Selective mono-alkylation and arylation of aromatic dihalides by palladium-catalyzed cross-coupling with the Grignard and organozinc reagents

Dibromobenzene, dibromothiophenes, dichloro- and dibromopyridine are highly selectively mono-alkylated and arylated with Grignard or organozinc reagents in the presence of palladium complexes as catalysts.     

Photochemical reactions of polymers containing thiocyanatoacetyl groups and dyeing the resulting polymer films

Poly(styrene-co-4-thiocyanatoacetylstyrene) and poly(4-acetylstyrene-co-4-thiocyanatoacetyl-styrene) were prepared and their photochemical reactions were studied in the solid state. It was found that the thiocyanatoacetyl groups were easily rearranged with the corresponding isothiocyanatoacetyl groups by ultraviolet (UV) irradiation and that the resulting isothiocyanatoacetyl groups underwent intramolecular cyclization when treated with triethylamine or ammonia to yield oxazole-2-thione moieties. The irradiated polymer films could be dyed selectively with cationic dyes in an appropriate dye bath because of the formation of anionic species by keto-enol tautomerization of oxazole-2-thione moieties in an alkaline state.     

Comparison of potassium ion preference of potassium-sensing oligonucleotides,PSO-1 and PSO-2, carrying the human and Oxytricha telomeric sequence,respectively

Human [G(3)(TTAG(3))(3)] and Oxytricha [G(4)(T(4)G(4))(3)] telomere model oligonucleotides, PSO-1 and PSO-2, bearing two fluorophores, 6-carboxyfluorescein (6-FAM) and 6-carboxytetramethylrhodamine (6-TAMRA) at their 5'- and 3'-termini, respectively, were synthesized. Both of them can form an intramolecular antiparallel tetraplex upon addition of K(+), and an enhanced fluorescence resonance energy transfer (FRET) was observed. PSO-1 showed a 43,000 times higher selectivity for K(+) against Na(+). Fluorometric and circular dichroism spectrophotometric studies revealed that this system is useful for the evaluation of the interaction of different telomeric repeat oligonucleotide sequences with metal ions.     

Condensed thienopyrimidines. IV. Synthesis and gastric antisecretory activity of 2,3-dihydro-5H-oxazolothienopyrimidine derivatives

2,3-Dihydro-5H-oxazolo[3,2-a]thieno[3,2-d]-(2a--d), [3,4-d]-(2e--h), and [2,3-d]pyrimidine derivatives (2i,j) were synthesized and evaluated for gastric antisecretory activity. These analogues (2) were prepared stepwise starting from formylthiophenecarbamates (4). The structure-activity relationships of these compounds are discussed.     

Generation, reactions, and kinetics of sterically congested triplet diphenylcarbenes. Effects of bromine groups.

A series of polybrominated diphenylcarbenes (DPCs) are generated by irradiation of the corresponding precursor diazomethanes, and their reactivities are investigated by means of low-temperature spectroscopies as well as laser flash photolysis. Triplet bis(2,4,6-tribromophenyl)carbene was shown to decay by undergoing dimerization and to have a half-life of 1 s in a degassed benzene solution at room temperature, some 6 orders of magnitude longer-lived than the parent DPC. Anomalous effects of para substituents on the stability of the triplet are noted. Thus, while the replacement of a 4-bromine group with a methyl group resulted in a sharp decrease in the lifetime, introduction of a tert-butyl group resulted in a dramatic increase in the lifetime; triplet bis(2,6-dibromo-4-tert-butylphenyl)carbene was shown to have a half-life of 16 s in solution at room temperature. Attempts to increase the stability of these polybrominated DPCs by buttressing effects of a m-bromine group and by the synergetic effect of bromine and methyl groups are also described.     

Studies on the thermal decomposition of phthalate esters: IX. Thermal decomposition of bis(2-ethylhexyl) phthalate

A flow apparatus equipped with a spray nozzle was developed for investigating the thermal decomposition of esters with high boiling points and viscosities. The thermal decomposition of bis(2-ethylhexyl) phthalate (BEHP), which is a typical plasticizer for poly(vinyl chloride) with a high boiling point and viscosity, was carried out by the use of the flow apparatus. The thermal decomposition products were analysed by gas chromatography and the kinetic parameters were calculated. The kinetic parameter of bis(2-ethylhexyl) phthalate was k_BEHP (s^?1)=4.59·10¹¹ exp(?40600/RT). From a comparison with the values for phthalic esters, it is proposed that a cis-elimination reaction takes place with a two-step mechanism in which the rate-determining step is α-carbon cleavage.     

Conformational studies of multichain copoly(α-amino acids)s in solution

The conformational transition of multichain copoly(-amino acid)s consisting of copoly(-methyl-L-glutamyl-L-lysine) as backbone molecule and poly(-benzyl-L-glutamate) as branch molecules was studied in chloroform and DCA mixtures. The helix stability of backbone molecule is strongly affected by the length of branch molecules. In the case of the multichain copolymer having short branch molecular chains, i.e.,DP _br <10, the helix conformation of the backbone molecule is strictly affected by some interferences among the randomly coiled molecular chains. In the case of water-soluble multichain copolymer having poly(L-glutamic acid) or poly(L-lysine) as branch molecules, the transitional process from coil to helix is observed by depressing hydrostatic repulsion among the ionized side chain of branch molecules. However, such conformational transition is depressed to a considerable extent by interferences among the branch molecules.Abbreviations used (shown alphabetically) A/I molar ratio of NCA to initiator - Cbz carbobenzyloxy - DCA dichloroacetic acid - DMF N,N-dimethylformamide - DP _br number-average degree of polymerization of branches of multichain copolymer - Fw _br weight fraction of-benzyl-L-glutamyl residues of multichain copolymer - Mn number-average molecular weight - NCA N-carboxy anhydride of-amino acid - ORD optical rotatory dispersion     

Alkali metal-mediated proline aggregation in solution observed by coldspray ionization mass spectrometry

L-Proline aggregates to form cyclic clusters in the presence of alkali metal ions in solution, whereas a large-scale-aggregated chain structure was observed for several other amino acids. The major cyclic clusters are suggested to be constructed from trimeric and tetrameric subunits on the basis of direct solution analysis by coldspray ionization mass spectrometry.     

Photobleaching of bacteriorhodopsin solubilized with triton X-100

In the current studies, we examined the effects of hexagonal lattice formation with lipid membranes on the structural stability of native bacteriorhodopsin (bR). Denaturation kinetic measurements for bR solubilized with the mild nonionic detergent Triton X-100 (TX100) were performed in the dark and under illumination by visible light. The solubilized bR was stable in the dark over a wide concentration range of TX100 (1 to 200 mM). In purple membranes, a bilobed band was observed in visible circular dichroism spectra due to interactions between neighboring chromophores. At all concentrations of TX100, this was replaced by a single positive band. Upon illumination with visible light, TX100-solubilized bR clearly showed photobleaching to bacterioopsin. These experimental results suggest that photobleaching is due to a lack of intermolecular interactions inside the purple membrane lattice. Extensive kinetic measurements further revealed that the rate constant of photobleaching is strongly dependent on the detergent concentration, although the activation energy for photobleaching does not significantly change with the TX100 concentration. The mechanism of photobleaching for the solubilized bR is discussed with respect to detergent micelle properties.