Modular Synthesis of Tripeptide Analogs with an Aminobitriazole Skeleton Using Diynyl Benziodoxolone as a Trivalent Platform.

A new synthesis method of tripeptide analogs with an aminobitriazole skeleton was proposed. The method involves assembling three amino acid-derived modules at the amino group site and onto a triisopropylsilyl diynyl benziodoxolone by copper-catalyzed electrophilic diynylation of amino acid-derived sulfonamides, chemoselective azide-alkyne cycloadditions with amino acid-derived azides, and deprotection. Various complex aminobitriazoles substituted with pyrene, nucleoside, and N-acetylglucosamine were also synthesized. The produced aminobitriazoles have three sp3 chiral centers and a C-N axial chirality.

5-N-Arylaminothiazoles with pyridyl groups and their first-row transition metal complexes: synthesis, photophysical properties, and Zn sensing.

A series of 5-N-arylaminothiazoles were synthesized with facile diversity-oriented synthesis from readily available starting materials via the reaction of thioamide dianions and thioformamides. The introduction of various substituents at the 2-position of a thiazole ring (i.e., 2-pyridyl, 4-methylpyridyl, and phenyl groups) and on the nitrogen atom (i.e., p-tolyl and phenyl groups) significantly influenced the absorption and emission spectra of the isolated compounds. X-ray analysis confirmed that the substituents at the amino site were twisted from a thiazole ring, while the formation of its nickel complex showed dinuclear metal complexes bridged with chlorine atoms. Moreover, the formation of zinc-thiazole complexes showed enhanced emission properties in solution and noticeable emission in a solid state. In addition, thiazole-bridged dypyrromethene type ligands showed high selectivity toward Zn+2, which make them good candidates for zinc sensing.

Boron complexes of thiazole-bridged 1,5-bidentate nitrogen ligands: synthesis and acid-responsive photophysical properties.

Boron complexes of 1,5-bidentate nitrogen ligands with a thiazole linker were synthesized by the halogenation of 5-H thiazoles followed by Buchwald-Hartwig amination and complexation with BF3·Et2O. These boron complexes showed a large Stokes shift of up to 125 nm, which is in marked contrast to that observed for ordinary BODIPYs. The absorption and emission spectra of the boron complexes were almost independent of the substituents in the complexes as well as the solvents used for the measurement. The nitrogen atom of the pyridyl group attached to the thiazole ring acted as a Lewis base which accepted Lewis and Brønsted acids to lead to a prominent red-shift of the absorption bands. Addition of tris(pentafluorophenyl)borane, B(C6F5)3, to the boron complex led to a significant red-shift of the absorption band. Likewise, addition of triflic acid (TfOH) and trifluoroacetic acid (TFA) resulted in the emergence of a new absorption band at a longer wavelength accompanied by fluorescence quenching phenomena. DFT calculations show that the energy gap between HOMO and LUMO of the complex significantly decreases after protonation of the nitrogen atom in the acceptor unit of the boron complex.

N-Alkenylation of hydroxamic acid derivatives with ethynyl benziodoxolone to synthesize cis-enamides through vinyl benziodoxolones.

The stereoselective synthesis of cis-ß-N-alkoxyamidevinyl benziodoxolones (cis-ß-N-RO-amide-VBXs) from O-alkyl hydroxamic acids in the presence of an ethynyl benziodoxolone-acetonitrile complex (EBX-MeCN) is reported herein. The reaction was performed under mild conditions including an aqueous solvent, a mild base, and room temperature. The reaction tolerated various O-alkyl hydroxamic acids derived from carboxylic acids, such as amino acids, pharmaceuticals, and natural products. Vinyl dideuterated cis-ß-N-MeO-amide-VBXs were also synthesized using deuterium oxide as the deuterium source. Valine-derived cis-ß-N-MeO-amide-VBX was stereospecifically derivatized to hydroxamic acid-derived cis-enamides without the loss of stereoselectivity or reduction in the deuterium/hydrogen ratio.

Chemoselective and Stereoselective Alcoholysis of Binaphthyl Phosphonothioates: Straightforward Access to Both Stereoisomers of Biologically Relevant P-Stereogenic Phosphonothioates.

P-Stereogenic phosphonothioates have attracted great attention due to their potent biological activities as analogues of phosphoric acids and phosphorothioates. We demonstrate here straightforward access to P-stereogenic phosphonothioates through the use of binaphthyl phosphonothioates as a chiral template. The first-step alcoholysis of binaphthyl phosphonothioates proceeded via a transfer of the axial chirality of a binaphthyl group to the central chirality of a phosphorus atom to give only monoalcohol adducts with moderate to excellent diastereoselectivities. Further alcoholysis of the obtained products in the presence of a small excess of alcohol and base proceeded with complete elimination of a binaphthyl group to give the corresponding P-stereogenic phosphonothioates with high enantiomeric excess. A DFT study of the reaction mechanisms in first-step alcoholysis indicated that the coordination of a sulfur atom to a sodium cation is the key factor in controlling the diastereoselectivities. This method can be applied to prepare both stereoisomers of a G6P analogue with high diastereomeric purity.

Synthesis of cis-ß-Amidevinyl Benziodoxolones from the Ethynyl Benziodoxolone-Chloroform Complex and Sulfonamides.

The synthesis of cis-ß-amidevinyl benziodoxolones from the ethynyl benziodoxolone-chloroform complex and sulfonamides is reported. Evidence indicates that highly reactive unsubstituted ethynyl benziodoxolone undergoes Michael addition of sulfonamides, including sterically demanding acyclic amino acid derivatives. The synthesis of selectively deuterated cis-ß-amidevinyl benziodoxolones and investigation of ethynyl-λ3-iodane reactivity are also described.

Synthesis, Characterization, and Reactivity of an Ethynyl Benziodoxolone (EBX)-Acetonitrile Complex.

The synthesis of a crystalline ethynyl-1,2-benziodoxol-3(1 H)-one (EBX)-acetonitrile complex is described. EBX has been widely used as an active species for a variety of reactions; however, its high instability has so far prevented its isolation. The EBX-acetonitrile is self-assembled into a double-layered honeycomb structure through weak hypervalent iodine secondary interactions and hydrogen bonding. The N-ethynylation of a variety of sulfonamides using the EBX-acetonitrile complex as a substrate under mild conditions is also described.

Sequential Deprotonation-Alkylation of Binaphthyloxy-Substituted Phosphonochalcogenoates: Chiral Tri- and Tetrasubstituted Carbon Centers Adjacent to a Phosphorus Atom.

Sequential deprotonation and alkylation of 1,1'-binaphthyloxy-substituted phosphonoselenoates and phosphonates resulted in the diastereoselective formation of chiral tri- and tetrasubstituted carbon centers adjacent to a phosphorus atom.

5-N-Arylaminothiazoles as Highly Twisted Fluorescent Monocyclic Heterocycles: Synthesis and Characterization.

A series of 5-N-arylaminothiazoles was prepared by reacting thioamide dianions derived from secondary thioamides with thioformamides, followed by sequential oxidation with iodine. X-ray analyses demonstrated that they adopt structures that are highly twisted from planar conformations. Their orientations were tuned by the steric and/or electronic interactions of the substituents at their 2-, 4-, and 5-positions. The 5-aminothiazoles exhibited a range of fluorescent emissions, from blue to orange. Although the absorption spectra were independent of the polarity of the solvent, fluorescent emissions were influenced by the polarity of the solvent: in more polar solvents, the emissions were red-shifted. These phenomena were examined in terms of Lippert-Mataga plots and the change in the dipole moment between the ground and excited states. They also exhibited emissions in the solid state, again from blue to orange. Cyclic voltammetry of the 5-aminothiazoles showed reversible waves of one-electron oxidation. The half-potential of the oxidation was reduced by the introduction of electron-donating groups to the phenyl groups on the nitrogen atom at the 5-position. DFT calculations were carried out to determine the energy levels of the HOMO and LUMO. Finally, the results of TG-DTA showed that they are thermally stable.

α-Hydroxy and α-Oxo Selenoamides: Synthesis via Nucleophilic Selenocarbamoylation of Carbonyl Compounds and Characterization.

Carbonyl compounds were added to selenocarbamoyllithiums to generate α-hydroxy and α-oxo selenoamides. Their conformations were determined by X-ray analyses. These compounds adopted conformations that were almost identical to those of ordinary amides. Unlike the consistency of the chemical shifts of the C═Se groups of the selenoamides in (13)C NMR spectra and the (1)J coupling constants of the C═Se groups, the substituents far from the selenium atom influenced the chemical shifts in (77)Se NMR.

Reaction of selenoamide dianions with thio- and selenoformamides leading to the formation of 5-aminoselenazoles: photophysical and electrochemical properties.

5-Amino-2-selenazolines were synthesized by reacting selenoamide dianions generated from secondary selenoamides and BuLi with tertiary thio- and selenoformamides followed by treatment with iodine. The resulting 5-amino-2-selenazolines were further oxidized with iodine to give 5-aminoselenazoles in moderate to good yields. The general tendencies in the (77)Se NMR spectra of the starting selenoamides, 5-amino-2-selenazolines, and 5-aminoselenazoles were determined. The chemical shifts of these compounds were highly influenced by the skeletons involving the selenium atom as well as the substituents on the carbon atoms of each skeleton. The molecular structures of 5-aminoselenazoles were clarified by X-ray analyses, and their electronic structures were elucidated by DFT calculations. Finally, UV-vis and fluorescence spectroscopy and cyclic voltammetry (CV) of 5-aminoselenazoles were performed, and their properties are discussed in relation to the substituents on the selenazole rings.

Porphyromonas gingivalis-derived lysine gingipain enhances osteoclast differentiation induced by tumor necrosis factor-α and interleukin-1ß but suppresses that by interleukin-17A: importance of proteolytic degradation of osteoprotegerin by lysine gingipain.

Periodontitis is a chronic inflammatory disease accompanied by alveolar bone resorption by osteoclasts. Porphyromonas gingivalis, an etiological agent for periodontitis, produces cysteine proteases called gingipains, which are classified based on their cleavage site specificity (i.e. arginine (Rgps) and lysine (Kgps) gingipains). We previously reported that Kgp degraded osteoprotegerin (OPG), an osteoclastogenesis inhibitory factor secreted by osteoblasts, and enhanced osteoclastogenesis induced by various Toll-like receptor (TLR) ligands (Yasuhara, R., Miyamoto, Y., Takami, M., Imamura, T., Potempa, J., Yoshimura, K., and Kamijo, R. (2009) Lysine-specific gingipain promotes lipopolysaccharide- and active-vitamin D3-induced osteoclast differentiation by degrading osteoprotegerin. Biochem. J. 419, 159-166). Osteoclastogenesis is induced not only by TLR ligands but also by proinflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin (IL)-1ß, and IL-17A, in inflammatory conditions, such as periodontitis. Although Kgp augmented osteoclastogenesis induced by TNF-α and IL-1ß in co-cultures of mouse osteoblasts and bone marrow cells, it suppressed that induced by IL-17A. In a comparison of proteolytic degradation of these cytokines by Kgp in a cell-free system with that of OPG, TNF-α and IL-1ß were less susceptible, whereas IL-17A and OPG were equally susceptible to degradation by Kgp. These results indicate that the enhancing effect of Kgp on cytokine-induced osteoclastogenesis is dependent on the difference in degradation efficiency between each cytokine and OPG. In addition, elucidation of the N-terminal amino acid sequences of OPG fragments revealed that Kgp primarily cleaved OPG in its death domain homologous region, which might prevent dimer formation of OPG required for inhibition of receptor activator of nuclear factor κB ligand. Collectively, our results suggest that degradation of OPG by Kgp is a crucial event in the development of osteoclastogenesis and bone loss in periodontitis.

Anti-Markovnikov hydrophosphoroselenoylation of alkenes using phosphorodiselenoic acid esters leading to the formation of phosphonoselenoic acid esters.

Phosphorodiselenoic acid esters with a binaphthyl group were reacted with alkenes in the presence of Bu3SnH and AIBN to give phosphonoselenoic acid esters in moderate to good yields. The addition of a phosphoroselenoyl group to alkenes proceeded in an anti-Markovnikov fashion. The diastereoselectivity was improved by the introduction of substituents to 3,3'-positions of a binaphthyl group.

Sequential one-pot addition of excess aryl-Grignard reagents and electrophiles to O-alkyl thioformates.

The sequential addition of aromatic Grignard reagents to O-alkyl thioformates proceeded to completion within 30 s to give aryl benzylic sulfanes in good yields. This reaction may begin with the nucleophilic attack of the Grignard reagent onto the carbon atom of the O-alkyl thioformates, followed by the elimination of ROMgBr to generate aromatic thioaldehydes, which then react with a second molecule of the Grignard reagent at the sulfur atom to form arylsulfanyl benzylic Grignard reagents. To confirm the generation of aromatic thioaldehydes, the reaction between O-alkyl thioformates and phenyl Grignard reagent was carried out in the presence of cyclopentadiene. As a result, hetero-Diels-Alder adducts of the thioaldehyde and the diene were formed. The treatment of a mixture of the thioformate and phenyl Grignard reagent with iodine gave 1,2-bis(phenylsulfanyl)-1,2-diphenyl ethane as a product, which indicated the formation of arylsulfanyl benzylic Grignard reagents in the reaction mixture. When electrophiles were added to the Grignard reagents that were generated in situ, four-component coupling products, that is, O-alkyl thioformates, two molecules of Grignard reagents, and electrophiles, were obtained in moderate-to-good yields. The use of silyl chloride or allylic bromides gave the adducts within 5 min, whereas the reaction with benzylic halides required more than 30 min. The addition to carbonyl compounds was complete within 1 min and the use of lithium bromide as an additive enhanced the yields of the four-component coupling products. Finally, oxiranes and imines also participated in the coupling reaction.

Downregulation of carbonic anhydrase IX promotes Col10a1 expression in chondrocytes.

Carbonic anhydrase (CA) IX is a transmembrane isozyme of CAs that catalyzes reversible hydration of CO(2). While it is known that CA IX is distributed in human embryonic chondrocytes, its role in chondrocyte differentiation has not been reported. In the present study, we found that Car9 mRNA and CA IX were expressed in proliferating but not hypertrophic chondrocytes. Next, we examined the role of CA IX in the expression of marker genes of chondrocyte differentiation in vitro. Introduction of Car9 siRNA to mouse primary chondrocytes obtained from costal cartilage induced the mRNA expressions of Col10a1, the gene for type X collagen α-1 chain, and Epas1, the gene for hypoxia-responsible factor-2α (HIF-2α), both of which are known to be characteristically expressed in hypertrophic chondrocytes. On the other hand, forced expression of CA IX had no effect of the proliferation of chondrocytes or the transcription of Col10a1 and Epas1, while the transcription of Col2a1 and Acan were up-regulated. Although HIF-2α has been reported to be a potent activator of Col10a1 transcription, Epas1 siRNA did not suppress Car9 siRNA-induced increment in Col10a1 expression, indicating that down-regulation of CA IX induces the expression of Col10a1 in chondrocytes in a HIF-2α-independent manner. On the other hand, cellular cAMP content was lowered by Car9 siRNA. Furthermore, the expression of Col10a1 mRNA after Car9 silencing was augmented by an inhibitor of protein kinase A, and suppressed by an inhibitor for phosphodiesterase as well as a brominated analog of cAMP. While these results suggest a possible involvement of cAMP-dependent pathway, at least in part, in induction of Col10a1 expression by down-regulation of Car9, more detailed study is required to clarify the role of CA IX in regulation of Col10a1 expression in chondrocytes.

Diastereo- and regioselective addition of thioamide dianions to imines and aziridines: synthesis of N-thioacyl-1,2-diamines and N-thioacyl-1,3-diamines.

Addition reactions of thioamide dianions that were derived from N-arylmethyl thioamides to imines and aziridines were carried out. The reactions of imines gave the addition products of N-thioacyl-1,2-diamines in a highly diastereoselective manner in good-to-excellent yields. The diastereomeric purity of these N-thioacyl-1,2-diamines could be enriched by simple recrystallization. The reduction of N-thioacyl-1,2-diamines with LiAlH(4) gave their corresponding 1,2-diamines in moderate-to-good yields with retention of their stereochemistry. The oxidative-desulfurization/cyclization of an N-thioacyl-1,2-diamine in CuCl(2)/O(2) and I(2)/pyridine systems gave the cyclized product in moderate yield and the trans isomer was obtained as the sole product. On the other hand, a similar cyclization reaction with antiformin (aq. NaClO) as an oxidant gave the cis isomer as the major product. The reactions of N-tosylaziridines gave the addition products of N-thioacyl-1,3-diamines with low diastereoselectivity but high regioselectivity and in good-to-excellent yields. The use of AlMe(3) as an additive improved the efficiency and regioselectivity of the reaction. The stereochemistry of the obtained products was determined by X-ray diffraction.

Imidazo[1,5-a]pyridine-1-ylalkylalcohols: synthesis via intramolecular cyclization of N-thioacyl 1,2-aminoalcohols and their silyl ethers and molecular structures.

Iodine-mediated cyclization of N-thioacyl 1,2-aminoalcohols derived from aromatic aldehydes and ketones mainly produced bis(1-imidazo[1,5-a]pyridyl)arylmethanes, whereas the reaction of N-thioacyl 1,2-aminoalcohols derived from aliphatic aldehydes and N-thioacyl 1,2-aminoalcohols protected with a silyl group with iodine gave imidazo[1,5-a]pyridine-1-ylalkylalcohols as a major product.

Monocarboxylate transporter-1 is required for cell death in mouse chondrocytic ATDC5 cells exposed to interleukin-1beta via late phase activation of nuclear factor kappaB and expression of phagocyte-type NADPH oxidase.

Interleukin-1ß (IL-1ß) induces cell death in chondrocytes in a nitric oxide (NO)- and reactive oxygen species (ROS)-dependent manner. In this study, increased production of lactate was observed in IL-1ß-treated mouse chondrocytic ATDC5 cells prior to the onset of their death. IL-1ß-induced cell death in ATDC5 cells was suppressed by introducing an siRNA for monocarboxylate transporter-1 (MCT-1), a lactate transporter distributed in plasma and mitochondrial inner membranes. Mct-1 knockdown also prevented IL-1ß-induced expression of phagocyte-type NADPH oxidase (NOX-2), an enzyme specialized for production of ROS, whereas it did not have an effect on inducible NO synthase. Suppression of IL-1ß-induced cell death by Nox-2 siRNA indicated that NOX-2 is involved in cell death. Phosphorylation and degradation of inhibitor of κBα (IκBα) from 5 to 20 min after the addition of IL-1ß was not affected by Mct-1 siRNA. In addition, IκBα was slightly decreased after 12 h of incubation with IL-1ß, and the decrease was prominent after 36 h, whereas activation of p65/RelA was observed from 12 to 48 h after exposure to IL-1ß. These changes were not seen in Mct-1-silenced cells. Forced expression of IκBα super repressor as well as treatment with the IκB kinase inhibitor BAY 11-7082 suppressed NOX-2 expression. Furthermore, Mct-1 siRNA lowered the level of ROS generated after 15-h exposure to IL-1ß, whereas a ROS scavenger, N-acetylcysteine, suppressed both late phase degradation of IκBα and Nox-2 expression. These results suggest that MCT-1 contributes to NOX-2 expression via late phase activation of NF-κB in a ROS-dependent manner in ATDC5 cells exposed to IL-1ß.

Intramolecular cyclization of in situ generated adducts formed between thioamide dianions and thioformamides leading to generation of 5-amino-2-thiazolines and 5-aminothiazoles, and their fluorescence properties.

Reactions of thioamide dianions, derived from secondary N-arylmethyl thioamides using BuLi, with thioformamides followed by the addition of iodine to yield 5-amino-2-thiazolines are described. Treatment of the 5-amino-2-thiazolines with iodine leads to a highly efficient production of 5-aminothiazoles. When N,N-diarylthioformamides are employed in this process, fluorescent 5-N,N-diarylthiazoles are obtained.

Iodine-mediated cyclization of N-thioacyl-1-(2-pyridyl)-1,2-aminoalcohols and their subsequent condensation leading to the formation of novel bis(1-imidazo[1,5-a]pyridyl)arylmethanes.

The treatment of N-thioacyl-1-(2-pyridyl)-1,2-aminoalcohols with iodine and pyridine in THF at room temperature for 30 min leads to the formation of bis(1-imidazo[1,5-a]pyridyl)arylmethanes as green solids in good to high yields.