Syntheses of gramicidin s analogs containing D-Serine or a dehydroalanine residue,and asymmetric hydrogenation of the dehydroalanine

Gramicidin S (GS) analogs, (D-Ser(Bzl)^4,4′]-GS ($\text{17}$), [D-Ser^4,4′]-GS ($\text{18}$), and [L-Orn(Boc)^2,2′,D-Ser^4,4′]-GS ($\text{19}$) were synthesized and $\text{17}$ showed high antibacterial activity. One residue of D-Ser in $\text{19}$ was converted asymmetrically to D-Ala via α,β-dehydroalanine.     

Oxidation of Two α-Hydroxy Acids by Vanadium(V)

Summary. The pathways for the oxidation of tartaric acid and citric acid by vanadium(V) in perchloric acid medium have been studied at 303K by following the formation of vanadium(IV) spectrophotometrically at 760nm. The oxidation reaction displays fractional order dependence with respect to both the -hydroxy acids concentrations as well as fractional (tartaric acid) and first order (citric acid) dependencies with respect to the perchloric acid concentration. It does not matter at all whether the ionic strength was varied or was maintained constant. The reaction rate remains essentially constant with increasing ionic strength in the tartaric acid oxidation, but decreases slightly in the citric acid case. A decrease of the dielectric constant of the reaction medium results in a rate decrease in the tartaric acid oxidation and in a rate enhancement in the citric acid reaction. The activation parameters were obtained from studies of the reactions at different temperatures (293 to 313K). Based on the experimentally determined rate laws oxidation mechanisms and theoretical rate laws were proposed.Received April 8, 2003; accepted May 10, 2003 Published online September 18, 2003     

Studies of intrarenal distribution by macroautoradiogram and tissue distribution of 99mTc-gluconate (author's transl)]

1) The experimental studies have demonstrated that 99mTc-gluconate reaches a high concentration in the kidneys within 1-2 hours after injection and its concentration in organs adjacent to the kidney is low. 2) The initial images of serial macroautoradiograms visualized the inner medulla as well as the cortex and outex medulla, whereas the delayed images revealed only the outer cortex and outer stripes in the outer medulla. These findings suggest that this renal agent consists of two components and the delayed component deposits in the convoluted and straight segments of proximal tuble. 3) This renal agent visualizes the calyceal system and excretory pathways in the initial study and the renal morphology in the delayed study. Therefore, using this renal agent, it may be possible to evaluate a variety of renal diseases, including obstructive uropathy, space-occupying lesions, congenital deformities, etc,.     

Interaction of Chlorine with Hydrogenated Diamond Surface

The interaction of chlorine with the hydrogenated diamond surface has been investigated by diffuse reflectance Fourier-transform Infrared (FTIR) spectroscopy, temperature-programmed desorption (TPD) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The hydrogenated diamond surface is chlorinated by thermal reaction in chlorine. Hydrogen chemisorbed on the diamond surface is abstracted by chlorine and the chemisorption of chlorine is yielded. Hydroxyl groups are produced by treatment of the chlorinated diamond with water vapor at room temperature. Amino groups are produced by treatment of the chlorinated diamond with ammonia at 425 °C.     

First total syntheses of the phytotoxins solanapyrones D and E via the domino Michael protocol

The phytotoxins solanapyrones D (1) and E (2) have been synthesized from the decalone prepared by the domino Michael reaction of the kinetic enolate of optically pure acetylcyclohexene with methyl crotonate. The decalone was transformed into a solanapyrone core by equilibration into thermodynamically stable trans-decalone (11), dehydroxylation, and dehydration. Condensation of a methyl acetoacetate equivalent followed by cyclization installed a pyrone moiety. Introduction of a formyl or hydroxymethyl unit into the pyrone ring via Pummerer related reactions furnished solanapyrones D (1) and E (2).     

Characterization of geometrid sex pheromones by electrospray ionization time-of-flight mass spectrometry

The utility of liquid chromatography combined with time-of-flight mass spectrometry (LC/TOFMS) was demonstrated for studies on chiral unsaturated epoxy compounds, sex pheromones produced mainly by female moths in the family Geometridae. By electrospray ionization (ESI), each synthetic epoxyalkadiene derived from (Z,Z,Z)-3,6,9-triene with a C(18)-C(23) straight chain showed three ion series, [M + NH(4)](+), [M + H](+) and [M - OH](+), with high resolution and good sensitivity, indicating its molecular formula. In addition to these, characteristic fragment ions at m/z M - 57 and M - 71 for the 3,4-epoxides and at m/z M - 123 and 123 for the 9,10-epoxides were detected, whereas the 6,7-epoxides did not produce fragment ions that reflected their structures. Monitoring these diagnostic ions during the LC/MS analysis of a gland extract, the natural sex pheromone of the mulberry looper was confirmed to be (Z,Z)-cis-9,10-epoxy-3,6-octadecadiene, which was separable from the other positional isomers on an ODS column. Furthermore, (Z,Z)-cis-3,4-epoxy-6,9-nonadecadiene secreted by the Japanese giant looper was analyzed with a chiral column, and the stereochemistry was determined directly.     

Sulfurization of 1,4,7,10-tetraarylcyclododeca-1,2,3,7,8,9-hexaenes

Thermal reactions of 1,4,7,10-tetraarylcyclododeca-1,2,3,7,8,9-hexaenes1a and1b with elemental sulfur were examined, and found to give novel transannular bridged pentasulfides2a and2b, while cyclopentenethiones3a and3b were obtained by the sulfurization of1a and1b in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene.     

Matrix isolation of silaacrylate and its photochemical reaction

π-Bonded silaacrylate was isolated in argon matrix at 10K by the photolysis (λ > 360 nm) of ethyl pentamethyldisilanyldiazoacetate. The silaacrylate immediately changed to (ethoxydimethylsilyl) (trimethylsilyl)-ketene at 10K by the brief irradiation with the light of shorter wavelength (λ > 240 nm).