摘要:

Structure and Design of Cyclic Peptides for the Regulation of the Immune SystemThe immune system of higher animals is regulated and can be influenced by a number of peptides and small proteins. Enhanced activity, selectivity and metabolic stability can be achieved by cyclization of bioactive parts of these peptides, provided the bioactive conformation is matched correctly. Several cyclic peptidic antibiotica are found which stimulate or suppress immune response. It is demonstrated how modern NMR spectroscopy in combination with molecular dynamics calculations can be used to determine the conformation of these compounds in solution. This article emphasizes the work of the author in this field.

ISSN:0941-1216    

DOI:10.1002/prac.19923340702

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

Synthesis of 7‐Alkylidene‐tricyclo[6.3.0.02,6]undeca‐4,9‐diene‐3,11‐dionesThe cycloaddition reaction of 6‐alkyl‐ as well as 6,6‐dialkyl substituted pentafulvenes1a – fwith 1,4‐benzoquinone proceeded efficiently and highlyendo‐stereoselectively when water was used as the solvent. The adducts2a – feasily underwent intramolecular photocycloaddition when irradiated in acetone or cyclohexane. The resulting trishomocubanediones3a – fcould be transformed into linearly fused tricyclopentanoids4a

ISSN:0941-1216    

DOI:10.1002/prac.19923340703

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractPhenols1substituted in the para position by vinyl groups bearing different combinations of thioether and cyano substituents in the β positions were synthesized. The determination of their efficiency as antioxidants led to the following order of reactivity: RS,RS ≫ RS,CN>CN,CN. The analysis of the ESR spectra of analogous phenoxy radicals4indicates however a different order for the radical stabilization: RS,CN>RS,RS ≫ CN,CN. This behavior is explained by a charge or electron transfer in the transition state as the main factor governing the reactivity. Relative stabilizations of the phenoxy radicals are easily explained according to the captodative con

ISSN:0941-1216    

DOI:10.1002/prac.19923340704

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe β‐azide of O‐acetyl protected N‐acetyl glucosamine is efficiently accessible via a phasetransfer‐catalyzed reaction of the corresponding glycosyl chloride with sodium azide. The azido group revealed to be a useful anomeric protection for modifications of the protecting group pattern of the glucosamine unit. Exchange of the O‐acyl groups by 4‐methoxybenzylidene and 4‐methoxybenzyl (Mpm) protection delivered regioselectively blocked glucosaminyl azide derivatives. In contrast, the N‐phthaloyl protected glucosaminyl azide was obtained quantitatively from the corresponding glycosyl fluoride via a boron trifluoride‐promoted reaction with trimethylsilyl azide. N‐Phthaloyl glucosaminyl fluoride was also revealed to be useful in the synthesis of β‐glucosamine glycosides and saccharides. Chitobiosyl azide21carrying a selectively removable 6‐O‐Mpm protection was synthesized from the O‐acetyl protected N‐phthaloyl glucosaminyl bromide and N‐acetylglucosaminyl azide13as an acce

ISSN:0941-1216    

DOI:10.1002/prac.19923340705

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

AbstractThe 4‐methoxybenzyl (Mpm) group removable by selective oxidation was applied as a nonneighbouring‐group‐active protection of fucose hydroxy functions in the stereoselective synthesis of α‐fucosides of acceptors containing double bonds sensitive to hydrogenation. With this aim, the synthesis of the α‐fucosyl chloride (4) carrying the acidsensitive Mpm protection was

ISSN:0941-1216    

DOI:10.1002/prac.19923340706

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

Adsorption of Vinyl Chloride on Activated Carbons, Adsorber Polymers and Zeolites. I. Isotherms of AdsorptionThe adsorption of vinyl chloride on activated carbons, adsorber polymers and zeolites has been investigated by a gravimetric adsorption apparatus in order to determine the adsorption capacities. The form of the isoterms is mainly influenced by the structure of the adsorbents. The isotherm of the zeolites is strongly curved whereas the isotherms of the polymers have a low slope. The experimental isotherm data of the different adsorbents can be well described by modified Langmuir equations. The adsorption capacities of the different carbon adsorbents determined show a good correlation to the specific surface area.

ISSN:0941-1216    

DOI:10.1002/prac.19923340707

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

Degradative and Dismutation Reactions of CHCl3‐nFn‐Fluorochlorocarbons on Modified – Aluminium Oxide CatalystsThe degradative processes and dismutation reactions of haloalkanes of the CHCl3‐nFn‐series during the activation of a γ‐Al2O3‐catalyst were studied. The following main degradative products were obtained: carbon monoxide, hydrogen chloride, water and different Al‐F‐species on the surface of the solid. Competitive reactions were separated by changing the experimental conditions. The layer of different Al‐F‐species on the surface, which is formed during the activation, is more active for catalyzing dismutation reactions than the pure hydroxide and oxide surface. The results are explained in connection with thermodynamical considerations, and a mechanism of degradative

ISSN:0941-1216    

DOI:10.1002/prac.19923340708

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

On the Allyl‐Cyclopropyl Isomerism of Substituted Cations: An AMl and MNDO StudyThree series of cations (2‐X‐allyl cations (1), 1‐X‐cyclopropyl cations (2) and 1‐X‐isopropyl cations (3)) were investigated by both the MNDO and AMl quantum chemical methods. For π‐electron donators (X = NH2, OH, NHOH) derivatives2are more stable than1. The opposite is valid for derivatives with δ‐electron acceptors (X = NO2, CHO, halogens). AMl values are closer to experimental or ab initio heats of formation than MNDO results. Therefore, by means of AMl only, reasonable ringstrain energies were obtained for2, while the MNDO method failed in all investigated cases. It has been shown that the unknown 2‐hydroxyaminoallyl cation is probably more stable than its

ISSN:0941-1216    

DOI:10.1002/prac.19923340709

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

Photocrosslinking of Silicones. VII. The Influence of the Silicone Backbone – a Kinetic StudyThe photo‐induced radical crosslinking of silicone containing pendant acrylate groups was investigated by nanosecond flash photolysis and photocalorimetry. From the results of the flash photolysis is inferred that the photochemically formed benzoyl radicals react with the acrylate groups of the system. A possible H‐abstraction from the methyl groups of the silicone backbone was not observed. The silicone backbone functions only as an internal solvent. Calorimetric measurements with model systems support these results.The polymerization process is inhibited by oxygen. From calorimetric results is inferred that oxygen both inhibits and terminates the polymerization process. Due to their high oxygen solubility the silicone units increase the oxygen influence on the crosslinking.The calorimetric measurements shows also that a direct bond between silicone backbone and the acrylate group reduces the oxygen influence. Also, in absence of oxygen a direct bonded acrylate group accelerates the polymerization

ISSN:0941-1216    

DOI:10.1002/prac.19923340710

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY

摘要:

1,3‐Acylrearrangements by Cyclisation of Thioureas with Imidochlorides of Oxalic Acid – An Approach to interesting Thiocarbonylic SystemsBy cycloacylation of various substituted thioureas with bis‐imidochlorides of oxalic acid the new thiazolidines3, 4and isomeric imidazolidines5, 6are obtained. Especially when triethylamine is used as a base the main products are the deeply coloured 4‐arylimino‐5‐thioxo‐imidazolidines which can be regarded as s‐cis‐configurated 1,4‐dihetero‐1,3‐dienes. Some thiazolidines can be rearranged by means of anhydrous organic acids to parabanic acid derivatives; whereas the 5‐thioxo‐imidazolidines result from an intramolecular 1,3‐acyl rear

ISSN:0941-1216    

DOI:10.1002/prac.19923340711

出版商:WILEY‐VCH Verlag GmbH    

年代:1992

数据来源: WILEY