Novel aggregation of [Ni(thiolato)2(amine)2]-type square planes assisted by silver(I) ions

Treatment of [Ni(L)][L =((-)SCH(2)CH(2)NH[double bond, length as m-dash]C(CH(3))-)(2)] with Ag(+) in water gave a pinwheel-like S-bridged Ni(II)(3)Ag(I)(2) structure in [Ag(2)[Ni(L)](3)](2+), which further reacted with [Ni(L)] to produce a Ni(II)(4)Ag(I)(2) structure in [Ag(2)[Ni(L)](4)](2+) and a Ni(II)(7)Ag(I)(4) structure in [Ag(4)[Ni(L)](7)](4+).     

NMR assignment methods for the aromatic ring resonances of phenylalanine and tyrosine residues in proteins

The unambiguous assignment of the aromatic ring resonances in proteins has been severely hampered by the inherently poor sensitivities of the currently available methodologies developed for uniformly 13C/15N-labeled proteins. Especially, the small chemical shift differences between aromatic ring carbons and protons for phenylalanine residues in proteins have prevented the selective observation and unambiguous assignment of each signal. We have solved all of the difficulties due to the tightly coupled spin systems by preparing regio-/stereoselectively 13C/2H/15N-labeled phenylalanine (Phe) and tyrosine (Tyr) to avoid the presence of directly connected 13C-1H pairs in the aromatic rings. The superiority of the new labeling schemes for the assignment of aromatic ring signals is clearly demonstrated for a 17 kDa calcium binding protein, calmodulin.     

Cyanobenzoylation and hydrocyanation of aldehydes with benzoyl cyanide using no catalyst

[reaction: see text] In the presence of MS 4A in DMSO, cyanobenzoylation of various aldehydes with benzoyl cyanide proceeded very smoothly to give the corresponding cyanohydrin benzoates in high to excellent yields without an acid or a base. On the other hand, reaction of aldehydes with BzCN in DMSO-H(2)O also occurred readily to afford the corresponding free cyanohydrins exclusively.     

Diastereoselective imino-aldol condensation of chiral 3-(p-Tolylsulfinyl)-2-furaldimine and ester enolates

(Ss)-3-(p-Tolylsufinyl)-2-furaldimine was synthesized, and condensation of the chiral furaldimine with lithium ester enolates has been examined. The product distribution of the reaction is dependent upon reaction conditions and on the kind of the substituent placed on the esters. Disubstituted ester enolate resulted in the exclusive formation of (4R)-beta-lactam, while unsubstituted, tert-butyl ester enolate preferentially gave (3R)-beta-amino ester. With the monosubstituted ester enolates, the condensation afforded (4R)-beta-lactams and/or (3R)-beta-amino esters as major products. This method has been applied to an efficient route to chiral furyl beta-lactams.     

Kinetics of γ-ray polymerization of formaldehyde in the presence of carbon dioxide

A kinetic study of the γ-ray polymerization of formaldehyde in toluene solution in the presence of carbon dioxide was carried out at temperatures of + 13 to ?17°C. Two modes of the polymerization, spontaneous and γ-ray polymerization, occur in this system. The γ-ray polymerization, experimentally separated from the spontaneous polymerization, was investigated. The rate of γ-ray polymerization increased slightly with the square root of carbon dioxide concentration. The rate of polymerization was also found to be proportional to the dose rate and the square of monomer concentration. The molecular weight of polymer formed was independent of the reaction condition. The apparent activation energy was estimated to be 10.3 kcal./mole. The kinetics of the γ-ray polymerization in the presence of carbon dioxide are explained quantitatively by a cationic mechanism, and the role of carbon dioxide is as an action of retardation for neutralization of the cationic initiating species, which was produced by γ-radiation, by means of a reverse reaction with an electron. Physical and mechanical properties of the polymer obtained by γ-ray polymerization were also investigated.     

Asymmetric crystallization of bisguanidinobenzene derivatives

We show that the mono-N-methylated and -ethylated derivatives of the achiral compound bisguanidinobenzene undergo spontaneous asymmetric crystallization into a chiral form with chiral space group P2₁2₁2₁. The absolute configurations of the chiral crystals were determined by X-ray crystallography and correlated with circular dichroism (CD) spectra recorded in the solid state. The corresponding protonated and isopropylated derivatives, by contrast, afforded achiral crystals.     

Synthesis and spectroscopic analysis of tetraphenylporphyrinatoantimony(V) complexes linked to boron-dipyrrin chromophore on axial ligands

Tetraphenylporphyrinatoantimony(V) complexes, linked to boron-dipyrrin chromophores on axial ligands, were synthesized. The fluorescence spectra of 1a, 1b and 1c (3-[4-(N,N′-difluorobornyl-5-dipyrrinyl)phenyl]propoxo(methoxo)antimony(V) tetraphenylporphyrin bromide (1a); 6-[4-(N,N′-difluorobornyl-5-dipyrrinyl)phenyl]hexyloxo(methoxo)antimony(V) tetraphenylporphyrin bromide (1b); bis{3-[4-(N,N′-difluorobornyl-5-dipyrrinyl)phenyl]propoxo}antimony(V) tetraphenylporphyrin bromide (1c)) were analyzed under the excitations of N,N′-difluorobornyl-5-dipyrrinylphenyl (Bdpy) and tetraphenylporphyrinatoantimony(V) (Sb(TPP)) chromophores. Under the irradiation of Bdpy chromophore, the excitation energy was transferred from Bdpy chromophore to the Sb(TPP) moiety at 0.13–0.40 of the quantum yields, even in a polar solvent. On the other hand, the emission of Sb(TPP) chromophores was quenched by Bdpy chromophores at rate constants of 10⁸–10⁹ s⁻¹, independent of on the solvent polarity. Under the excitation of the Bdpy chromophore of 1d (3-[4-(N,N′-difluorobornyl-5-dipyrrinyl)phenyl]propoxo(phenyloxo)antimony(V) tetraphenylporphyrin bromide) involving both the Bdpy and the phenoxy chromophores on the axial ligands, the excited singlet state of the Sb(TPP) chromophore generated by the energy transfer from the Bdpy chromophore was quenched by the phenoxy ligand via non-radiative processes involving electron transfer. However, rapid back electron-transfer may occur because no absorption of the anion radical of Sb(TPP) was observed by nanosecond laser photolysis.     

Enantioselective formation of a dynamic hydrogen-bonded assembly based on the chiral memory concept

In this paper, we report the enantioselective formation of a dynamic noncovalent double rosette assembly 1a(3).(CYA)(6) composed of three 2-pyridylcalix[4]arene dimelamines (1a) and six butylcyanuric acid molecules (BuCYA). The six 2-pyridyl functionalities of the assembly interact stereoselectively with chiral dicarboxylic acids 3a-e via two-point hydrogen-bonding interactions. One of the two enantiomeric assemblies (P- or M-) 1a(3).(CYA)(6) is formed in excess as the result of the complexation of the chiral diacids, resulting in formation of optically active assemblies. The complexations with dibenzoly tartaric acids D-3a and L-3a (3 equivalent), respectively, leading to the formation of diastereomeric assemblies (P)-1a(3).(BuCYA)(6).(D-3a)(3) and (M)-1a(3).(BuCYA)(6).(L-3a)(3) with 90% diastereomeric excess. The diastereomeric excess in (M)-1a(3).(BuCYA)(6).(L-3a)(3) is "memorized" when L-3a is removed by precipitation with ethlylenediamine (EDA). The assembly (M)-1a(3).(BuCYA)(6) is still optically active (90% enantiomeric excess), although none of its individual components are chiral. (M)-1a(3).(BuCYA)(6) has a high kinetic stability toward racemization (E(a) = 119 kJ mol(-)(1), half-life of (M)-1a(3).(BuCYA)(6) is ca. 1 week at 20 degrees C).     

Efficient algorithms for solving rank two and rank three bilinear programming problems

Finitely convergent algorithms for solving rank two and three bilinear programming problems are proposed. A rank k bilinear programming problem is a nonconvex quadratic programming problem with the following structure: % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4baFfea0dXde9vqpa0lb9% cq0dXdb9IqFHe9FjuP0-iq0dXdbba9pe0lb9hs0dXda91qaq-xfr-x% fj-hmeGabaqaciGacaGaaeqabaWaaeaaeaaakeaaieaacaWFTbGaa8% xAaiaa-5gacaWFPbGaa8xBaiaa-LgacaWF6bGaa8xzaiaa-bcacaWF% 7bacbiGaa43yamaaDaaaleaacaGFWaaabaGaa4hDaaaakiaa+Hhaca% GFRaGaa4hzamaaDaaaleaacaGFWaaabaGaa4hDaaaakiaa+LhacaGF% RaWaaabuaeaacaGFJbWaa0baaSqaaiaa+PgaaeaacaGF0baaaOGaam% iEaiabl+y6NjaadsgadaqhaaWcbaGaamOAaaqaaiaadshaaaGccaWG% 5bGaaiiFaaWcbaGaa8NAaiaa-1dacaWFXaaabeqdcqGHris5aOGaa4% hEaiabgIGiolaa+HfacaGFSaGaa4xEaiabgIGiolaa+LfacaWF9bGa% a8hlaaaa!5D2E!\[minimize \{ c_0^t x + d_0^t y + \sum\limits_{j = 1} {c_j^t xd_j^t y|} x \in X,y \in Y\} ,\]where X Rⁿ¹ and Y R ⁿ² are non-empty and bounded polytopes. We show that a variant of parametric simplex algorithm can solve large scale rank two bilinear programming problems efficiently. Also, we show that a cutting-cake algorithm, a more elaborate variant of parametric simplex algorithm can solve medium scale rank three problems.This research was supported in part by Grant-in-Aid for Scientific Research of the Ministry of Education, Science and Culture, Grant No. 63490010.     

Concise synthesis of anti-HIV-1 active (+)-inophyllum B and (+)-calanolide A by application of (-)-quinine-catalyzed intramolecular oxo-Michael addition

(-)-Quinine-catalyzed intramolecular oxo-Michael addition (IMA) of 7-hydroxy-5-methoxy-8-tigloylcoumarins was developed for the enantioselective construction of 2,3-dimethyl-4-chromanone systems in the context of the asymmetric synthesis of anti-HIV-1 active Calophyllum coumarins. Combination of the IMA and MgI(2)-assisted demethylation of the 5-methoxy group along with isomerization of the formed chromanone systems as key steps successfully led to the concise synthesis of (+)-inophyllum B and (+)-calanolide A, possible candidates for AIDS drugs. Further examination of the asymmetric IMA with cinchona alkaloids lacking a methoxy group on the quinoline skeleton suggested the influence of the methoxy substituent on stereoselectivity at the stereogenic centers of the chromanone systems.