Ion valence-gated photochromism of an aza-crowned diarylethene.

A non-photochromic diarylethene 2o with an N-phenylaza-15-crown-5 was synthesized. When the nitrogen atom in the aza-crown ring was protonated, it became photochromic due to the prevention of a twisted intramolecular charge transfer (TICT). Although addition of a monovalent metal cation (Li+, Na+, K+, Rb+, Cs+, Cu+, Ag+) in acetonitrile could not stop the TICT so that it was not photochromic, the addition of a multivalent metal cation (Mg2+, Ca2+, Sr2+, Ba2+, Fe2+, Ni2+, Al3+, Sb5+) changed 2o to be photochromic due to the strong attraction of the lone pair on the nitrogen atom. In the presence of excess Cu2+, 2o was oxidized to be EPR-detectable 2o·+, which was thermally unstable as well as inert towards visible-light irradiation. However, 2o·+ was further oxidized to be fairly stable 2o2+ by the irradiation of 365-nm light in the presence of Cu2+. ESI-MS measurements strongly suggested the generation of 2o·+ by mixing 2o with Cu(ClO4)2 in acetonitrile, and the transformation of 2o·+ to 2o2+ by successive 365-nm light irradiation. Fe3+ similarly worked as the oxidant, but the two-step oxidation of 2o to 2o2+ occurred more easily.

Novel mimetic tissue standards for precise quantitative mass spectrometry imaging of drug and neurotransmitter concentrations in rat brain tissues.

Understanding the relationship between the concentration of a drug and its therapeutic efficacy or side effects is crucial in drug development, especially to understand therapeutic efficacy in central nervous system drug, quantifying drug-induced site-specific changes in the levels of endogenous metabolites, such as neurotransmitters. In recent times, evaluation of quantitative distribution of drugs and endogenous metabolites using matrix-assisted laser desorption/ionization (MALDI)-mass spectrometry imaging (MSI) has attracted much attention in drug discovery research. However, MALDI-MSI quantification (quantitative mass spectrometry imaging, QMSI) is an emerging technique, and needs to be further developed for practicable and convenient use in drug discovery research. In this study, we developed a reliable QMSI method for quantification of clozapine (antipsychotic drug) and dopamine and its metabolites in the rat brain using MALDI-MSI. An improved mimetic tissue model using powdered frozen tissue for QMSI was established as an alternative method, enabling the accurate quantification of clozapine levels in the rat brain. Furthermore, we used the improved method to evaluate drug-induced fluctuations in the concentrations of dopamine and its metabolites. This method can quantitatively evaluate drug localization in the brain and drug-induced changes in the concentration of endogenous metabolites, demonstrating the usefulness of QMSI.

Probing local structure of glass with orientation-dependent luminescence.

The local ordering of particles is considered an important process in glass transition. Ordering is usually observed in simulation and micrometer-sized colloid. However, clear information on local ordering at the molecular level is difficult to obtain experimentally. In this study, we prepared an easily glass-forming fluorophore with a color change owing to the intermolecular arrangement in the liquid, glass, and crystal states. The bathochromic shifts of the photoluminescence spectra indicated a change in the intermolecular orientation upon immediate cooling of the melt. The recovery of the spectra by successive heating indicated that rotation contributed to the change in the intermolecular orientation. The orientation in the glass was distinct from that during crystal growth, which was observed as a slow bathochromic shift by maintaining the temperature between the melting points of the blue- and green-luminescent crystals obtained from dichloromethane/ethanol and dichloromethane/hexane, respectively. Our results demonstrate that the anisotropic interaction between glass-forming luminophores is useful for uncovering molecular-level events in the glassy state.

Monomeric structure of an active form of bovine cytochrome c oxidase.

Cytochrome c oxidase (CcO), a membrane enzyme in the respiratory chain, catalyzes oxygen reduction by coupling electron and proton transfer through the enzyme with a proton pump across the membrane. In all crystals reported to date, bovine CcO exists as a dimer with the same intermonomer contacts, whereas CcOs and related enzymes from prokaryotes exist as monomers. Recent structural analyses of the mitochondrial respiratory supercomplex revealed that CcO monomer associates with complex I and complex III, indicating that the monomeric state is functionally important. In this study, we prepared monomeric and dimeric bovine CcO, stabilized using amphipol, and showed that the monomer had high activity. In addition, using a newly synthesized detergent, we determined the oxidized and reduced structures of monomer with resolutions of 1.85 and 1.95 Å, respectively. Structural comparison of the monomer and dimer revealed that a hydrogen bond network of water molecules is formed at the entry surface of the proton transfer pathway, termed the K-pathway, in monomeric CcO, whereas this network is altered in dimeric CcO. Based on these results, we propose that the monomer is the activated form, whereas the dimer can be regarded as a physiological standby form in the mitochondrial membrane. We also determined phospholipid structures based on electron density together with the anomalous scattering effect of phosphorus atoms. Two cardiolipins are found at the interface region of the supercomplex. We discuss formation of the monomeric CcO, dimeric CcO, and supercomplex, as well as their role in regulation of CcO activity.

On-Demand Chirality Transfer of Human Serum Albumin to Bis(thiophen-2-yl)hexafluorocyclopentenes through Their Photochromic Ring Closure.

Photochromic 1,2-bis(5-carboxy-3-methyl-2-thienyl)hexafluorocyclopentene and its dimethyl ester incorporated in human serum albumin (HSA) showed highly enantioselective photochromic ring-closing reactions upon 366 nm light irradiation. The absolute stereochemistry of the major ring-closed form of the dicarboxylic acid at the newly formed sp3 carbon atoms was determined to be (S,S) by the process of docking simulation of the diarylethene molecule and HSA followed by molecular dynamics calculations and comparison of the measured and calculated CD spectra. Esterification of the major closed form of the diacid gave the minor closed form of the diester. The absolute stereochemistry of the major diester was thus determined to be (R,R).

Applicability of the Øie-Tozer model to predict three types of distribution volume (Vd) in humans: Vd in central compartment, Vd at steady state, and Vd at beta phase.

This study aimed to investigate the applicability of the Øie-Tozer model to predict human distribution volume (Vd) in the central compartment (V1 ), Vd at steady state (Vdss ), and Vd at beta phase (Vdß ) based on animal Vd. Twenty compounds that have a human V1 /Vdss of 0.053-0.66 were selected from the literature. After intravenous administration of the compounds at 0.1 mg/kg to rats, dogs, and monkeys, plasma concentrations were determined, and pharmacokinetic parameters were obtained by one/two-compartmental analyses. The human V1 , Vdss , and Vdß were predicted from animal Vd using the Øie-Tozer model, and the predictability was compared with that using proportionality and simple allometry. The Øie-Tozer model was the most reliable method for the overall prediction of Vd and applicable for accurately predicting human V1 , Vdss , and Vdß (89%, 85%, and 68% of the compounds within a 3-fold error, respectively) when data of monkey for V1 and data of three animal species for Vdss and Vdß were used. Additionally, the predicted human Vd with the two-compartment model was applicable for predicting pharmacokinetic profiles/parameters in humans after intravenous administration of 18 compounds [except for valproic acid (monophasic elimination profile) and chlorpromazine (deviation: Vdss < V1 )]. The prediction was more accurate than that using the predicted Vdss with the one-compartment model (e.g., underestimation of maximum plasma concentrations: 2 vs 8 compounds within a 3-fold error, respectively). In summary, the Øie-Tozer model was applicable for predicting human V1 , Vdss , and Vdß , and their predicted Vd with the two-compartment model can lead to accurate pharmacokinetic prediction of compounds that show biphasic elimination.

Species differences in metabolism of a new antiepileptic drug candidate, DSP-0565 [2-(2'-fluoro[1,1'-biphenyl]-2-yl)acetamide].

The metabolism and pharmacokinetics of DSP-0565 [2-(2'-fluoro[1,1'-biphenyl]-2-yl)acetamide], an antiepileptic drug candidate, was investigated in rats, dogs, and humans. In human hepatocytes, [14 C]DSP-0565 was primarily metabolized via amide bond hydrolysis to (2'-fluoro[1,1'-biphenyl]-2-yl)acetic acid (M8), while in rat and dog hepatocytes, it was primarily metabolized via both hydrolysis to M8 and hydroxylation at the benzene ring or the benzyl site to oxidized metabolites. After single oral administration of [14 C]DSP-0565 to rats and dogs, the major radioactivity fraction was recovered in the urine (71-72% of dose) with a much smaller fraction recovered in feces (23-25% of dose). As primary metabolites in their excreta, M8, oxidized metabolites, and glucuronide of DSP-0565 were detected. The contribution of metabolic pathways was estimated from metabolite profiles in their excreta: the major metabolic pathway was oxidation (57-62%) and the next highest was the hydrolysis pathway (23-33%). These results suggest that there are marked species differences in the metabolic pathways of DSP-0565 between humans and animals. Finally, DSP-0565 human oral clearance (CL/F) was predicted using in vitro-in vivo extrapolation (IVIVE) with/without animal scaling factors (SF, in vivo intrinsic clearance/in vitro intrinsic clearance). The SF improved the underestimation of IVIVE (fold error = 0.22), but the prediction was overestimated (fold error = 2.4-3.3). In contrast, the use of SF for hydrolysis pathway was the most accurate for the prediction (fold error = 1.0-1.4). Our findings suggest that understanding of species differences in metabolic pathways between humans and animals is important for predicting human metabolic clearance when using animal SF.

A photon-working on/off switch for intramolecular donor-acceptor interactions and invisible modulation of the fluorescence.

An on/off switching for charge-transfer interactions between the side chains of a diarylethene based on photochromic reactions has been proved by the disappearance and appearance of an additional fluorescence band.

A chiral photoswitch based on enantiospecific interconversion between binaphthyl and helicenoid skeletons.

A novel chiral photoswitch composed of a binaphthyl unit and a hexafluorocyclopentene ring has been synthesized. This chiral photoswitch exhibited thermally reversible photochromism between the binaphthyl and helicenoid forms based on 6π-electrocyclization. The helicity of the binaphthyl moiety was reversed upon stereospecific photocyclization and reverted back during the thermal ring opening.

Significance of reductive metabolism in human intestine and quantitative prediction of intestinal first-pass metabolism by cytosolic reductive enzymes.

The number of new drug candidates that are cleared via non-cytochrome P450 (P450) enzymes has increased. However, unlike oxidation by P450, the roles of reductive enzymes are less understood. The metabolism in intestine is especially not well known. The purposes of this study were to investigate the significance of reductive metabolism in human intestine, and to establish a quantitative prediction method of intestinal first-pass metabolism by cytosolic reductive enzymes, using haloperidol, mebendazole, and ziprasidone. First, we estimated the metabolic activities for these compounds in intestine and liver using subcellular fractions. Metabolic activities were detected in human intestinal cytosol (HIC) for all three compounds, and the intrinsic clearance values were higher than those in human liver cytosol for haloperidol and mebendazole. These metabolic activities in HIC were NADPH- and/or NADH-dependent. Furthermore, the metabolic activities for all three compounds in HIC were largely inhibited by menadione, which has been used as a carbonyl reductase (CBR)-selective chemical inhibitor. Therefore, considering subcellular location, cofactor requirement, and chemical inhibition, these compounds might be metabolized by CBRs in human intestine. Subsequently, we tried to quantitatively predict intestinal availability (F(g)) for these compounds using human intestinal S9 (HIS9). Our prediction model using apparent permeability of parallel artificial membrane permeability assay and metabolic activities in HIS9 could predict F(g) in humans for the three compounds well. In conclusion, CBRs might have higher metabolic activities in human intestine than in human liver. Furthermore, our prediction method of human F(g) using HIS9 is applicable to substrates of cytosolic reductive enzymes.