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Ghrelin is a pleiotropic feeding hormone which also has a pivotal role in the central nervous system. Upon the activation of its receptor, growth hormone secretagogue receptor (GHSR), the Gα q/11 -mediated and the β-arrestin-mediated signaling pathways are activated. As the β-arrestin pathway is a potential drug target, there is a strong need for β-arrestin-biased GHSR modulators. Activation of the β-arrestin pathway should inhibit the Gα q/11 -mediated calcium flux through the internalization of the receptor. Hence, we used the antagonistic activity in the calcium assay as the first screening for the β-arrestin activation. By conducting the second screening assay for the β-arrestin activation based on extracellular signal regulated kinase (ERK) 1/2 phosphorylation, we discovered a putative β-arrestin-biased superagonist. The activity of the compound was not completely blocked with the competitive antagonist, which implies that the effect is mediated, at least partly, by allosteric binding of the compound.

Although the advantages of sp3 -rich, sterically complicated molecules in drug development have been pointed out, modern screening libraries are filled with planar, sp2 -rich components. Compounds that are sp3 -rich are difficult to synthesize, and thus we aimed to invent an efficient method to construct sp3 -rich libraries. By modifying sp3 -rich 7-azanorbornane scaffolds through click chemistry, we efficiently prepared a small set of compounds. These compounds were not only sp3 -rich, but also had sufficient "lead-like" properties in view of molecular weights and hydrophobicity. Screening assays of this library provided weak κ opioid receptor agonists and growth hormone secretagogue receptor agonists with high hit rates. These results indicate that the 7-azanorbornane scaffold may be a "privileged structure" for lead identification in drug discovery.

1,2,3,4-Tetrahydroquinolines should be applicable to the development of new pharmaceutical agents. A facile synthesis of 1,2,3,4-tetrahydroquinolines that is achieved by a photoinduced formal [4+2] cycloaddition reaction of acyclic α,β-unsaturated amides and imides with N,N-dialkylanilines under visible-light irradiation, in which a new IrIII complex photosensitizer, a thiourea, and an oxidant act cooperatively in promoting the reaction, is reported. The photoreaction enables the synthesis of a wide variety of 1,2,3,4-tetrahydroquinolines, while controlling the trans/cis diastereoselectivity (>99:1) and constructing contiguous stereogenic centers. A chemoselective cleavage of an acyclic imide auxiliary is demonstrated.

An efficient synthetic method of seven- and six-membered cycloalkenes through the generation of strained cycloalkynes and following carbomagnesiation is described. Further bond formations of the resulting cycloalkenylmagnesium intermediates with a wide variety of electrophiles enabled us to prepare diverse cycloalkene derivatives including benzoxepine analogs having a fully substituted alkene structure.

Niemann-Pick disease type C is a rare, fatal neurodegenerative disorder characterized by massive intracellular accumulation of cholesterol. In most cases, loss-of-function mutations in theNPC1gene that encodes lysosomal cholesterol transporter NPC1 are responsible for the disease, and more than half of the mutations are considered to interfere with the biogenesis or folding of the protein. We previously identified a series of oxysterol derivatives and phenanthridine-6-one derivatives as pharmacological chaperones, i.e., small molecules that can rescue folding-defective phenotypes of mutated NPC1, opening up an avenue to develop chaperone therapy for Niemann-Pick disease type C. Here, we present an improved image-based screen for NPC1 chaperones and we describe its application for drug-repurposing screening. We identified some azole antifungals, including itraconazole and posaconazole, and a kinase inhibitor, lapatinib, as probable pharmacological chaperones. A photo-crosslinking study confirmed direct binding of itraconazole to a representative folding-defective mutant protein, NPC1-I1061T. Competitive photo-crosslinking experiments suggested that oxysterol-based chaperones and itraconazole share the same or adjacent binding site(s), and the sensitivity of the crosslinking to P691S mutation in the sterol-sensing domain supports the hypothesis that their binding sites are located near this domain. Although the azoles were less effective in reducing cholesterol accumulation than the oxysterol-derived chaperones or an HDAC inhibitor, LBH-589, our findings should offer new starting points for medicinal chemistry efforts to develop better pharmacological chaperones for NPC1.

In the inverse electron-demand Diels–Alder (iEDDA) reactions between tetrazines and strained alkenes, a mixture of 1,4-dihydropyridazine isomers are formed first, and they are then oxidized to pyridazines. Although the products of these related oxidation processes converge as pyridazines, the oxidation rate is quite low with some substrates. In this study, we revealed that 1,4-dihydropyridazines formed in the iEDDA reactions were oxidized to pyridazines by simply irradiating with an ultraviolet light under an air atmosphere. Our experimental results implied that singlet oxygen was formed in the course of the reactions to oxidize the 1,4-dihydropyridazine molecules.

We applied a desilylation procedure using SO 3 H silica gel, with the surface modified by alkylsulfonic acid groups, to silylated sugar, nucleoside, and alkaloid derivatives. The treatment with SO 3 H silica gel provided desilylated products in good to excellent yield. In the reactions of sugar and nucleoside derivatives, no silyl residue was detected in the crude products, but the crude products of the reaction of alkaloids contained small amounts of silyl residues. Even though the sugar and nucleoside derivatives had a labile glycosyl and C N bond, respectively, these bonds tolerated the reaction conditions. These outcomes suggested that the desilylation procedure using SO 3 H silica gel would be applicable to the deprotection of a variety of types of compounds protected by silyl groups. In a gram scale experiment, the desilylation procedure successfully proceeded without the observation of any silyl residue in the crude product.

In the preparation of multicomponent compounds, the accumulation of components through sequential click reactions is an attractive strategy. In this work we examined the reactivity of various N-substituted 7-azanorbornenes in inverse electron-demand Diels–Alder (iEDDA) reactions with tetrazines to explore the potential of 7-azanorbornenes as clickable hub molecules. The iEDDA reaction of 7-azanorbornene is expected to proceed faster when the nitrogen atom at the 7-position is substituted with an electron-donating substituent. Contrary to this expectation, the electron-donating alkyl-bearing derivative reacted much more slowly than those bearing electron-withdrawing acyl groups. The results of DFT calculations indicate that the reaction rates correlate well with an increase in sp2 character of the 7-nitrogen atoms: The ease of conversion of the more stable exo conformer into the more reactive endo conformer may lower the activation energy of the first rate-determining hetero-Diels–Alder step. Indeed, the reaction rates of N-acylated 7-azanorbornenes, which have a more planar nitrogen atom, were found superior to those of other derivatives and comparable to those of norbornenes. Finally, we successfully labeled a tetrazine on a protein surface by fluorophore-conjugated 7-azanorbornene in the presence of other proteins.

Niemann-Pick disease type C is a fatal, progressive neurodegenerative disease mostly caused by mutations in Nieamnn-Pick type C1 (NPC1), a late endosomal membrane protein that is essential for intracellular cholesterol transport. The most prevalent mutation, I1061T (Ile to Thr), interferes with the protein folding process. Consequently, mutated but intrinsically functional NPC1 proteins are prematurely degraded via proteasome, leading to loss of NPC1 function. Previously, we reported sterol derivatives as pharmacological chaperones for NPC1, and showed that these derivatives can normalize folding-defective phenotypes of I1061T NPC1 mutant by directly binding to, and stabilizing, the protein. Here, we report a series of compounds containing a phenanthridin-6-one scaffold as the first class of non-steroidal pharmacological chaperones for NPC1. We also examined their structure-activity relationships.

Buprenorphine shows strong analgesic effects on moderate to severe pain. Although buprenorphine can be used more safely than other opioid analgesics, it has room for improvement in clinical utility. Investigation of compounds structurally related to buprenorphine should be an approach to obtain novel analgesics with safer and improved profiles compared to buprenorphine. In the course of our previous studies, we observed that derivatives obtained by cyclizing C-homomorphinans were structurally related to buprenorphine. Hence, we synthesized cyclized C-homomorphinan derivatives with various oxygen functionalities on the side chains and evaluated their in vitro pharmacological profiles for the opioid receptors. Among the tested compounds, methyl ketone 2a with an N-methyl group showed full agonistic activities for the μ and the δ receptors and partial agonistic activity for the κ receptor. These properties were similar to those of norbuprenorphine, a major metabolite of buprenorphine, which reportedly contributes to the antinociceptive effect of buprenorphine. From these results, we concluded that cyclized C-homomorphinan would be a possible lead compound to obtain novel analgesics with buprenorphine-like properties.

Although the advantages of sp

A facile method for preparing various functional cycloalkynes, including proteins incorporated with a cycloalkyne moiety, from the corresponding azides is developed. Treatment of diynes bearing strained and terminal alkyne moieties with a copper salt enabled terminal alkyne-selective click conjugation with azides, whereas a more azidophilic strained alkyne moiety was transiently protected from the click reaction via complexation with copper.

Protecting groups are indispensable in organic synthesis and there is a great need for a variety of deprotection methods. Here, we investigated the scope of the application of a deprotection procedure using SO3H silica gel, which we have previously reported as a desilylation procedure. Under these conditions, -OMOM, -OSEM, -OTHP, and -OAc groups and dimethyl acetal were cleaved. Pivaloyloxy, benzyloxy and methoxy carbonyl groups remained intact and selective deprotection of TBS groups in the presence of other protecting groups was accomplished. We succeeded in cleaving an acetyl group on a secondary alcohol in a highly polar nortropine derivative. Our findings here provide another deprotection option and would be helpful in the synthesis of multifunctional compounds.

Buprenorphine shows strong analgesic effects on moderate to severe pain. Although buprenorphine can be used more safely than other opioid analgesics, it has room for improvement in clinical utility. Investigation of compounds structurally related to buprenorphine should be an approach to obtain novel analgesics with safer and improved profiles compared to buprenorphine. In the course of our previous studies, we observed that derivatives obtained by cyclizing C-homomorphinans were structurally related to buprenorphine. Hence, we synthesized cyclized C-homomorphinan derivatives with various oxygen functionalities on the side chains and evaluated their in vitro pharmacological profiles for the opioid receptors. Among the tested compounds, methyl ketone 2a with an N-methyl group showed full agonistic activities for the μ and the δ receptors and partial agonistic activity for the κ receptor. These properties were similar to those of norbuprenorphine, a major metabolite of buprenorphine, which reportedly contributes to the antinociceptive effect of buprenorphine. From these results, we concluded that cyclized C-homomorphinan would be a possible lead compound to obtain novel analgesics with buprenorphine-like properties.

A number of hereditary diseases are caused by defective protein trafficking due to a folding defect resulting from point mutations in proteins. Ligands that bind to the folding intermediates of such mutant proteins and rescue their trafficking defects, known as pharmacological chaperones, have promise for the treatment of certain genetic diseases, including Fabry disease, cystic fibrosis, and Niemann-Pick disease type C. Here we show that this pharmacological chaperone effect can be used for ligand screening, that is, binding of candidate ligands can be detected by monitoring the ligand-mediated correction of a localization defect caused by artificially introduced point mutations of the protein of interest. Using this method, we discovered novel steroidal ligands of Niemann-Pick type C1-like 1 (NPC1L1), an intestinal cholesterol transporter that is the target of the cholesterol absorption inhibitor ezetimibe, and conducted structure-activity relationship studies. We also present data indicating that the binding site of the new ligands is distinct from both the N-terminal sterol-binding domain and the ezetimibe-binding site.

Vildagliptin is a potent, orally active inhibitor of dipeptidyl peptidase-4 (DPP-4) for the treatment of type 2 diabetes mellitus. It has been reported that vildagliptin can cause hepatic dysfunction in patients. However, the molecular-mechanism of vildagliptin-induced liver dysfunction has not been elucidated. In this study, we employed an expression microarray to determine hepatic genes that were highly regulated by vildagliptin in mice. We found that pro-inflammatory S100 calcium-binding protein (S100) a8 and S100a9 were induced more than 5-fold by vildagliptin in the mouse liver. We further examined the effects of vildagliptin and its major metabolite M20.7 on the mRNA expression levels of S100A8 and S100A9 in human hepatoma HepG2 and leukemia HL-60 cells. In HepG2 cells, vildagliptin, M20.7, and sitagliptin – another DPP-4 inhibitor – induced S100A9 mRNA. In HL-60 cells, in contrast, S100A8 and S100A9 mRNAs were significantly induced by vildagliptin and M20.7, but not by sitagliptin. The release of S100A8/A9 complex in the cell culturing medium was observed in the HL-60 cells treated with vildagliptin and M20.7. Therefore, the parental vildagliptin- and M20.7-induced release of S100A8/A9 complex from immune cells, such as neutrophils, might be a contributing factor of vildagliptin-associated liver dysfunction in humans.

Nitrosamines are potent carcinogens and toxicants in the rat and potential genotoxins in humans. They are metabolically activated by hydroxylation at an α-carbon atom with respect to the nitrosoamino group, catalyzed by cytochrome P450. However, there has been little systematic investigation of the structure-mutagenic activity relationship of N-nitrosamines. Herein, we evaluated the mutagenicity of a series of 7-azabicyclo[2.2.1]heptane N-nitrosamines and related monocyclic nitrosamines by using the Ames assay. Our results show that the N-nitrosamine functionality embedded in the bicyclic 7-azabicylo[2.2.1]heptane structure lacks mutagenicity, that is, it is inert to α-hydroxylation, which is the trigger of mutagenic events. Further, the calculated α-C-H bond dissociation energies of the bicyclic nitrosamines are larger in magnitude than those of the corresponding monocyclic nitrosamines and N-nitrosodimethylamine by as much as 20-30 kcal/mol. These results are consistent with lower α-C-H bond reactivity of the bicyclic nitrosamines. Thus, the 7-azabicyclo[2.2.1]heptane structural motif may be useful for the design of nongenotoxic nitrosamine compounds with potential biological/medicinal applications.

Cycloheptynes and cyclooctynes are efficiently generated via a sulfoxide—magnesium exchange reaction of readily synthesized 2-sulfinylcycloalkenyl triflates.

Cycloheptynes and cyclooctynes were efficiently generated via a sulfoxide–magnesium exchange reaction of readily synthesized 2-sulfinylcycloalkenyl triflates. Cycloadditions between various ynophiles and the cycloalkynes generated by this method proceeded efficiently, providing an easy method to prepare a wide range of heterocycles fused with seven- or eight-membered carbocycles.

Niemann–Pick disease type C is a fatal neurodegenerative disease, and its major cause is mutations in NPC1 gene. This gene encodes NPC1 protein, a late endosomal polytopic membrane protein required for intracellular cholesterol trafficking. One prevalent mutation (I1061T) has been shown to cause a folding defect, which results in failure of endosomal localization of the protein, leading to loss-of-function phenotype. We have previously demonstrated that several oxysterols and their derivatives act as pharmacological chaperones; binding of these compounds to NPC1I1061T mutant protein corrects the localization/maturation defect of the mutant protein. Here, we disclose detailed structure–activity relationships of oxysterol derivatives as pharmacological chaperones for NPC1I1061T mutant.

Niemann-Pick type C1-like 1 (NPC1L1) is an intestinal cholesterol transporter that is known to be the target of the cholesterol absorption inhibitor ezetimibe. We previously discovered steroidal NPC1L1 ligands by using a novel cell-based assay that employs pharmacological chaperone effect as a readout. Those steroid derivatives bound to a site different from both the sterol-binding domain and the ezetimibe-binding site, implying that they may be a novel class of NPC1L1 inhibitors with a distinct mode of action. As an extension of that work, we aimed here to find non-steroidal NPC1L1 ligands, which may be better candidates for clinical application than steroidal ligands, by using the same assay to screen our focused library of ligands for liver X receptor (LXR), a nuclear receptor that recognizes oxysterols as endogenous ligands. Here we describe identification of a novel class of NPC1L1 ligands with a ring-fused quinolinone scaffold, and an analysis of the structure–activity relationships of their derivatives as NPC1L1 ligands.

SummaryNiemann-Pick type C1 (NPC1) is a polytopic endosomal membrane protein required for efflux of LDL-derived cholesterol from endosomes, and mutations of this protein are associated with Niemann-Pick disease type C, a fatal neurodegenerative disease. At least one prevalent mutation (I1061T) has been shown to cause a folding defect, which results in failure of endosomal localization, leading to a loss-of-function phenotype. Here, we show that several oxysterols and their derivatives act as pharmacological chaperones; binding of these compounds to I1061T NPC1 corrects the localization/maturation defect of the mutant protein. Further, these compounds alleviate intracellular cholesterol accumulation in patient-derived fibroblasts, suggesting that they may have therapeutic potential. These oxysterol derivatives bind to a domain of NPC1 that is different from the known N-terminal sterol-binding domain; i.e., there is an additional sterol-binding site on NPC1.

Although many organic/inorganic compounds that release nitric oxide (NO) upon photoirradiation (phototriggered caged-NOs) have been reported, their photoabsorption wavelengths mostly lie in the UV region, because X-NO bonds (X=heteroatom and metal) generally have rather strong π-bond character. Thus, it is intrinsically difficult to generate organic compounds that release NO under visible light irradiation. Herein, the structures and properties of N-pyramidal nitrosamine derivatives of 7-azabicyclo[2.2.1]heptanes that release NO under visible light irradiation are described. Bathochromic shifts of the absorptions of these nitrosamines, attributed to HOMO (n)-LUMO (π*) transitions associated with the nonplanar structure of the N-NO moiety, enable the molecules to absorb visible light, which results in N-NO bond cleavage. Thus, these compounds are innate organic caged-NOs that are uncaged by visible light.