ISSN:0165-0513    

DOI:10.1002/recl.19881071202

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractA conformational‐analysis study based on 500‐MHz1H NMR and circular dichroism (CD) has been performed on the branched trinucleotide U‐5′‐3′‐A‐2′‐5′‐G (1) which models the branch point in the lariat structure of Group‐II excised introns. The NMR and CD results are in agreement with previous work in which it was shown that adenine 2′‐5′ guanine base stacking essentially determines the molecular conformation of compound1. The ribose ring of the A residue shows a preference for theSconformation, while the riboses of U and G are highly flexible,i.e.no clear preference forNorSis observed. CD spectroscopy of1showed that ethylene glycol leads to disruption of adenine 2′‐5′ guanine stacking. Furthermore, we studied the unnatural branched trinucleotide G‐5′‐3′‐A‐2′‐5′‐U (2) in which U and G are reversed in comparison with compound1. The molecular conformation of2is far more rigid in comparison with1, as a result of very strong adenine 2′‐5′ uracil stacking. Ethylene glycol was apparently unable to facilitate de‐stacking of adenine and uracil in2. The present results show that guanosine as the 2′linked nucleotide corresponds with a clear molecular flexibility. This may be of relevance in understanding why guanosine, as the 2′‐5′ nucleotide, is

ISSN:0165-0513    

DOI:10.1002/recl.19881071203

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe sulfonation of methyl phenyl sulfate (4) with concentrated aqueous sulfuric acid at 25°C yields the 4‐sulfonic acid. This initial product then decomposes to give phenol‐4‐sulfonic acid, which is subsequently sulfonated to phenol‐2,4‐disulfonic acid. From the first‐order‐rate coefficients obtained for sulfonation of phenyl methanesulfonate (3) and (4) in 93.2% H2SO4, for which acid concentration the sulfonating entity is H2S2O7, the σp+values of the OSO2Me and OSO2OMe substituents have been determined to be 0.40 and 0.46, respectively. The sulfonation of both 2‐chlorophenyl (10) and 2‐methylphenyl methanesulfonate (14) with 2.0 equiv of SO3in nitromethane at 0.0°C yields the 4‐sulfonic acid as the exclusive product, whereas 2‐methoxyphenyl methanesulfonate (13), under the same conditions, forms exclusively the 5‐sulfonic acid.2‐Chloro‐ (6), 2‐bromo‐ (7) and 2‐iodophenol (8) with 1.0 and 4.0 equiv of SO3in nitromethane yield exclusively the 4‐sulfonic acid, while 2‐fluorophenol (5) with 2.0 and 5.0 equiv of SO3yields in addition the 5‐sulfonic acid to the extent of 4 and 30%, respectively.In the reactions of 2,6‐dimethylphenol (15) and 2,6‐dimethylaniline (17) with at least 1 equiv of SO3in nitromethane, the 3‐SO3H/4‐SO3H ratio was found to increase on increasing the relative amount of SO3. For both15and17, the limiting 3‐SO3H/4‐SO3H ratio at high SO3/ArOH ratios is 86/14 and this value is considered to be the ratio for the sulfonation of both 2,6‐dimethylphenyl hydrogen sulfate and 2,6‐dimethylaniline‐N‐sulfonic acid. This assumption is supported by the observation that the sulfonation of 2,6‐dimethylphenyl methanesulfonate (16) andN‐(methylsulfonyl)‐2,6

ISSN:0165-0513    

DOI:10.1002/recl.19881071204

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe photochemistry of the diphenyl β,γ‐enones2and3and the methyl‐ and phenyl‐substituted α‐phenyl ketones4‐9has been studied, using mainly benzene as solvent. Irradiation of2with λ 300 nm leads to the 1,3‐acyl shift (1,3‐AS) product17, relatively small amounts of the decarbonylation products15and16, and the photo‐oxidation products benzophenone (18) and the α,β‐unsaturated aldehyde19. Direct irradiation of the 1,3‐AS product17yields15, 16, 18and19, but no2.Direct irradiation of 3 with λ 350 nm leads mainly to the formation of 1,3‐AS products (E)‐ and (Z)‐22, the decarbonylation products (E)‐ and (Z)‐20and21and, in addition, a small amount of thecis‐di‐π‐methane isomer23.Direct irradiation of the substituted α‐phenyl ketones4, 5, 8and9with γ 300 nm leads predominantly to the formation of the radical coupling products 2,3‐butanedione and24‐27, respectively, whereas6and7yield 1,2‐diphenyl‐1,2‐ethanedione and the respective24and25. The acetone‐sensitized irradiation of4leads to 4‐phenyl‐2‐butanon

ISSN:0165-0513    

DOI:10.1002/recl.19881071205

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19881071207

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19881071209

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19881071210

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19881071201

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY