Selective Propargylation of Carbonyl Compounds and Imines with Barium Reagents

A Barbier‐type regioselective propargylation of aldehydes and ketones with (3‐bromobut‐1‐ynyl)trimethylsilane has been achieved using reactive barium as a low‐valent metal in THF. Especially in the case of ketones, the corresponding homopropargylic alcohols form almost exclusively. In the reaction of α,β‐unsaturated carbonyl compounds, only 1,2‐adducts have been observed. This method is also applicable to propargylation of imines, and the corresponding homopropargylic amines are obtained regiospecifically in good yields with diastereomeric ratios of up to 87:13.     

Fibrinolytic effect of tissue plasminogen activator on cerebral embolism in stroke-prone spontaneously hypertensive rats.

To study the thrombolytic effect of tissue plasminogen activator (t-PA) on cerebral emboli, we characterized cerebral embolization in stroke-prone spontaneously hypertensive rats (SHRSPs) and Wistar Kyoto rats (WKYs). [125I]Fibrin clot particles (20-100 microns diameter) were injected twice at an interval of 90 min into the left internal carotid artery of WKYs and SHRSPs. After each injection, spontaneous embolus dissolution was monitored with a gamma-ray detector placed on the head of the embolic rats. Embolus dissolution was spontaneously generated in 15 min after the injection of fibrin clots. In WKYs, 21% and 42% of the clots were dissolved 30 and 90 min after the second embolization, respectively. On the other hand, the spontaneous embolus dissolution in SHRSPs was significantly lower than that of WKYs, indicating that the endogenous fibrinolytic ability of SHRSPs is less potent than that of normotensive rats. The intravenous administration of t-PA at doses of 75, 250 and 750 micrograms/kg caused a dose-dependent embolus dissolution in SHRSPs. Furthermore, systematically applied t-PA produced embolus dissolution without causing systemic plasminogen activation, fibrinogen breakdown or bleeding. In conclusion, the intravenous administration of t-PA produces selective embolus dissolution without systemic fibrino(geno)lysis in a cerebral embolic SHRSP.     

Asymmetric synthesis of axially chiral benzamides and anilides by enantiotopic lithiation of prochiral arene chromium complexes

Axially chiral benzamides and anilides were prepared by enantiotopic lithiation at the distinguished benzylic methyl of prochiral tricarbonylchromium complexes of N,N-diethyl 2,6-dimethylbenzamide (1) and N-methyl-N-acyl 2,6-dimethylaniline (14 and 21) with a chiral lithium amide base followed by electrophilic substitution in good yields with high optical purity. The resulting axially chiral chromium-complexed benzamides and anilides were oxidized under air to give chromium-free axially chiral benzamides and anilides in an enantiomerically active form without axial bond rotation at room temperature.     

Metal-assisted stabilization and probing of collagenous triple helices

Collagen model peptides that contain 2,2'-bipyridyl (bpy) ligands were designed and synthesized. The thermal stability of the collagenous triple helix was increased by forming an Fe(II)(bpy-peptide)(3) complex. The chirality of the metal center was shifted to form right-handed Delta-isomers induced by the supercoiling of the peptide moiety. Moreover, the refolding rate of the triple helix was increased in the presence of Fe(II). This metal-coordinating system possesses potential to be used to stabilize the triple-helical conformation as well as to probe the folding status of collagen model peptides.     

Enantiomeric separations of cationic and neutral compounds by capillary electrochromatography with monolithic chiral stationary phases of beta-cyclodextrin-bonded negatively charged polyacrylamide gels

Enantiomeric separation by capillary electrochromatography with beta-cyclodextrin-bonded negatively charged polyacrylamide gels was examined. The columns used are capillaries filled with a negatively charged polyacrylamide gel, a so-called monolithic stationary phase, to which allyl carbamoylated beta-CD (AC-beta-CD) derivatives covalently bind. The capillary wall is activated first with a bifunctional reagent to make the resulting gel bind covalently to the inner surface of the fused-silica tubing. Enantiomeric separations of 15 cationic compounds were achieved using the above-mentioned columns and mobile phases of 200 mmol l(-1) Tris-300 mmol I(-1) boric acid buffer (pH 7.0 or 9.0) or 200 mmol l(-1) Tris-300 mmol l(-1) boric acid buffer (pH 7.0) containing an achiral crown ether (18-crown-6). Enantiomeric separations of two neutral compounds were also achieved using 200 mmol l(-1) Tris-300 mmol l(-1) boric acid buffer (pH 9.0) as a mobile phase. High efficiencies of up to 150,000 plates m(-1) were obtained. Both the within- and between-run reproducibilities of retention time and separation factor were good. The reproducibilities of retention time and separation factor for three different columns prepared from a different batch of monomers were acceptable. The gel-filled capillaries were stable for at least 3 months with intermittent use, utilizing the mobile phase of 200 mmol I(-1) Tris-300 mmol I(-1) boric acid buffer (pH 9.0).     

Fixation of a cholesteric helical structure by the photopolymerization of a cholesteryl derived monomer

A cholesteryl derived monomer was synthesized according to a conventional synthetic route; it exhibits a cholesteric phase above 129°C, and shows a red colour due to selective reflection in the cholesteric phase. Photopolymerization of the monomer was carried out at 135°C in the cholesteric phase. The helical structure of the cholesteric phase of the monomer was frozen by photopolymerization. A peak based on the selective reflection of the cholesteric phase was detected at 615 nm in the transmittance UV-Vis spectrum. Mixtures of the monomer with a binaphthyl derivative were prepared to control the selective reflection wavelength; they all also exhibited a cholesteric phase. The selective reflection wavelength of the mixture was dependent upon the ratio of the binaphthyl derivative in the mixture. This wavelength became shorter with increasing ratio of the binaphthyl derivative. The polymer films obtained by photopolymerization displayed almost the same selective reflection wavelength as the corresponding mixtures before photopolymerization. The selective reflection wavelength of the polymer films did not change up to about 250°C.     

Building a Simple Model of a Pulse-Frequency-Modulation Photosensor and Demonstration of a 128 x 128-pixel Pulse-Frequency-Modulation Image Sensor Fabricated in a Standard 0.35-$mUm Complementary Metal-Oxide Semiconductor Technology

We present a simple model of the pulse-frequency-modulation (PFM) photosensor that provides explicit relationships between circuit parameters and output characteristics. The model treats the PFM photosensor with a feedback loop as an open loop circuit. Several characteristics such as output pulse frequency for light intensity and photosensitivity are expressed by device parameters of a photodiode, reset transistor, and chain of inverters. The relationships derived from the proposed model help us to comprehend the results by simulation program with integrated circuit emphasis (SPICE) or experiments. We design and fabricate a 128 x 128-pixel PFM image sensor with photosensitivity of 0.15 Hz/lux. As a demonstration, a figure of a dinosaur is captured using the fabricated image sensor to discuss its operation. Characteristics of a normal pixel and white and black defect pixels are measured and discussed based on the results of formulations.