An approach to a chiral cycloalkanone-mediated asymmetric epoxidation of stilbene with oxone. (73/1302)

Chiral and C2-symmetric seven-membered cycloalkanones 2--6 bearing 1,2-diphenylethane-1,2-diamine and cyclohexane-1,2-diamine backbones were synthesized and evaluated their asymmetry inductive behaviours in an asymmetric epoxidation of stilbene with oxone. Although the reaction of the ketones 2 and 3 of a 1,2-diphenylethane-1,2-diamine backbone gave stilbene oxide in trace to 31% yield, those of the ketones 4-6 of a cyclohexane-1,2-diamine backbone gave the epoxide in satisfactorily high yield up to 98%. It is noteworthy that both reactions with use of stoichiometric and substoichiometric amounts of a ketone 4 gave the epoxide in the essentially same enantioselectivity, 17 and 18%. Eleven-membered cyclic ketones 7 and 8 bearing a binaphthalene backbone were also synthesized and examined their behaviours, while the enantioselectivity turned out to be marginal.  (+info)

Structure-dependent reactivity of oxyfunctionalized acetophenones in the photooxidation of DNA: base oxidation and strand breaks through photolytic radical formation (spin trapping, EPR spectroscopy, transient kinetics) versus photosensitization (electron transfer, hydrogen-atom abstraction). (74/1302)

The photooxidative damage of DNA, specifically guanine oxidation and strand-break formation, by sidechain-oxyfunctionalized acetophenones (hydroxy, methoxy, tert-butoxy and acetoxy derivatives), has been examined. The involvement of triplet-excited ketones and their reactivity towards DNA has been determined by time-resolved laser-flash spectroscopy. The generation of carbon-centered radical species upon Norrish-type I cleavage has been assessed by spin-trapping experiments with 5,5-dimethyl-1-pyrroline N-oxide, coupled with electron paramagnetic resonance spectroscopy. The observed DNA-base oxidation and strand-break formation is discussed in terms of the peroxyl radicals derived from the triplet-excited ketones by alpha cleavage and molecular oxygen trapping, as well as direct interaction of the excited states by electron transfer and hydrogen-atom abstraction. It is concluded that acetophenone derivatives, which produce radicals upon photolysis, in particular the hydroxy (AP-OH) and tert-butoxy (AP-O(t)Bu) derivatives, are more effective in oxidizing DNA.  (+info)

Membrane-bound quinoprotein D-arabitol dehydrogenase of Gluconobacter suboxydans IFO 3257: a versatile enzyme for the oxidative fermentation of various ketoses. (75/1302)

Solubilization of membrane-bound quinoprotein D-arabitol dehydrogenase (ARDH) was done successfully with the membrane fraction of Gluconobacter suboxydans IFO 3257. In enzyme solubilization and subsequent enzyme purification steps, special care was taken to purify ARDH as active as it was in the native membrane, after many disappointing trials. Selection of the best detergent, keeping ARDH as the holoenzyme by the addition of PQQ and Ca2+, and of a buffer system involving acetate buffer supplemented with Ca2+, were essential to treat the highly hydrophobic and thus labile enzyme. Purification of the enzyme was done by two steps of column chromatography on DEAE-Toyopearl and CM-Toyopearl in the presence of detergent and Ca2+. ARDH was homogenous and showed a single sedimentation peak in analytical ultracentrifugation. ARDH was dissociated into two different subunits upon SDS-PAGE with molecular masses of 82 kDa (subunit I) and 14 kDa (subunit II), forming a heterodimeric structure. ARDH was proven to be a quinoprotein by detecting a liberated PQQ from SDS-treated ARDH in HPLC chromatography. More preliminarily, an EDTA-treated membrane fraction lost the enzyme activity and ARDH activity was restored to the original level by the addition of PQQ and Ca2+. The most predominant unique character of ARDH, the substrate specificity, was highly versatile and many kinds of substrates were oxidized irreversibly by ARDH, not only pentitols but also other polyhydroxy alcohols including D-sorbitol, D-mannitol, glycerol, meso-erythritol, and 2,3-butanediol. ARDH may have its primary function in the oxidative fermentation of ketose production by acetic acid bacteria. ARDH contained no heme component, unlike the type II or type III quinoprotein alcohol dehydrogenase (ADH) and did not react with primary alcohols.  (+info)

A new antibiotic CJ-17,665 from Aspergillus ochraceus. (76/1302)

A new antibiotic, CJ-17,665 (I) was isolated from the fermentation broth of Aspergillus ochraceus, CL41582. It inhibits growth of multi-drug resistant Staphylococcus aureus, Streptococcus pyogenes, and Enterococcus faecalis, with MICs of 12.5, 12.5 and 25 microg/ml, respectively. The structure contains a diketopiperazine and an indole N-oxide moiety that is unusual in natural products.  (+info)

Ability of six different lipoprotein fractions to regulate the rate of hepatic cholesterogenesis in vivo. (77/1302)

Two in vivo assay procedures were used to study the inhibitory activity of cholesterol carried in three intestinal lymph and three serum lipoprotein fractions on the rate of cholesterol synthesis in the liver. In the first preparation, different lipoproteins were injected intravenously as a bolus into rats at the mid-light phase of the diurnal light cycle, following which they were killed 12 hours later in the mid-dark phase of the cycle. Using this assay, three intestinal lymph lipoprotein fractions of varying Sf values all produced a similar degree of inhibition which averaged approximately 11%/mg of cholesterol injected. The serum lipoprotein fractions caused only about one-third this amount of inhibition. Detailed analysis of events occurring within the liver during this 12-hour assay period revealed that there were marked differences in the rate of net cholesterol uptake into the liver and in the rate of new removal of cholesterol esters from the liver following injection of each of these different lipoprotein fractions. The amount of inhibition of sterol synthesis produced by any fraction was proportional to the product of the incremental increase in hepatic cholesterol ester content and the time over which this increase in esters occurred. In the second type of assay where the lipoprotein fractions were administered to the animals as a continuous intravenous infusion over 24 hours the largest increase in hepatic cholesterol ester content and the greatest inhibition of cholesterol synthesis was found with intestinal lipoproteins having Sf values larger than 8000. Intestinal lipoprotein fractions with lower Sf values and all serum lipoprotein fractions were significantly less effective in bringing about an increase in hepatic cholesterol ester content and in producing inhibition of cholesterol synthesis by the liver. These studies emphasize the primary role of cholesterol carried in lipoproteins of intestinal origin in regulating hepatic sterol synthesis. The inhibitory activity of these fractions appears to correlate with the ability of these lipoproteins to bring about a maximal increase in hepatic cholesterol ester content which, in turn, appears to relate to the capacity of these fractions to transfer cholesterol rapidly into the hepatocyte while, at the same time, slowing the rate of cholesterol mobilization from the liver.  (+info)

A cofactor approach to copper-dependent catalytic antibodies. (78/1302)

A strategy for the preparation of semisynthetic copper(II)-based catalytic metalloproteins is described in which a metal-binding bis-imidazole cofactor is incorporated into the combining site of the aldolase antibody 38C2. Antibody 38C2 features a large hydrophobic-combining site pocket with a highly nucleophilic lysine residue, Lys(H93), that can be covalently modified. A comparison of several lactone and anhydride reagents shows that the latter are the most effective and general derivatizing agents for the 38C2 Lys residue. A bis-imidazole anhydride (5) was efficiently prepared from N-methyl imidazole. The 38C2-5-Cu conjugate was prepared by either (i) initial derivatization of 38C2 with 5 followed by metallation with CuCl2, or (ii) precoordination of 5 with CuCl2 followed by conjugation with 38C2. The resulting 38C2-5-Cu conjugate was an active catalyst for the hydrolysis of the coordinating picolinate ester 11, following Michaelis-Menten kinetics [kcat(11) = 2.3 min(-1) and Km(11) 2.2 mM] with a rate enhancement [kcat(11)k(uncat)(11)] of 2.1 x 10(5). Comparison of the second-order rate constants of the modified 38C2 and the Cu(II)-bis-imidazolyl complex k(6-CuCl2) gives a rate enhancement of 3.5 x 10(4) in favor of the antibody complex with an effective molarity of 76.7 M, revealing a significant catalytic benefit to the binding of the bis-imidazolyl ligand into 38C2.  (+info)

The hepatitis C virus core protein interacts with NS5A and activates its caspase-mediated proteolytic cleavage. (79/1302)

Viral proteins interact with one another during viral replication, assembly, and maturation. Systematic interaction assays of the hepatitis C virus (HCV) proteins using the yeast two-hybrid method have uncovered a novel interaction between core and NS5A. This interaction was confirmed by in vitro binding assays, and coimmunoprecipitation in mammalian cells. Core and NS5A are also colocalized in COS-7 cells. Interestingly, NS5A is cleaved to give specific-size fragments, when core is coexpressed in mammalian cells. Overexpression of core produced many dying and rounded cells and effects such as DNA laddering and the truncation of poly(ADP-ribose) polymerase 1 (PARP1), both indicators of apoptosis. These observations led us to investigate the link between the induction of apoptosis by core and the cleavage of NS5A. The proteolysis of NS5A and these apoptotic events can be inhibited by caspase inhibitor, Z-VAD, indicating that core induces apoptosis and the cleavage of NS5A by caspases. In cells infected by the HCV, core may provide the intrinsic apoptotic signal, which produces truncated forms of NS5A. The biological function of core-NS5A interaction and the downstream effect of NS5A cleavage are discussed.  (+info)

Reductive metabolism of an alpha,beta-ketoalkyne, 4-phenyl-3-butyn-2-one, by rat liver preparations. (80/1302)

The reduction of the triple bond and carbonyl group of an alpha,beta-ketoalkyne, 4-phenyl-3-butyn-2-one (PBYO), by rat liver microsomes and cytosol was investigated. The triple-bond-reduced product trans-4-phenyl-3-buten-2-one (PBO) and the carbonyl-reduced product 4-phenyl-3-butyn-2-ol (PBYOL) were formed when PBYO was incubated with rat liver microsomes in the presence of NADPH. The triple bond of 1-phenyl-1-butyne, deprenyl, ethynylestradiol, ethinamate, and PBYOL, in which the triple bond is not adjacent to a carbonyl group, were not reduced by liver microsomes even in the presence of NADPH. PBO was further reduced to 4-phenyl-2-butanone (PBA) by liver cytosol with NADPH. PBYOL was also formed from PBYO by liver cytosol in the presence of NADPH or NADH. The microsomal triple-bond reductase activity was inhibited by disulfiram, 7-dehydrocholesterol, and 18 beta-glycyrrhetinic acid but not beta-diethylaminoethyldiphenylpropylacetate or carbon monoxide. The triple-bond reductase activity in liver microsomes was not enhanced by several inducers of the rat cytochrome P450 system. These results suggested that the triple-bond reduction is caused by a new type of reductase, not cytochrome P450. The microsomal and cytosolic carbonyl reductase activities were not inhibited by quercitrin, indomethacin, or phenobarbital. Only S-PBYOL was formed from PBYO by liver cytosol. In contrast, liver microsomes produced R-PBYOL together with the S-enantiomer to some extent. Ethoxyresorufin-O-dealkylase activity in rat liver microsomes was markedly inhibited by PBYO and PBO, partly by PBYOL, but not by PBA.  (+info)