Bifurcations of stationary solutions with triple junctions in phase separation problems — A new view of bifurcation analysis

Investigated here are bifurcations of stationary solutions with triple junctions to the curvature-driven motion of curves, which arises in phase separation problems. We demonstrate that, when seen from a new perspective, typical bifurcations under perturbations of domain shape can be analyzed using only elementary geometry.     

Polarographic studies on the catalytic wave of hydrogen with cobalt(II) sulphide

Summary Continuing the studies of catalytic hydrogen evolution on mercury cathodes, results are reported about the influence of cobalt(II) sulphide on the polarographic hydrogen wave in ammonia ammonium chloride buffer. The influence of the concentration of thioacetamide and of the kind of supporting electrolyte on polarograms and instantaneous current-time curves is discussed. Furthermore, the gas evolving from a mercury pool cathode by controlled potential electrolysis was detected and identified. A mechanism of the catalytic action of cobalt(II) sulphide is proposed.

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Zusammenfassung Als Fortsetzung von Arbeiten über die katalytische Wasserstoffabscheidung an Quecksilberkathoden wurde eine systematische Untersuchung über den Einfluß von Kobalt(II)-sulfid auf die polarographische Wasserstoffstufe in Ammoniak-Ammoniumchlorid-Puffer angestellt. Der Einfluß der Konzentration des Fällungsmittels und der Zusammensetzung des Leitelektrolyten auf das Polarogramm und auf die Gestalt von Strom-Zeit-Kurven am Einzeltropfen wird ausführlich diskutiert. Das bei der potentiostatischen Elektrolyse an einer Quecksilberpool-Kathode entwickelte Gas wurde ebenfalls untersucht. Ein Mechanismus für die katalytische Wirkung des Kobalt(II)-sulfids wird vorgeschlagen.

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Dedicated to Prof. Dr. M. von Stackelberg on his 70th birthday.     

Helix triangle: unique peptide-based molecular architecture

We here report a unique cyclic peptide structure, "helix triangle", as a unique example of peptide-based molecular architecture. The cyclic peptide is designed to have a triangular shape in which three 9mer helical peptide units make the sides and three pyrene derivatives make the apexes. The helical peptide units are ideally linear, and the pyrene units are ideal 60 degrees angular components. The yield of the cyclic peptide was relatively high despite its large cycle size. Absorption and fluorescence spectroscopy revealed that the three pyrene units do not interact with each other electronically, and circular dichroism spectroscopy indicated that the helical peptide units take 3(10)-helical conformation. Geometry optimization by the semi-empirical molecular orbital method gave a triangular structure with 3(10)-helices as the plausible molecular structure. To gain more information on the geometry and demonstrate one example of its self-assemblies, the monolayer of the cyclic peptide was prepared at the air/water interface, and its surface pressure-molecular area isotherm was studied. The isotherm indicated formation of a stable monolayer and suggested that the cyclic peptide actually takes the triangular structure predicted by the geometry optimization. The monolayer was then transferred onto a substrate and characterized by various methods. Ellipsometry and infrared reflection-absorption spectroscopy confirmed that the cyclic peptide has horizontal orientation to the surface in the monolayer. Furthermore, absorption and fluorescence spectroscopy showed that the isolated electronic properties of the pyrene units are intact even in a condensed state in the monolayer.     

Furopyridines. XX. Wittig-horner reaction of a phosphonate of reissert analogues of furo[3,2-c]-, -[2,3-c]- and -[3,2-b]pyridines

Furo[3,2-c]-( 1a ), -[2,3-c]- ( 1b ) and -[3,2-b]pyridine ( 1c ) were reacted with isopropyl chloroformate and trimethyl phosphite to give dimethyl 5-isopropoxycarbonyl-4,5-dihydrofuro[3,2-c]pyridine-4-phosphonate ( 2a ), dimethyl 6-isopropoxycarbonyl-6,7-dihydrofuro[2,3-c]pyridine-7-phosphonate ( 2b ) and dimethyl 4-isopropoxycarbonyl-4,7-dihydrofuro[3,2-b]pyridine-7-phosphonate ( 2c ) as unstable syrups. Reaction of 2b and 2c with n-butyllithium and then with benzaldehyde, p-methoxybenzaldehyde, p-cyanobenzalde-hyde or propionaldehyde afforded the normal Wittig reaction products 5b-H, 5b-OMe, 5b-CN, 5b-Et, 5c-H, 5c-H, 5c-OMe and 5c-CN , except for 2b with propionaldehyde. While, the same reactions of compound 2a and the reaction of 2b with propionaldehyde afforded the unexpected products, 5-isopropoxycar-bonylfuro[3,2-c]pyridinio-4-aryl-(or ethyl)methoxides 3a-H, 3a-OMe, 3a-CN and 3a-Et , 4-(1′-aryl(or ethyl)-1′-hydroxymethyl)furo[3,2-c]pyridines 4a-H, 4a-OMe, 4a-CN and 4a-Et accompanying formation of the normal products. Treatment of the normal Wittig reaction products with lithium diisopropylamide and then with acetone gave the derivatives alkylated at the 2-or the benzylic positions.     

Asymmetric total synthesis of (-)-Linderol A

The first asymmetric total synthesis of (-)-Linderol A, a potent inhibitor of melanin biosynthesis of cultured B-16 melanoma cells, has been achieved via two key reactions: a diastereoselective [2+2] photocycloaddition of a coumarin-3-carboxylate bearing a chiral auxiliary with 3-methyl-1-butene and a subsequent stereoconvergent transformation of the photoadducts with use of dimethylsulfoxonium methylide to afford a tetrahydrodibenzofuran derivative.     

First total synthesis of (+/-)-Linderol A,a tricyclic hexahydrodibenzofuran constituent of Lindera umbellata bark,with potent inhibitory activity on melanin biosynthesis of cultured B-16 melanoma cells

The first total synthesis of (+/-)-Linderol A, a hexahydrodibenzofuran constituent of Lindera umbellata bark, with potent inhibitory activity on the melanin biosynthesis of cultured B-16 melanoma cells, was achieved through 19 steps of reaction in 6.6% overall yield, in which the critical step was a tandem reaction of a 3-ethoxycarbonylcoumarin derivative with dimethylsulfoxonium methylide to yield the 2-ethoxycarbonylcyclopenta[b]benzofuran-3-ol derivative.     

Furopyridines. XXIV. Nitration,chlorination, acetoxylation and cyanation of 2,3-dihydrofuro[2,3-b]-, -[3,2-b]-, -[2,3-c]- and -[3,2-c]pyridine N-Oxides

Nitration of 2,3-dihydrofuro[3,2-b]- N-oxide 3b and -[2,3-c]pyridine N-oxide 3c afforded the nitropyridine compounds 4b, 5b and 6 from 3b and 4c, 5c, 5′c and 7 from 3c , while -[2,3-b]- N-oxide 3a and -[3,2-c]pyridine N-oxide 3d did not give the nitro compound. Chlorination of 3b and 3c with phosphorus oxychloride yielded mainly the chloropyridine derivatives 15b, 15′b from 3b and 15c and 15′c from 3c , whereas 3a and 3d gave pyridine derivatives formed through fission of the 1–2 ether bond of the furo-pyridines 13a , 14 and 13d . Acetoxylation of 3b and 3c gave 3-acetoxy derivatives 18b and 18c and the parent compound 1b and 1c . Acetoxylation of 3a yielded compounds formed through fission of the 1–2 bond 16 and 17 and 3d gave furopyridones 19 and 19 ′. Cyanation of 3b and 3c yielded mainly the cyanopyridine compounds 20b, 20c and 20′c . Cyanation of 3a and 3d gave the cyanopyridine compounds 20a , 20d and 20′d accompanying formation of the pyridine derivatives 21a, 21d and 21′d .     

Syntheses of 3-acetoacetylaminobenzo[b]furan derivatives having cysteinyl leukotriene 2 receptor antagonistic activity

Novel 3-acetoacetylaminobenzo[b]furan derivatives having a modified triene system at the 3-position were synthesized starting with 3-aminobenzo[b]furans. The enol isomers, 3-[(3-hydroxybut-2-enonyl)amino]benzo[b]furans (), of the 3-acetoacetylaminobenzo[b]furans were obtained as stable isomers owing to formation of a hydrogen bonding between the enol hydroxyl group and the amidocarbonyl group. The planarity of the C-2 substituent through the C-3 side chain suggested the existence of a modified conjugational triene system in the enol compound. Cysteinyl leukotriene 1 and 2 receptor antagonistic activities for these compounds were evaluated. 2-(4-Cyanobenzoyl or ethoxycarbonyl)-3-[(2-cyano-3-hydroxybut-2-enonyl)amino]benzo[b]furans (, ) were moderately active.     

Furopyridines. XII . Reaction of 3-bromo, 2-phenylthio and 2-phenylthio-3-bromo derivatives of furo[2,3-b]-, furo[3,2-b]-, furo[2,3-c]- and furo[3,2-c]pyridine with several alkyllithiums

This paper describes reactions of 3-bromo- 1a-d , 2-phenylthio- 5a-d and 2-phenylthio-3-bromofuropyridines 6a-d with n-butyl-, t-butyl- and methyllithium and lithioacetonitrile. Lithiation of compounds 1a-d with n-butyl- or methyllithium gave the parent furopyridines 2a-d and o-ethynylpyridinols 3a-d. Reaction of compounds 5a-d with methyllithium afforded o-(phenylthioethynyl)pyridinols 7a-d , which were also yielded by reaction of compounds 6a-d with t-butyl- or methyllithium. The phenylthio group in compounds 7a-d were substituted with t-butyl group by the reaction with excess t-butyllithium. In contrast, 2-phenylthio group in compounds 5a-d and 6a-d was substituted with cyanomethyl group by reaction with lithioacetonitrile to give compounds 11a-d and 10b, c respectively.