Cross-coupling of non-activated chloroalkanes with aryl Grignard reagents in the presence of iron/N-heterocyclic carbene catalysts

An efficient and high-yielding cross-coupling reaction of various primary, secondary, and tertiary alkyl chlorides with aryl Grignard reagents was achieved by using catalytic amounts of N-heterocyclic carbene ligands and iron salts. This reaction is a simple and efficient arylation method having applicability to a wide range of industrially abundant chloroalkanes, including polychloroalkanes, which are challenging substrates under conventional cross-coupling conditions.     

Stereospecific cross-coupling between alkenylboronates and alkyl halides catalyzed by iron-bisphosphine complexes

A stereospecific and high-yielding cross-coupling reaction between alkenylboron reagents and alkyl halides is described. The reaction has been achieved by using well-defined iron-bisphosphine complexes such as 1b FeCl(2)(3,5-t-Bu(2)-SciOPP), which was recently developed by the authors' group. Various nonactivated alkyl bromides and chlorides possessing a base/nucleophile-sensitive functional group can participate in the cross-coupling, demonstrating its utility for stereoselective synthesis of functional molecules bearing a carbon-carbon double bond.     

Origins of oxygen atoms in a marine ladder-frame polyether: evidence of monooxygenation by 18O-labeling and using tandem mass spectrometry

Yessotoxin is a ladder-frame polyether produced by the dinoflagellate Protoceratium reticulatum. Previous labeling experiments using (13)C-acetate established the unique assembly of the carbon chain from intact and cleaved acetate units. The origins of ether and hydroxy oxygens in the molecule, which would yield further information regarding the assembly of the ladder-frame structure, have yet to be established. In this study, we describe the incorporation of (18)O in one experiment where the dinoflagellate was cultured under (18)O(2) atmosphere and in a second where the culture media was supplemented with [(18)O(2)]acetate. Labeled yessotoxin obtained from these experiments was subjected to collision-induced dissociation tandem mass spectrometry to determine the positions of (18)O-incorporation pattern in the molecule. Detailed analyses of product ions from the fragmentation processes led to the identification of (18)O-labeled positions and the incorporation ratios. The data revealed that the ether oxygens were labeled from (18)O(2) and the hydroxy oxygen on C32 was derived from [(18)O(2)]acetate. These results support a proposed biosynthetic mechanism of marine ladder-frame polyethers that a polyene precursor was oxidized by a monooxygenase after acetate condensation.     

Cancer chemoprevention by carotenoids

Carotenoids are natural fat-soluble pigments that provide bright coloration to plants and animals. Dietary intake of carotenoids is inversely associated with the risk of a variety of cancers in different tissues. Preclinical studies have shown that some carotenoids have potent antitumor effects both in vitro and in vivo, suggesting potential preventive and/or therapeutic roles for the compounds. Since chemoprevention is one of the most important strategies in the control of cancer development, molecular mechanism-based cancer chemoprevention using carotenoids seems to be an attractive approach. Various carotenoids, such as β-carotene, a-carotene, lycopene, lutein, zeaxanthin, β-cryptoxanthin, fucoxanthin, canthaxanthin and astaxanthin, have been proven to have anti-carcinogenic activity in several tissues, although high doses of β-carotene failed to exhibit chemopreventive activity in clinical trials. In this review, cancer prevention using carotenoids are reviewed and the possible mechanisms of action are described.     

Polycationic gramicidin s analogues with both high antibiotic activity and very low hemolytic activity

The substitution of each constituent amino acid residue of gramicidin S (GS), cyclo(-Val(1,1')-Orn(2,2')-Leu(3,3')-D-Phe(4,4')-Pro(5,5')-)(2) with Lys residue indicated that each side chain structure of the constituent amino acid residues affect largely the antibiotic activity and hemolytic activity of GS. Further, the substitution of D-Phe(4,4') and Pro(5,5') residues with basic amino acid residues as a Lys residue results the high antibiotic activity and the very low hemolytic activity. Thus, we have found novel positions on the scaffold of GS at D-Phe(4,4') and Pro(5,5') residues whose modification will significantly increase the therapeutic index.     

Flow injection determination of trace amounts of copper based on its catalytic effect on the oxidation of 3, 3′, 5, 5′-tetramethylbenzidine by cumene hydroperoxide

A sensitive and selective flow-injection method has been developed for the catalytic determination of copper(II). The method is based on the oxidation of 3,3′,5,5′-tetramethylbenzidine by cumene hydroperoxide as an organic oxidant in an acidic medium. A highly sensitivity has been achieved by adding 2,9-dimethyl-1,10-phenanthroline as an activator and benzyldimethyltetradecylammonium chloride (zephiramine) as a surfactant. The reaction was spectrophotometrically monitored by measuring the increase in absorbance of oxidation product of 3,3′,5,5′-tetramethylbenzidine at 650 nm. The calibration curve was linear over the range of 0.5–3.0 ng mL^?1 at a rate of 30 samples h^?1. Most of the diverse ions did not interfere with the determination of copper up to at least 50-fold excess. The serious interference by iron(III) was eliminated by addition of fluoride. The method was successfully applied to the determination of copper in water samples.     

Blacklight-Induced Hydroxylation of Arylboronic Acids Leading to Hydroxyarenes Using Molecular Oxygen and Tetrabutylammonium Borohydride

A new simple protocol for the conversion of arylboronic acids to hydroxyarenes was achieved using molecular oxygen in the presence of tetrabutylammonium borohydride under blacklight irradiation (360 nm). A radical chain mechanism in which a superoxide ion (O₂^−.) plays a key role is proposed.