Synthese von β-D-Glucopyranosiden einiger hydroxylierter Vitamin-D-Verbindungen

Synthesis of β-D -Glucopyranosides of some Hydroxylated Vitamin-D Compounds Cholesta-5, 7-diene-1α, 3β-diol (1a) was glycosylated with ‘α-acetobromoglucose’ (2) as well as with ‘α-acetobromocellobiose’ (4) to yield the 3-(glycosides) 1b and 1c , respectively. Irradiation of these products with UV light followed by thermal isomerization led to the corresponding vitamin-D derivatives 3a and 3c. Direct glucosylation of vitamin D₃ (3f) and vitamin D₂ (5a) with 2 gave the derivatives 3g and 5b , respectively. With 25-hydroxycholecalciferol ( = calcidiol; 6a ) as substrate, besides the 3-(glucoside) 6b small amounts of the C(25)-analog 6c were formed. The reaction of 1α, 25-dihydroxycholecalciferol ( = calcitriol; 6e ) with 2 furnished the 3- and the 1-(glucoside) ( 6f and 6g , respectively) as the major components and the C(25)-analog 6h in minor quantity. From the acetylated 3-(glucosides) 3a, 3g, 5b, 6b , and 6f , the free glucopyranosides 3b, 3h, 5c, 6d , and 6i , respectively, were prepared as well as the free glucopy-ranosyl-glucopyranoside 3d from the acetylated disaccharide 3c.     

An investigation into the initial degradation steps of four major dye chromophores: study of their one-electron oxidation and reduction by EPR, ENDOR, cyclic voltammetry, and theoretical calculations

The degradation of dyes is frequently initiated by one-electron oxidation or reduction; however, relatively little is known about the initially formed radicals. Acid Green 25 (AG25), Crystal Violet (CVI), Methylene Blue (MB), and Acid Orange 7 (AO7), representing paradigms of four types of commercial organic dyes, were therefore investigated in terms of their redox behavior. Their redox potentials in MeCN and buffered aqueous solutions were determined by cyclic voltammetry. The structures of the one-electron reduced and oxidized dyes were established by EPR spectroscopy and by theoretical calculations on the density functional level of theory.     

A complete closed form vectorial solution to the Kepler problem

The paper gives an exact vectorial solution to the Kepler problem. A vectorial regularization that linearizes the Kepler problem is given using a Sundman transformation. Closed form expressions describing the Keplerian motion are deduced. A unified approach to the classic Kepler problem is offered, by studying both rectilinear and non-rectilinear Keplerian motions with the same instrument. The approach is an elementary one and only simple vectorial computations are involved.     

Screening of medicinal plants traditionally used in Peruvian Amazon for in vitro antioxidant and anticancer potential

Plants mentioned in this study have numerous records in traditional Peruvian medicine being used in treatment of cancer and other diseases likely to be associated with oxidative stress. Amongst the eight plant species tested, only Dysphania ambrosioides exhibited combinatory antioxidant and anti-proliferative effect on a broad spectrum of cancer cells (DPPH and ORAC values = 80.6 and 687.3 μg TE/mg extract, respectively; IC₅₀ against Caco-2, HT-29 and Hep-G2 = 129.2, 69.9 and 130.6, respectively). Alkaloids and phenolic compounds might significantly contribute to anticancer/antioxidant activity of this plant. The results justify the traditional medicinal use of this plant. Our findings further suggest that D. ambrosioides might serve as a prospective material for further development of novel plant-based antioxidant and/or anti-proliferative agents. Detailed analysis of chemical composition together with toxicology assessments and in vivo antioxidant/anti-proliferative activity of this plant should be carried out in order to verify its potential practical use.     

Fabrication of buried waveguides in planar silica films using a direct CW laser writing technique

A CW CO₂ laser ablation technique is used to form buried waveguides in planar silica films. It is shown that the refractive index of a silica thin film is reduced sufficiently adjacent to the laser processed region to allow the fabrication of low loss waveguides. The refractive index distribution of these structures is measured using the reflectance of a focussed spot from the surface of the films. The change in refractive index is measured to be of the order of the core cladding refractive index difference of typical single mode waveguides. The spatial resolution of the reflectance technique is 1.3 μm with a refractive index resolution of ±5 × 10^?4. Devices such as 1 × 2 and 1 × 4 multi-mode interference (MMI) splitters have also been demonstrated and shown to exhibit low transmission losses.     

Synthesis of an N-Acetylated Heparin Pentasaccharide and its anticoagulant activity in comparison with the heparin pentasaccharide with high anti-factor-Xa activity

The synthesis of tri-N-acetylated heparin pentasaccharide 2 is described. It was assembled from five suitably blocked monosaccharide units ( 3 – 7 ). Glucuronic-acid building block 4 was prepared from glucose by direct Jones oxidation of the 6-O-trityl derivative 18 . The resulting acid 16 was esterified to 17 in large mounts using methyl chloroformate/base. Trimethylsilyl bromide proved to be an excellent reagent for the hydrolysis of a prop-1-enyl glycoside ( 19 →21 ). The pentasaccharide 29 was obtained by a [2 + 2] + 1 synthesis, the glycosylation reactions furnished good to very good yields. The identity of protected oligosaccharides was confirmed by ¹H-NMR spectroscopy. Sequential deblocking of the pentasaccharide, O-sulfation, and N-acetylation gave 2 which was shown to exhibit ca. 600 times lower anticoagulant activity than pentasaccharide 1 .     

Reactivity of 1-chloro-3-phenyldiazirines

p-Substituted 1-chloro-3-phenyldiazirines (5), the putative intermediates of the reaction of N,N,N'-trichlorobenzamidines (10) with excess of bromide ions, react further to afford mixtures of 3-bromo- (4) and 3-chloro-3-phenyldiazirines (6). The 6:4 ratios inversely correlate with the Hammett sigma(p) and sigma(p)+ constants of the p-substituents. The formation of 4, proposed to proceed by anti-S(N)2' mechanism, is predominant with electron-withdrawing p-substituents. Compounds 6, the major products with electron-donating p-substituents, may arise from 5 by a [1,3]-sigmatropic shift of chlorine proceeding via polar transition structures 12. The results of a gas-phase DFT (B3LYP/6-31+G*) study on the two mechanisms are consistent with experiment.     

Some inequalities concerning the characteristic frequencies of elastic continuum

Summary We consider the boundary value problem αz″(x)+m(x)y(x)=0, αy″(x)+p(x)z(x)=0, xε[0, 1], y(0)=y(1)=z(0)=0, where the functions m(x) and p(x) are assumed integrable and positive everywhere in [0, 1]. As the main result we obtain the inequalities for n=1, 2, ... where δ_n(m, p) stands for the product of the first n eigenvalues α_i(m, p) of the above system and where δ_n(m) abbreviates δ_n(m, m). Entrata in Redazione il 6 febbraio 1976.