Cyclization-Carbonylation of 2-Alkynyl Primary Benzamides using p-Benzoquinone under Neutral Conditions.

A palladium-catalyzed cyclization-carbonylation of 2-alkynyl primary benzamides 1 afforded methyl 3-substituted 1-methoxyisoquinoline-4-carboxylates 6 in good to moderate yields. In the case of mesylate 1r, 12 was obtained directly via a cyclization-carbonylation-cyclization cascade. Compounds 6 were converted to isoquinolin-1(2H)-ones 8 in good yields under microwave irradiation. In the case of the mesylate 6q, tricyclic isoquinolinone 10 was obtained in good yield. The reactions of thiophene-2-carboxamide derivatives also proceeded well.

A sequential reaction of picolinamide with benzaldehydes promoted by Pd(TFA)2: rapid access to 4,5-disubstituted 2-(pyridin-2-yl)oxazoles in n-octane.

We developed a synthetic method for obtaining 4,5-disubstituted 2-(pyridin-2-yl)oxazoles from picolinamide and aldehydes by employing Pd(TFA)2 as the catalyst in n-octane. This cascade reaction involves the condensation of picolinamide and two aldehyde molecules promoted by trifluoroacetic acid (TFA) generated in situ from Pd(TFA)2. This one-pot protocol provides rapid access to synthetically valuable triaryloxazoles from readily available starting materials under mild conditions. An 18O labeling study revealed that this tandem reaction proceeded via a different reaction mechanism compared to the Robinson-Gabriel oxazole synthesis.

Daphnepedunins A-F, Anti-HIV Macrocyclic Daphnane Orthoester Diterpenoids from Daphne pedunculata.

From the whole plant of Daphne pedunculata, 12 macrocyclic daphnane diterpenoids, including six new compounds, daphnepedunins A-F (1-4, 9, and 10), were isolated. Their structures were elucidated by physiochemical and spectroscopic data analysis, the modified Mosher's method, and X-ray crystallography. The isolated compounds were evaluated for anti-HIV activity against HIV-1 infection in MT4 cells and showed significant anti-HIV activity with IC50 values of 36.3-994 nM. A consideration of the anti-HIV activity of these compounds provided further insight into the structure-activity relationships of macrocyclic daphnane diterpenoids.

Synthesis, crystal structure, and properties of methyl-substituted coronene amide analogue.

A coronene amide analogue was synthesized in six steps using an improved method at the final biarylation step. The key to the progress of palladium-mediated biarylation involved the introduction of three methyl groups to suppress the undesired reaction and the use of tri-tert-butylphosphine as the ligand for palladium. Single-crystal X-ray analysis revealed that the core unit of the coronene analogue has a non-planar structure.

Conformational Properties of Aromatic Amides Bearing Imidazole Ring and Acid-Induced Trans-Cis Amide Switching.

Aromatic amides bearing secondary amide bond exist in trans conformation both in the crystal and in solution, whereas the conformation of the N-methylated derivatives is cis in the crystal and predominantly cis in various solvents. The cis conformational preference of N-alkylated benzanilide provides access to aromatic foldamers such as oligo(N-alkyl-p-benzamide)s, which adopt dynamic helical structures. Here, the conformational properties of imidazole-substituted amide in the crystal and in solution were examined. Imidazole-substituted amides 2a and 4a existed mainly in the cis conformation in solution. The ratio of the cis conformer of N-methyl-N-(1-methyl-1H-imidazol-4-yl)benzamide (4a) was smaller than that of N,1-dimethyl-N-phenyl-1H-imidazole-2-carboxamide (2a) or N-methylbenzanilide, but the introduction of a substituent strongly affected the conformer ratio. Compounds 6a and 7a bearing an electron-withdrawing group on the imidazole ring existed predominantly in trans form. On the other hand, the introduction of an electron-withdrawing group on the phenyl ring or a bulky substituent on the amide nitrogen of 4a increased the ratio of cis conformer. Further, the major conformer of N-alkylated N-imidazolylamides was switched from cis to trans by the addition of acid. These results suggest that imidazole-substituted amides might be applicable as conformational switches in aromatic foldamers to enable environment-dependent structural change.

Synthesis of the Proposed Structure of Mohangic Acid C.

The proposed structure of mohangic acid C (3) was stereoselectively synthesized via a catalytic asymmetric aldol reaction to install a p-aminoacetophenone moiety, Marshall propargylation furnishing two stereocenters, and Cu-mediated Stille-type coupling to construct the whole framework of 3.

Dehydrative amination of benzhydrols with electron-withdrawing group-substituted 2-aminopyridines utilizing Au(III)/TPPMS catalyst system in water.

We report a method for gold(III)/sodium diphenylphosphinobenzene-3-sulfonate (TPPMS)-catalyzed direct amination of benzhydrols using 2-aminopyridines with poor nucleophilic character in water. Various functional groups such as electron-withdrawing nitro, cyano and halogen groups were tolerated well to form the desired N-benzylated 2-aminopyridine compounds. On the basis of mechanistic studies including kinetic profiles, Hammett study and isotope effects, we propose a pathway in which a Lewis acidic gold cation species activates the sp3 C-O bond of the alcohol in the rate-determining step.

Conformational Control of [2]Rotaxane by Hydrogen Bond.

A series of [2]rotaxanes with various functional groups in the axle component was synthesized by the oxidative dimerization of alkynes, which is mediated by a macrocyclic phenanthroline-Cu complex. The rotaxanes were fully characterized by spectroscopic methods, and the structure of a rotaxane was determined by X-ray crystallographic analysis. The interaction between the ring component and the axle component was studied in detail to understand the conformation of the rotaxanes. The presence of the hydrogen bond between the phenanthroline moiety in the macrocyclic component and the acidic proton in the axle component influenced the conformation of rotaxane.

Selective Synthesis of the Aminobutadiene Intermediate and Mechanistic Analysis of 1,4-Dihydropyridine Formation Reaction in Water.

We previously isolated an aminobutadiene derivative as a by-product in the synthesis of a 1,4-dihydropyridine (1,4-DHP) derivative by the reaction of methyl propiolate with excess ammonium acetate in water, and we proposed that it is an intermediate in the formation of 1,4-DHP. Here, to test this idea and to investigate the reaction mechanism, we selectively synthesized the aminobutadiene derivative in EtOH and examined its reactivity. The yield of the aminobutadiene derivative was increased in the presence of excess ammonium salt. X-Ray crystal structure analysis indicated the presence of an intramolecular hydrogen bond between the terminal amine and ester carbonyl oxygen, together with a short C-N bond length consistent with enamine-imine equilibrium. Direct cyclization of the aminobutadiene derivative with methyl propiolate to afford the 1,4-DHP derivative did not proceed well, but the yield was increased in the presence of morpholine salt as an additive. These results suggest that the predominant reaction pathway from the intermediate to 1,4-DHP in water involves Michael addition of a second amine molecule and reaction with methyl propiolate, followed by intramolecular cyclization and elimination of amine.

Discovery of remogliflozin etabonate: A potent and highly selective SGLT2 inhibitor.

We optimized the structure of an active metabolite (1) of WAY-123783, which was obtained from mouse urine after oral administration, to improve selectivity for SGLT2 and oral bioavailability. O-glucoside derivative 24 (remogliflozin etabonate) was subsequently identified as a potent, highly selective, and orally available SGLT2 inhibitor.

Construction of Aromatic Multilayered Structures Based on the Conformational Properties of N,N'-Dimethylated Squaramide.

Squaramide is a highly rigid four-membered ring system bearing two carbonyl and two amino groups, and its derivatives have found applications in many fields. We synthesized several N,N'-dimethylated oligosquaramides linked via phenyl groups, and investigated their structures in the crystalline state and in solution. Compounds 1, 2 (bissquaramides), and 13 (trissquaramide) exist as folded structures in the crystalline state, in which the aromatic rings are located in a face-to-face position. In their multilayered structures, the benzene rings are more nearly parallel and are closer to each other, compared with those in N,N'-dimethylated oligoureas. Individual molecules of meta-connected compounds 2 and 13 show a helical structure with all-R or all-S axis chirality, but afford only racemic crystals. The NMR spectra indicated that these compounds retain well-ordered folded structures in solution. The unique steric and electronic properties of N,N'-dimethylated squaramide can provide access to novel functional aromatic multilayered and helical foldamers.

Water-promoted dehydrative coupling of 2-aminopyridines in heptane via a borrowing hydrogen strategy.

A synthetic method for dehydrative N-benzylation promoted by water molecules in heptane using a π-benzylpalladium system has been developed. The presence of water significantly accelerates carbon-nitrogen bond formation, which is accomplished in an atom-economical process to afford the corresponding N-monobenzylated products. A crossover experiment afforded H/D scrambled products, which is consistent with a borrowing hydrogen mechanism. Kinetic isotope effect measurements revealed that benzylic carbon-hydrogen bond cleavage was the rate-determining step.

[Identification of Descarbonsildenafil in an Adulterated Dietary Supplement and Evaluation of Its Inhibitory Activity for Phosphodiesterase Type 5 (PDE5)].

Some illegal dietary supplements contain phosphodiesterase type 5 (PDE5) inhibitors, such as sildenafil, for exerting "therapeutic" effects in erectile dysfunction. This is apparently dangerous, and thus, should be appropriately regulated. Identification of descarbonsildenafil was first reported in Singapore in a coffee sample labeled to exert male sexual performance enhancement effects. However, it is unclear whether the compound possesses PDE5 inhibitory activity. We encountered during our survey of dietary supplements, a sexual enhancement product commercially available in Tokyo, in which a peak presumed to be of descarbonsildenafil was detected by LC-UV and electrospray ionization-tandem MS (ESI-MS/MS). The compound was isolated and identified as descarbonsildenafil with liquid chromatography-quadrupole time-of-flight-mass spectrometry (LC-QTOF-MS), NMR, and X-ray crystal structural analysis. In addition, descarbonsildenafil showed PDE5 inhibitory activity in PDE5 inhibition assay, and its IC50 value for PDE5A1 was found to be 30 nmol/L. The results of INADEQUATE NMR and X-ray crystal structural analysis in this study provide information for the identification of descarbonsildenafil. Since this study indicates that this compound is a PDE5 inhibitor having adequate activity, it is regulated as a drug component in Japan.

Development of Helical Aromatic Amide Foldamers with a Diphenylacetylene Backbone.

We designed and synthesized aromatic polyamides with a diphenylacetylene backbone, α-DPA and ß-DPA, bearing (S)-α- and (S)-ß-methyl-substituted triethyleneglycol (TEG) side chains, respectively, and examined their conformations in solution. Both polymers exhibit strong, solvent polarity-dependent circular dichroism spectra, which indicated that they take helical conformations in low-polarity solvents. The spectra were mirror images, depending on the chiral position of the side chains. Thus, the polyamide α-DPA bearing (S)-α-methyl-substituted TEG groups takes a left-handed helical conformation, while the polyamide ß-DPA with (S)-ß-methyl-substituted TEG groups takes a right-handed helical conformation. The difference in the screw sense of α-DPA and ß-DPA would be caused by the steric interaction between the main chain and the side chain, as observed in poly(p-benzamide) possessing (S)-ß-methyl-substituted TEG side chains (ß-PA) because the large cavity of the helical structure of DPA would disturb the solvophobically induced helical folding. Detailed conformational analyses of the oligoamides 6-12 with ß-methyl-substituted TEG groups were conducted. Theoretical calculations indicated that the oligoamides with ß-methyl-substituted TEG groups exist in a helical conformation with a cavity of 7 Å in diameter. The 1H NMR spectra of the oligomers revealed interactions with small anions such as chloride and acetate anions and with pyridinium cations.

Synthesis and Systematic Structural Analysis of Cationic Half-Sandwich Ruthenium Chalcogenocarbonyl Complexes.

Although the chemistry of transition-metal complexes with carbonyl (CO) and thiocarbonyl (CS) ligands has been well developed, their heavier analogues, namely selenocarbonyl (CSe) and tellurocarbonyl (CTe) complexes remain scarce. The limited availability of such CSe and CTe complexes has so far hampered our understanding of the differences between such chalcogenocarbonyl (CE: E=O, S, Se, Te) ligands. Herein, we report the synthesis and properties of a series of cationic half-sandwich ruthenium CE complexes of the type [CpRu(CE)(H2 IMes)(CNCH2 Ts)][BArF 4 ] (Cp=η5 -C5 H5 - ; H2 IMes=1,3-dimesitylimidazolin-2-ylidene; ArF =3,5-(CF3 )2 C6 H3 ). A combination of X-ray diffraction analyses, NMR spectroscopic analyses, and DFT calculations revealed an increasing π-accepting ability of the CE ligands in the order O

Cylindrical macrocyclic compounds synthesized by connecting two bowl-shaped calix[3]aramide moieties: structures and chiroptical properties.

Calix[3]aramide-based macrocycles 1 were successfully synthesized by a Glaser coupling reaction of two meta-calix[3]aramide moieties that have three ethynyl groups. The obtained macrocycles have stereoisomers: an enantiomeric pair and a meso form based on a combination of amide bond directions in the calix[3]aramide moieties at both ends of the molecule. Characteristic absorption spectra derived from the 1,4-diphenylbutadiyne structure were observed, while their ECD spectra were mirror-images. Single-crystal X-ray analysis revealed that each stereoisomer had a cylindrical rigid shape, and the absolute structure of the chiral-form was also assigned by comparing the Flack parameters. Mirror-image VCD spectra were observed for the enantiomeric chiral forms, and a VCD signal pattern of one enantiomer corresponded to that predicted by the relationship between the dihedral angle of the pair of C[double bond, length as m-dash]O groups.

Synthesis and chiroptical properties of cylindrical macrocycles comprising two calix[3]aramide moieties.

Calix[3]aramide-based cylindrical macrocycles were synthesized by the one-step amide coupling reaction of a monomer containing two meta-alkylaminobenzoic acid units linked by para-phenylene bridges. The major products included a meso-form and an enantiomeric pair, with stereochemistry derived from the direction of the amide bonds and their fixed conformation. Mirror-image ECD, VCD, and CPL spectra were observed in the enantiomeric pair and the absolute structure was determined by comparing measured and calculated ECD and VCD spectra.

Gold(III)-Catalyzed Decarboxylative C3-Benzylation of Indole-3-carboxylic Acids with Benzylic Alcohols in Water.

A strategy for the gold(III)-catalyzed decarboxylative coupling reaction of indole-3-carboxylic acids with benzylic alcohols has been developed. This cascade reaction is devised as a straightforward and efficient synthetic route for 3-benzylindoles in moderate to excellent yields (50-93%). A Hammett study of the protodecarboxylation gives a negative ρ value, suggesting that there is a buildup of positive charge on the indole ring in the transition state. Furthermore, comparison of initial rates in H2O and in D2O reveals an observed kinetic solvent isotope effect (KSIE = 2.7). This simple protocol, which affords the desired products with CO2 and water as the coproducts, can be achieved under mild conditions without the need for base or other additives in water.

Asymmetric Cyclizative Dimerization of (ortho-Alkynyl Phenyl) (Methoxymethyl) Sulfides with Palladium(II) Bisoxazoline Catalyst.

The first example of an asymmetric cyclization-dimerization of (ortho-alkynyl phenyl) (methoxymethyl) sulfides with a palladium(II) bisoxazoline (box) catalyst has been developed. The box ligand enhances the alkynophilicity of benzothienyl palladium(II) intermediate A and thus promotes coordination of the second alkyne substrate, leading to the dimerization. The characteristic properties of the box ligand were supported by density functional theory (DFT) calculations of the intermediate. Axially chiral bibenzothiophenes were obtained in good yields with good enantioselectivities.