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11.
Reaction of the vicinal diols of steroids1, 5, 7, 10, 13, and16 with TPP/DEAD yields both regio-and stereospecifically the oxosteroids2, 6, 8, 11, 14, and15 by displacement of an axial hydrogen and extrusion ofTPPO besides the cholest-4-en-6-ols9 and12 and the cyclic carbonate3. 16, 17-androstandiol16 gives only the cyclic carbonate17. The different structures of the carbohydrates withcis-diol arrangement19 and21 lead exclusively to cyclic carbonates20 and22 in moderate yields. Treatment of1 with TPP/DEAD/HN3 affords 3-azido-2-hydroxycholestane4 in addition to the above mentioned2. 相似文献
12.
The azido tetrazolo valence isomerism of twenty 9-methyl-s-triazolo[4,3-c]tetrazolo[1,5-a]pyrimidines with different substituents at position 5 has been studied by means of 1H NMR spectroscopy. All the compounds have been found to be tetrazoles in the solid state and in (CD3)2SO solution; in CF3COOH azido and tetrazolo isomers are in equilibrium. From equilibrium constants K and thermodynamic data determined it is concluded that in this series K depends on both electronic effects and steric requirements of the 5-substituents. A linear relation between K and σ was found for 5-arylderivatives because ΔS° keeps approximately constant and the substituent mainly operates on ΔH°. 相似文献
13.
3-O-Acetyl-1,2-O-isopropylidene--D-allofuranose (2 b) was prepared from 1,2:5,6-di-O-isopropylidene--D-allofuranose (1 b). Treatment of2 b with triphenylphosphine-diethyl azodicarboxylate afforded regio- and stereospecifically the 5,6-epoxy--D-allo derivative (3). The other diastereomeric compound, 5,6-epoxy-1,2-O-isopropylidene--L-talofuranose (6) was also prepared stereoselectively from2 b
via the intermediates5 a and5 b. The epoxy sugars3 and6 were converted with lithium aluminum hydride to the corresponding 6-deoxy-1,2-O-isopropylidene--D-allofuranose (4 a) and --L-talofuranose (7 a) derivatives. Hydrolysis of4 a and7 a afforded 6-deoxy-D-allose and 6-deoxy-L-talose, respectively. The corresponding 3,5-di-O-acetyl- (4 b and7 b) and the 3,5-O-(tetraisopropyldisiloxane-1,3-diyl) derivatives (4 c and7 c) are also described. Selective removal of the isopropylidene group and subsequent acetylation offers a convenient route to prepare sugar derivatives containing furanose ring, like8 b, as a suitable precursor for nucleoside analogs.Herrn Prof. Dr.K. Komarek mit den besten Wünschen zum 60. Geburtstag gewidmet. 相似文献
14.
On the Activation of Partially Silylated Carbohydrates Using Triphenylphosphane/Diethylazodicarboxylate Reaction of methyl α-D-glucopyranoside ( 1 ) with two equivalents of t-butyldimethylchlorosilane yields methyl 2,6-bis[O-(t-butyldimethylsilyl)]-α-D-glucopyranoside ( 1a ) and methyl 3,6-bis[O(t-butyldimethylsilyl)]-α-D-glucopyranoside ( 1b ) in a ratio of 4:1. The anomeric β-pyranoside 2 affords methyl 2,6-bis[O(t-butyldimethylsilyl)]-β-D-glucopyranoside ( 2a ) and methyl 3,6-bis[O(t-butyldimethylsilyl)]-β-D-glucopyranoside ( 2b ) in nearly equal amounts. 2b is isomerized to methyl 4,6-bis[O(t-butyldimethylsilyl)]-β;-D-glucopyranoside ( 2c ) (83%) and 2a (10%) with triphenylphosphane/diethylazodicarboxylate. Structures were assigned by NMR.-analysis and CD.-analysis of the corresponding benzoates 1c , 1d and 2d and of the acetates 2e and 2f . 1a is transformed into methyl 4-azido-2, 6-bis[O(t-butyldimethylsilyl)]-4-deoxy-α-D-galactopyranoside ( 3 ) with triphenylphosphane/diethylazodicarboxylate/HN3. 2a and 2c yield the 3-azido-allosides 5 and 7 respectively under similar conditions. The activation by triphenylphosphane/diethylazodicarboxylate is high enough to introduce also p-nitrobenzoate groups with inversion of configuration at the reaction center. By this way 1a and 2a give methyl 2, 6-bis[O(t-butyldimethylsilyl)]-4-O-p-nitrobenzoyl-α-D-galactopyranoside ( 4 ) and methyl 2, 6-bis[O-(t-butyldimethylsilyl)]-3-O?ptrobenzoyl-β-D-allopyranoside ( 6 ) respectively. For elucidation of structures the acetate derivatives 3a-7a were prepared. 相似文献
15.
From methyl-5-acetylamino-7,8-anhydro-4,9-O-bis-(t-butyldimethylsilyl)-3,5-dideoxy--D-glycero-D-galacto-2-nonulopyranosidonic acid methylester (1) the derivatives1 a and1 b were obtained by removing the 9-O-(t-butyldimethylsilyl)group withBu
4NF, followed by acetylation. Treatment of1 b with 80% acetic acid and acetanhydride/pyridine yields the 8-epi-N-acetylneuraminic acid derivative2 a and the 7-epi-N-acetylneuraminic acid derivative3 a in a ratio of 3:1 (Scheme 1). The structure elucidation of2 b was achieved by converting2 b via the 4,9-bis-O-(tBDMSi)-8-O-tosyl-derivative2 d into the epoxide1 (Scheme 2). Using the same sequence the epoxides4 and5 were transformed into theN-acetylneuraminic acid derivative6 a and the 7,8-bis-epi-N-acetylneuraminic acid derivative7 a (Scheme 3). After treatment with sodium hydroxide and 0.025m HCl and Dowex 50 H+ the 8-epi-, 7-epi- and 7,8-bis-epi-N-acetylneuraminic acids2,3, and7 were obtained. These three compounds were tested withCMP-N-acetylneuraminic acid synthetase.
Herrn KollegenK. Schlögl mit den besten Wünschen zum 60. Geburtstag. 相似文献
16.
Summary We start with a measurem on a measurable space (,A), decomposable with respect to an Archimedeant-conorm on a real interval [0,M], which generalizes an additive measure. Using the integral introduced by the second author, a Radon-Nikodym type theorem, needed in what follows, is given.The integral naturally leads to a -decomposable measurem on the space of all measurable functions from to [0, 1]. The main result of the present paper is the converse of this, namely that, under natural conditions, any -decomposable measurem on can be represented as an integral of a certain Markov-kernelK.
We extend this representation to measures
on which have values in a set of distribution functions.These results generalize the work done by the first author in the case of additive measures. 相似文献
17.
LetG be a subgroup of the general linear group GLn(K), where charK 2. Put Kn =V. AssumeG is generated by the setS of all elements inG for which dimV( – 1) = 1, and suppose 2=1V for each inS. If {V(–1)¦S} contains a simplex, if – 1V G, and if inG is a product of dim v(–1) elements inS wheneverV(–1) is not contained in the kernel of–1, thenG is a subgroup of an orthogonal group.This research was supported in part by NSERC Canada grant A7251.To Helmut Mäurer on his 60th birthday 相似文献
18.
Erich Königsberger Lan-Chi Königsberger Glenn Hefter Peter M. May 《Journal of solution chemistry》2007,36(11-12):1619-1634
Isopiestic measurements of mixed electrolyte solutions involving sodium hydroxide and other components of Bayer liquors were performed at 50?°C and 100?°C. Most of the systems studied obey Zdanovskii’s rule exactly or very closely. However, those with sodium chloride as one of their components show deviations from Zdanovskii’s rule, which are well predicted by our thermodynamic modelling software based on Pitzer’s equations. 相似文献
19.
Erich Knözinger 《Fresenius' Journal of Analytical Chemistry》1976,278(3):177-190
Zusammenfassung Es werden praktische Erfahrungen beim Einsatz der FIR-Fourier-Spektroskopie im Bereich der Chemie besprochen. Dabei wird auf die folgenden vier Themen eingegangen: Anforderungen an die Geräte; Auswahl der Geräteparameter; Probenpräparation; Qualitative Interferogrammauswertung.
Practical aspects of FIR Fourier Spectroscopy in chemistry
Practical techniques in the application of FIR Fourier Spectroscopy to chemistry are described. The discussion concerns the following four topics: instrumental requirements; selection of instrumental parameters; sample preparation; qualitative interferogram evaluation.相似文献
20.
The crystal structure of the title compound has been determined from single crystal X-ray diffraction data and refined toR=0.125. The unit cell is triclinic, space group P,
(No. 2),a=5.688(1),b=5.701(1),c=8.583(1) Å, =81.32(1), =71.50(1), =67.95(1)° andZ=2. The structure consists of isolated [GeO4] tetrahedra linked together by four- and five-coordinate sodium atoms. Na4GeO4 is isostructural with Na4CoO4 (which has been described to be non-centrosymmetric and for which a centrosymmetric model is presented), K4GeO4, K4SnO4 and K4PbO4. 相似文献