninvasive measurement of hepatobiliary transport, and conducted pharmacokinetic analysis in rats as a feasibility study for future clinical study. Transport activities of DPV in freshly isolated rat hepatocytes and rodent multidrug resistance-associated protein 2 (rMrp2; human, MRP2)-expressing membrane vesicles were similar to those of pravastatin. Rifampicin diminished the uptake of DPV and pravastatin by the hepatocytes, with similar inhibition potency. [(11)C]DPV underwent biotransformation to produce at least two metabolites in rat, but metabolism of [(11)C]DPV occurred negligibly in human hepatocytes during a 90-minute incubation. After intravenous injection, [(11)C]DPV was mainly distributed to the liver and kidneys, where the tissue uptake clearances (CLuptake,liver and CLuptake,kidney) were blood-flow-limited (73.6 ± 4.8 and 24.6 ± 0.6 ml/min per kilogram, respectively). Systemic elimination of [(11)C]DPV was delayed in rifampicin-treated rat and an Mrp2-deficient mutant rat, Eisai hyperbilirubinemic mutant rat (EHBR). Rifampicin treatment decreased both CLuptake,liver and CLuptake,kidney of [(11)C]DPV by 30% (P < 0.05), whereas these parameters were unchanged in EHBR. Meanwhile, the canalicular efflux clearance (CLint,bile) of [(11)C]DPV, which was 12.2 ± 1.5 ml/min per kilogram in the control rat, decreased by 60% and 89% in rifampicin-treated rat and EHBR (P < 0.05), respectively. These results indicate that [(11)C]DPV is taken up into the liver by organic anion-transporting polypeptides (rodent, Oatps; human, OATP) and excreted into bile by Mrp2 in rat, and that rifampicin may inhibit Mrp2 as well as Oatps, and consequently increase systemic exposure of [(11)C]DPV. PET using [(11)C]DPV is feasible for studies prior to the future clinical investigation of OATP and MRP2 functionality, especially for personalized medicine.

Novel strategy for synthesis of substituted benzimidazo[1,2-a]quinolines.

An efficient method for the synthesis of benzimidazo[1,2-a]quinolines under transition-metal-free conditions has been developed through a cascade reaction involving sequential aromatic nucleophilic substitution and intramolecular Knoevenagel condensation reactions. This method is applicable for the synthesis of a wide range of benzimidazo[1,2-a]quinoline derivatives from readily available 2-fluoroarylaldehyde and benzimidazole substrates.

Synthesis of [(11)C]dehydropravastatin, a PET probe potentially useful for studying OATP1B1 and MRP2 transporters in the liver.

Drug transporters mediate the uptake and elimination of drugs in various organs; therefore, having knowledge of how a transporter functions in the body would play a key role in ensuring drug efficacy in in vivo systems. In this context, we designed and synthesized [(11)C]dehydropravastatin, a novel PET probe that would be potentially useful for evaluation of the functions of the OATP1B1 and MRP2 transporters, based on the use of palladium(0)-mediated rapid C-[(11)C]methylation (viz., the rapid cross-coupling between [(11)C]methyl iodide and a boron intermediate).

PET imaging-based evaluation of hepatobiliary transport in humans with (15R)-11C-TIC-Me.

UNLABELLED: It is well accepted that drug transporters play a pivotal role in hepatobiliary excretion of anionic drugs, in which drug-drug interactions and genetic polymorphisms are known to cause variations. However, PET probes for in vivo functional characterization of these transporters have not been established yet. We used PET to investigate hepatic uptake and subsequent canalicular efflux of (11)C-labeled (15R)-16-m-tolyl-17,18,19,20-tetranorisocarbacyclin methyl ester [(15R)-(11)C-TIC-Me)] in healthy subjects. METHODS: Serial PET scans of the abdominal region in healthy male subjects were obtained with or without the organic anion-transporting polypeptide (OATP) inhibitor rifampicin after intravenous injection of (15R)-(11)C-TIC-Me as a radiotracer. Venous blood samples and PET images were obtained at frequent intervals up to 30 min after administration of the PET tracer. Dynamic imaging data were evaluated by integration plots of data collected for 2-10 min and for 10-30 min after tracer administration for the determination of tissue uptake clearance and biliary efflux clearance, respectively. RESULTS: After rapid hydrolysis in blood, the acid form-(11)C-labeled (15R)-16-m-tolyl-17,18,19,20-tetranorisocarbacyclin [(15R)-(11)C-TIC]-accumulated in the liver (37% of the dose by 17 min), and the radioactivity was then excreted into the bile (6.2% by 30 min). Rifampicin (600 mg by mouth), a potent OATP inhibitor, significantly reduced the radioactivity excreted into the bile (by 44%) by inhibiting both uptake (by 45%) and subsequent canalicular efflux (by 62%). (15R)-(11)C-TIC is an in vitro substrate of OATP1B1 and OATP1B3, and clinically relevant concentrations of rifampicin inhibited uptake by OATP1B1 and OATP1B3. These results demonstrated that in humans, (15R)-(11)C-TIC-associated radioactivity is excreted into the bile by organic anion transport systems. CONCLUSION: We demonstrated that PET image analysis with (15R)-(11)C-TIC-Me is useful for investigating variations in OATP function in the human hepatobiliary transport system.

Design, synthesis, and evaluation of new type of L-amino acids containing pyridine moiety as nitric oxide synthase inhibitor.

New amino acids 7-12 were designed and synthesized as candidate inhibitors of human nitric oxide synthase (NOS). The 2-aminopyridine-containing l-amino acids 8 had potent inhibitory activity toward all of the human NOS isozymes. However, the regioisomers 9 and 10, and 2-methylpyridine-containing compound 11 had much lower inhibitory activity. Human NOS isozymes were also inhibited by 7, which lacks an amino group on the pyridine moiety. A computational docking study was carried out to investigate the mechanism of the inhibitory effect.

Evaluation of 3-substituted arginine analogs as selective inhibitors of human nitric oxide synthase isozymes.

Nitric oxide (NO), a mediator of various physiological and pathophysiological processes, is synthesized by three isozymes of nitric oxide synthase (NOS). In developing candidate clinical drugs, it is very important not to inhibit endothelial NOS, because it plays an important role in maintaining normal blood pressure and flow. Here, we describe the design, synthesis and human NOS-inhibitory activities of S-methyl-L-isothiocitrulline-based 3-substituted arginine analogs. The 3R*-methyl compound 4, which has an S-methyl isothiourea moiety, inhibited nNOS and iNOS, but not eNOS (IC(50) > 1 mM). However, the 3R*-methyl compound 7, bearing a 5-iminoethyl moiety, did not inhibit any of the NOS isozymes, although L-N-iminoethylornithine (L-NIO) potently inhibited all three. A computational docking study was carried out to investigate the mechanism of the isozyme selectivity.