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101.
Peter Rüedi Jean Martin Schmid Roland Prewo Jost Hans Bieri Conrad Hans Eugster 《Helvetica chimica acta》1983,66(2):429-449
Spirocoleons: Synthesis and Characterization of Four Diastereomeric Spiro (methylcyclopropane) Substructures; Revision of the Configuration at C(12) and C(15) of Coleon P and Derivatives and Coleon-Z Derivatives; X-Ray Analysis of Lanugon J and of Further Spirocoleons X-ray analyses show the correctness of the previously published structure of coleon Q (1) , establish the structure of lanugon J (4a) , and necessitate a revision of the configuration at C(12) and C(15) in coleon P (3a) and its derivatives 3b and 3c , and furthermore of the coleon Z derivatives 11a–11d . Two further diastereomeric spiro (methylcyclopropane) substructures have been generated by photoisomerization of lanugon J (4a) and 12-O-desacetylcoleon N (8) ; they represent the novel cis-type B with (12R, 13R, 15S)- and the novel trans-type D with (12R, 13R, 15R)-configuration (Scheme 1). The structures of the photoproducts 5a ((12R, 13R, 15R)-lanugon J) and 7a ((12R, 13R, 15S)-lanugon J) were established by X-ray analysis. So far, only two of the eight possible diastereomers of the spiro-(methylcyclopropane) substructure I have been detected in nature, i.e. the trans-type A with (12R, 13S, 15S)- and the cis-type C with (12R, 13S, 15R)-configuration. The four diastereomers A-D , all possessing (12R)-configuration, show very similar properties. However, careful comparison of spectral and chiroptical data allow a differentiation, even in the case of functionalization of H3C(17). The (12S)-counter-parts could not yet be prepared. 相似文献
102.
Esam Khalifa Abhoy N. Ganguly Jost H. Bieri Max Viscontini 《Helvetica chimica acta》1980,63(8):2554-2558
A Convenient Synthesis of Leucovorin The synthesis of leucovorin, a 5-formyl-(6R or S)-5,6,7,8-tetrahydropteroyl-L -glutamic acid (II) is described. The L -folic acid was first reduced to (6R, S)-tetrahy-dro-L -folic acid (I); formylation with methyl-formate in DMSO gave directly leucovorin (as a diastereomeric mixture) in good yields. To demonstrate, that the formylation occurred regiospecifically at N (5) and not at N (10), N (10)-nitroso-(6 R, S)-tetrahydro-L -folic acid was formylated under the same conditions. Reductive elimination of the N (10)-nitrosogroup gave the identical leucovorin as in the previous case. The synthetic leucovorin was biologically as active as the natural product with Streptococcus faecalis ATCC 8043 and Pediococcus cerevisiae ATCC 8081. 相似文献
103.
Bernhard Hostettler Jean Pierre Obrecht Roland Prewo Jost H. Bieri Heinz Heimgartner 《Helvetica chimica acta》1986,69(2):298-304
5,6,7,8-Tetrahydro-4H-1,2,5-oxadiazocin-6-ones, Ring Enlargement Products from a 3-Isoxazolidinone and 3-Amino-2H-azirines 3-Dimethylamino-2H-azirines 1 and 4,4-dimethyl-3-isoxazolidinone ( 7 ) undergo already at room temperature a ring enlargement reaction to yield 5,6,7,8-tetrahydro-4H-1,2,5-oxadiazocines of type 8 . The structure of 8a has been confirmed by X-ray crystallography. The conformation of the eight-membered ring with a trans-amide group is of particular interest (Fig. 1 and 2). 相似文献
104.
Abstract. Flash photolytic experiments with suspensions of rod particles isolated from cattle eyes reveal that at low temperatures a transient is formed following irradiation which preceeds lumirhodopsin in the bleaching process. Kinetic studies, in the range -75°C to -50°C, suggest that the transient is composed of three intermediate species, having similar absorption spectra but changing to lumirhodopsin at different rates. The energies of activation of the decay reactions appear to be identical and equal 12.5°3 kcal/mole. Spectrophotometric experiments have demonstrated that the low temperature transient is stable at liquid nitrogen temperatures and suggest that it can be reversibly converted to a mixture of rhodopsin and isorhodopsin at -195°C.
A detailed comparison of light initiated reactions of rhodopsin in rod particle suspensions and in solutions reveals striking similarity in the two systems. 相似文献
A detailed comparison of light initiated reactions of rhodopsin in rod particle suspensions and in solutions reveals striking similarity in the two systems. 相似文献
105.
Jürgen Jost 《manuscripta mathematica》1986,56(3):279-291
We show c1,-regularity of minimal surfaces in Riemannian manifolds with a free boundary on C2-hypersurfaces with bounded second fundamental form and a uniform neighborhood on which the nearest point projection is uniquely defined and differentiable. The decisive step is the proof of continuity at the free boundary.partially supported by SFB 72 (Deutsche Forschungsgemeinschaft) 相似文献
106.
Summary The introduction of a cyano-modified, pre-coated layer substantially widens the selectivity of stationary phases in thin-layer
chromatography. This is a moderately polar sorbent based on silica gel 60, which can be used both in adsorption chromatography
and in reversed-phase chromatography. This new pre-coated layer is particularly suitable for separation of steroids, alkaloids
and derivatized amino acids. The possibility of separating habitforming drugs and preservatives in the presence of ionpair
reagents is also discussed. 相似文献
107.
108.
109.
110.
Paulo C. Nascimento Luciana Didonet Del-Fabro Cristiane Luisa Jost Denise Bohrer Leandro Machado de Carvalho Marcelo Barcellos Rosa 《Journal of Analytical Chemistry》2009,64(7):677-682
A spectrophotometric method for simultaneous determination of Al(III) and Fe(III) using the chelator Desferal® (desferrioxamine B) was developed. Partial least squares (PLS) regression was performed to resolve the overlapped signals obtained from Al(III) and Fe(III) complexes. The parameters controlling behavior of the system were investigated and optimum conditions were selected. PLS was the choice for the analysis of binary mixtures of Fe(III) and Al(III) over the range of 0.1 to 0.8 mg L?1 by using the data of first derivative spectra. Absorbance data were taken between 200 and 600 nm. The calculated sensitivity values for the multivariate method were 4.88 and 5.64 for Al(III) and Fe(III), respectively. Multivariate detection limits were 0.075 and 0.064 mg L?1 for Al(III) and Fe(III), respectively. The method was applied to real post-hemodialysis samples, and sample digestion by UV irradiation was discussed. 相似文献