Enzymatic resolution of 2-substituted tetrahydroquinolines. Convenient approaches to tricyclic quinoxalinediones as potent NMDA-glycine antagonists

Two approaches leading to the enantiomerically pure tricyclic quinoxalinedione class of NMDA-glycine antagonists using enzymatic resolutions are described. An intermediate, racemic methyl 1,2,3,4-tetrahydroquinoline-2-carboxylate 3, was resolved to (S)-3 in 97% ee and 47% yield (E=67) using -chymotrypsin. In an improved method, hydrolysis of another intermediate, racemic methyl 1,2,3,4-tetrahydroquinoline-2-acetate 4, with Novozym^® 435 provided the desired (S)-4 in high enantioselectivity and yield (93% ee, 50%, E=94).     

Electro- and photochemical properties of a (mu-alkoxo)bis(mu-carboxylato)diruthenium complex having two tetraphenylporphinato zinc(II) moieties

The novel (mu-alkoxo)bis(mu-carboxylato)diruthenium complex K[Ru(2)(dhpta)(mu-O(2)C-p-ZnTPP)(2)] 3 was prepared by simple ligand substitution reaction. Strong antiferromagnetic interaction between two Ru(III) ions of 3 was observed with a coupling constant of -425 approximately -404 cm(-1). The cyclic voltammogram of 3 can be explained in terms of superposition of those of ZnTPP-p-CO(2)H and K[Ru(2)(dhpta)(mu-O(2)CPh)(2)] 2, indicating no significant electrochemical interaction. The large conproportionation constant estimated from the reduction potentials for Ru(III)Ru(III) and Ru(II)Ru(III) indicates great stability of the mixed-valence state. The mixed-valence species [Ru(II)Ru(III)(dhpta)(mu-O(2)C-p-ZnTPP)(2)](2-) 4 was prepared by controlled potential electrolysis. The electronic absorption spectrum of 4 was quite similar to that of [Ru(II)Ru(III)(dhpta)(mu-O(2)CCH(3))(2)](2-) which is a typical Class II complex. The fluorescence from the S(2) state of the ZnTPP unit of 3 was significantly (78%) quenched. The electron transfer from the ZnTPP unit to Ru(III) ions in 3 is a plausible mechanism, even though energy transfer could not be ruled out completely. The free energy change for electron transfer, Delta G(CS), was estimated to be ca.-1.1 eV, which is similar to typical values for the reorganization energy lambda in polar solvents. Hence, the electron transfer scheme is situated almost at the top of the Marcus parabola, enabling ultrafast electron transfer.     

Beta-1,3-glucan polysaccharide can act as a one-dimensional host to create novel silica nanofiber structures

We have demonstrated that the creation of novel silica nanofibers with a uniform diameter is possible by utilizing beta-1,3-glucan polysaccharide as a one-dimensional host for monoalkoxysilane; the finding establishes that beta-1,3-glucan can act not only as a novel one-dimensional host for metal alkoxide polycondensation but also as an interface between inorganic nanofibers and functional organic molecules.     

Structural and conformational studies on euphornin and related diterpenes

In addition to euphornin, three new toxic substances (euphornins A, B and C) have been isolated from the plant $\text{Euphorbia}$$\text{helioscopia}$ L., and their absolute stereostructures also been elucidated on the basis of their spectral data and some chemical evidence together with an X-ray crystallographic analysis of the p-bromobenzoate derived from euphornin. Furthermore, their conformations have also been discussed.     

Controlled Stability of the Triple‐Stranded Helical Structure of a β‐1,3‐Glucan with a Chromophoric Aromatic Moiety at a Peripheral Position

We synthesized a semiartificial β‐1,3‐glucan, curdlan with dialkylaniline groups (CUR‐DA), that bears chromophoric aromatic groups at its peripheral positions. Spectroscopic studies as well as microscopic observations indicate that CUR‐DA adopts a triple‐stranded helical structure in water‐ or methanol‐rich solutions of dimethyl sulfoxide (DMSO). This triple‐stranded helical structure exhibits high thermal stability and resistance to base, attributes that are similar to those of the triple‐stranded helical structure of native β‐1,3‐glucans such as schizophyllan. Moreover, we found that the stability of the triple‐stranded helical structure can be easily modulated by solvent composition and metal‐ion (Zn²⁺) binding. As β‐1,3‐glucan polysaccharides are known to serve as “polymeric” hosts, including certain DNA molecules, carbon nanotubes, and conjugated polymers, and complexation occurs only with the single‐stranded structure, this information is very useful for the creation of these attractive polymeric composites, the controlled release of DNA, and so on.     

Preparation of Transparent, Partially-Crystallized BaTiO3 Monolithic Xerogels by Sol-Gel Processing

Transparent, partially-crystallized nanostructured barium titanate (BaTiO3) monolithic xerogels (dried at 90°C) have been successfully synthesized via hydrolysis of Ba, Ti alkoxide precursor solutions in a concentration range of 1.0 mol/l with addition of water with a molar ratio of H2O/Ba 6.3. Transparent monolithic xerogels obtained from a precursor solution of 1.0 mol/l remained transparent even after firing at 500°C in oxygen, although the degree of their transparency was considerably decreased. Firing at temperatures above 500°C yielded translucent ceramics of BaTiO3, and ultimately, firing above 600°C resulted in normal opaque ceramic bodies. Those obtained from a more concentrated precursor solution of 1.2 mol/l were, on the other hand, still transparent after firing at 600°C in oxygen, and turned opaque at 700°C. The results demonstrate that the materials retained their transparency even after pyrolysis of organic compounds involving exothermic oxidation at temperatures in the range of 200 to 400°C. The densification behavior of transparent BaTiO3 monolithic xerogels obtained was found to be excellent; for example, those derived from a 1.0 mol/l precursor solution could be sintered to form monolithic BaTiO3 ceramics with a relative sintered density of about 94% and an average grain size of 1 m by firing at 1100°C for 2 h in oxygen.     

Regioselective hydroxylation of the xylyl linker in a diiron(III) complex having a carboxylate-rich ligand with H2O2

Reaction of a diiron(III) complex having a xylta4- ligand (N,N,N',N'-m-xylylenediamine tetraacetate) with H2O2 resulted in regioselective hydroxylation of the m-xylyl linker. The reaction mimics the self-hydroxylation of a phenylalanine side chain found for ribonucleotide reductase (R2-W48F/D84E).