Antioxidant effects of hydroxybenzalacetones on peroxynitrite-induced lipid peroxidation in red blood cell membrane ghost and SOS response in Salmonella typhimurium TA4107/pSK1002

Antioxidant activity of a series of hydroxybenzalacetones was determined against peroxynitrite-induced lipid peroxidation in red blood cell membrane and SOS response through DNA damage in bacterial cells. Hydroxybenzalacetone derivatives with hydroxy, methoxy, ethoxy or methyl substitution were analyzed and found to be more effective than the water-soluble vitamin E analogue Trolox. The inhibitory effect against lipid peroxidation correlated well to that against the SOS response, which is dependent on decomposition of peroxynitrite by hydroxybenzalacetones outside of the cell membrane. The antioxidant activity was shown to correlate well with the electric parameter sigma+. Electron-donating substituents with more negative sigma+ values increased the potencies. The result suggests that hydroxybenzalacetones with more electron-donating substituents will protect tissue more effectively against oxidative stress.     

Chiral β-dimethylaminoalkylphosphines. Highly efficient ligands for a nickel complex catalyzed asymmetric grignard cross-coupling reaction

Chiral β-dimethylaminoalkylphosphines were prepared starting with amino acids, (S)-alanine, (S)-phenylalanine, (R)-phenylglycine, (S)-valine, and (R)-tert-leucine. The chiral phosphines were found to be highly efficient ligands for a nickel catalyzed asymmetric Grignard cross-coupling reaction (38～94% optical yield).     

Efficient synthesis of 2-modified 1alpha,25-dihydroxy-19-norvitamin D3 with Julia olefination: high potency in induction of differentiation on HL-60 cells

Six novel 2-substituted analogues of 1alpha,25-dihydroxy-19-norvitamin D(3), 6a,b-8a,b, were efficiently synthesized utilizing (-)-quinic acid as the A-ring precursor. The C2-modified A-rings were prepared as 4-alkylated (3R,5R)-3,5-dihydroxycyclohexanones 12-15 from (-)-quinic acid based on radical allylation at the C4 position of methyl (-)-quinicate. The new type of the CD-ring coupling partner 23 was synthesized from 25-hydroxy Grundmann's ketone 19 to apply to the modified Julia olefination to construct a diene unit between the A-ring and the CD-ring. The coupling yields, including a deprotection step, were 47-62%. After the separation of the diastereomers based on C2 stereochemistry, the structure (2alpha or 2beta) was determined by (1)H NMR experiments and compared to DeLuca's 2-methyl- and 2-ethyl-1alpha,25-dihydroxy-19-norvitamin D(3). Thus, the synthesized 2alpha-(3-hydroxypropyl)-1alpha,25-dihydroxy-19-norvitamin D(3) (8a) showed almost the same potency in binding to the bovine thymus vitamin D receptor (VDR) as the natural hormone 1, while its beta-isomer 8b had only a 3% affinity. Both 2alpha-allyl- and 2alpha-propyl-1alpha,25-dihydroxy-19-norvitamin D(3) (6a and 7a) and their 2beta-analogues (6b and 7b) possessed a weak affinity for the VDR. The strong VDR ligand 8a was ca. 36-fold more potent in induction of HL-60 cell differentiation than 1, and interestingly, even the weaker ligand 8b showed a 6.7-fold higher potency in the cell differentiation activity than that of 1.     

Conformationally controlled (entropy effects), stereoselective vibrational quenching of singlet oxygen in the oxidative cleavage of oxazolidinone-functionalized enecarbamates through solvent and temperature variations

On photooxygenation (methylene blue as sensitizer) of E/Z enecarbamates, equipped with the oxazolidinone chiral auxiliary, the oxidative cleavage of the alkenyl functionality releases the enantiomerically enriched methyldesoxybenzoin (MDB) product. The extent (% ee) as well as the sense (R vs S) of the stereoselectivity in the MDB formation depends on the choice of the alkene configuration; the efficacy of stereocontrol may be tuned by appropriate solvent and temperature conditions. Highlighted is the finding that the formation of the preferred MDB enantiomer (R or S) depends for the E isomer on the chosen solvent and temperature, but not for the corresponding Z isomer. The activation parameters for the various solvents disclose that differential entropy effects (ΔΔS^‡) dominate the conformationally more flexible E diastereomers. As mechanistic rationale for this unprecedented conformationally imposed stereochemical behavior, we propose the competitive action of stereoselective vibrational quenching of the attacking singlet oxygen by the enecarbamate versus sterically controlled stereoselective oxidative cleavage of its double bond.     

Extraction behaviour of copper(II) and silver(I) with a thiacrown ether carboxylic acid, 2-(3,6,10,13-tetrathiacyclotetradec-1-oxy)hexanoic acid

The extraction behaviour of copper(II) and silver(I) with 2-(3,6,10,13-tetrathiacyclotetradec-1-oxy)hexanoic acid (TTCTOHA) was investigated at 25+/-0.1 degrees C and ionic strength of 0.1. The value of the logarithmic distribution coefficient, logK(DR) of TTCTOHA between octan-1-ol and aqueous phases was determined to be 4.13. Copper(II) was extracted with TTCTOHA into octan-1-ol as CuL(2), where L represents the anionic species of TTCTOHA. The logarithmic extraction constant, logK(ex(10)), was determined at -7.42. Silver(I) was extracted with TTCTOHA into octan-1-ol as AgL and Ag(2)L(2). The logarithmic distribution constant, logK(DC), of AgL was estimated to be 0.49. On the other hand, silver(I) was extracted into 1,2-dichloroethane as AgL and the logarithmic extraction constant, logK(ex(10)), was determined to be -2.24.     

Progress toward the total synthesis of ciguatoxins: a convergent synthesis of the FGHIJKLM ring fragment

[structure: see text] A highly convergent synthetic route to the FGHIJKLM ring fragment of ciguatoxins has been developed, which relied on extensive use of the B-alkyl Suzuki-Miyaura coupling reaction.     

A new method for the evaluation of the relative stability of organosulfur radicals by competitive elimination technique

The relative stability of various organosulfur radicals is estimated by competitive elimination technique using tributyltin radical and acetophenone derivatives having two different sulfur substituents at α and α positions.     

Syntheses and biological activities of renin inhibitors containing statine analogues

Syntheses and biological activities of dipeptide renin inhibitors that contain statine analogues are described. The key steps of the synthetic approach to dipeptide renin inhibitors are the asymmetric synthesis of 2(R)-substituted-3-aminocarbonylpropionic acids and the diastereoselective syntheses of (3S,4S)-statine analogues. These inhibitors (2,14-40) inhibited human renin in the 3-140 nM range. Inhibitor ES 6864 (2) was found to be a highly potent inhibitor of human renin (IC50: 4.6 x 10(-9) M) and showed high enzyme specificity. Oral administration of ES 6864 at 3 mg/kg to conscious, sodium-depleted marmosets inhibited plasma renin activity (PRA) more than 80% after 1 h.     

Triplet-mediated coupling of 5-bromo-1,3-dimetrhyluracil to Nb-methoxycarbonyltryptamine involving a double electron transfer

On acetone-sensitization, 5-bromo-1,3-dimethyluracil ($\text{1}$ reacts with N^b-methoxycarbonyltryptamine ($\text{4}$ under the assistance of an electron carrier such as 2-methoxynaphthalene to give a coupling product $\text{6}$. A mechanism involving a double electron transfer via the triplet state of $\text{1}$ is proposed.     

Photochemically generated silicon-carbon double-bonded intermediates VIII. Photolysis of phenyldisilane derivatives in the presence of olefins

Photolysis of phenylpentamethyldisilane, 1,1-diphenyltetramethyldisilane and 1-isopropyl-1-phenyltetramethyldisilane in the presence of a wide variety of olefins has been studied. All reactions investigated, with the exception of those with 1-methylcyclohexene and tetramethylethylene, afforded the corresponding 1/1 addition products. Yields of the adducts depended highly on the structure of the olefins used. In the photolysis of phenylpentamethyldisilane in the presence of an equimolar mixture of 1,1- and 1,2-bis(trimethylsilyl)ethene under competitive reaction conditions, the main product was the one arising from the 1,1-isomer. A possible mechanism for the process of addition of olefin to the photochemically generated silicon-carbon double-bonded intermediate (A) is discussed.