摘要:

AbstractThe chemistry of zirconium(III) is comprehensively reviewed (95 references) up to April 1988 with emphasis being placed on synthetic methods and structural features.

ISSN:0165-0513    

DOI:10.1002/recl.19891080102

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractThe sulfation and sulfonation resulting from the reaction of the dihydroxybenzenes and their mono‐ and dimethyl ethers with SO3in nitromethane have been studied, and their product distributions are reported. As to the non‐hydroxy‐substituent‐containing substrates, 1,2‐dimethoxy‐benzene (3) yields the4‐sulfonic acid (3‐4‐S) which, upon further sulfonation, yields a 1:4 mixture of the 3,5‐ and 4,5‐S2. The 1,3‐ (6) and 1,4‐isomer (9) yield initially the 4‐ and 2‐S, respectively, and subsequently exclusively6‐4,6‐ and9‐2,5‐S2, respectively.With the substrates containing one hydroxy substituent, the sulfonation isomer distribution is dependent on the SO3to substrate ratio if the OH and OMe substituents are inorthoorparaorientation, due to increasing sulfonation of the corresponding methoxyphenyl hydrogen sulfate. Thus, 2‐methoxy‐ (2) and 4‐methoxyphenol (8) with one equiv of SO3at 0°C yield a 3:1 mixture of2‐4‐S and2‐5‐S and a 9:1 mixture of8‐2‐S and8‐3‐S, respectively, but, with ≥4 equiv of SO3, the former reactant yields only2‐5‐S and the latter only8‐3‐S. 3‐Methoxyphenol (5) yields initially a 1:1 mixture of the 4‐ and 6‐sulfonic acid. Further sulfonation yields only5‐O,4,6‐S3which slowly cyclizes to the 1,3,2,4‐benzodioxadithiin 2,2,4,4‐tetraoxide derivative11.As to the dihydroxy‐containing substrates, 1,2‐dihydroxybenzene (1) with 1 equiv of SO3first yields the hydrogen sulfate 1‐O‐S which rearranges to1‐4‐S; on using an excess of SO3, the eventual product isl‐O(2),4‐S2. Similarly, the 1,4‐isomer (7) with 1 equiv of SO3yields initially7‐O‐S which isomerizes to7‐2‐S. With 6 equiv of SO3, initially7‐O,O‐S2is formed and subsequently its 2‐sulfonic acid, which eventually cyclizes slowly to the 1,3,2,4‐benzodioxadithiin 2,2,4,4‐tetraoxide derivative12. The 1,3‐isomer4with 1 equiv of SO3yields the 4‐sulfonic acid. With 4 equiv of SO3, initially4‐O,O‐S2is formed and subsequently4‐4,O,O‐S3, which is converted in

ISSN:0165-0513    

DOI:10.1002/recl.19891080103

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractReaction of galactitol in dimethyl sulphoxide, with 2,2,‐dimethoxypropane‐pyridiniump‐toluenesulphonate has led to the isolation of some new isopropylidene acetals. Their structures have been established spectroscopically. Attempts have been made to assess their possible role in the conventional acid‐catalysed isopropylidenation of this

ISSN:0165-0513    

DOI:10.1002/recl.19891080104

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractIn order to obtain a light‐stable rhodopsin as a potential candidate for crystallization and structural X‐ray analysis, we synthesized and characterized the novel allE‐10,20‐methano‐retinoyl fluoride (2). This retinal analogue has a locked 11‐cisconfiguration, preventing the light‐induced 11‐cis→transisomerization and binds to opsin by a stable peptide bond rather than a Schiff base.2reacted with (methylated) bovine opsin, forming a light‐ and thermo‐stable pigment with λmaxat 390 nm. Its opsin shift (2500 cm−1) is in the same order of magnitude as that in rhodopsin (2650 cm−1), suggesting that the mechanism for the red shift is not located in the direct vicinity of the chromophore‐protein linkage. We also report the first synthesis and characterization of all‐E‐retinoyl fluoride (10), which failed to give a pigme

ISSN:0165-0513    

DOI:10.1002/recl.19891080105

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

AbstractDuplex stabilities have been determined for several hybrids of phosphate‐methylated oligonucleotides and natural DNA or RNA using UV hyperchromicity experiments. These hybrids have a higher stability than the corresponding natural duplexes, due to the absence of interstrand electrostatic repulsions. Comparison with stability data for hybrids of other neutral oligonucleotides (with phosphate‐ethylated and methyl phosphonate linkages) and natural DNA or RNA revealed that differences in stability could be attributed mainly to steric and stereoelectronic factors. For phosphate‐ethylated oligonucleotides, hybridization with a natural strand is strongly influenced by steric interactions of the ethyl group. Hybridization with RNA, which requires a tight A‐type conformation, is therefore difficult and the ethyl orientation (inward or outward, depending on the phosphorus configuration) determines the strength of the association with natural DNA. In methyl phosphonate systems, it appears that the presence of a PC bond disturbs the helix conformation for stereoelectronic reasons. This leads to a weaker hybridization with DNA and RNA for longer strands. Phosphate‐methylated oligonucleotides are found to have an optimal combination of steric and stereoelectronic factors and form the strongest hybrids with natural DNA. Absence of intrastrand phosphate‐phosphate repulsions causes a slightly different conformation for phosphate‐methylated DNA, which is evident in the cooperative character of the hybridization with natural DNA. A thermodynamic model for this cooperativity is presented and the model studies are extended to protein‐DNA complexes in which phosphate charges are also shielded. The preliminary results suggest that protein association can destabilize a DNA duplex, thus providing a possible mechanism for the action of DNA

ISSN:0165-0513    

DOI:10.1002/recl.19891080106

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

摘要:

Abstract1‐(Hydroxyimino)‐3‐aryl‐1,2,3,4‐tetrahydronaphthalenes, when subjected to Semmler‐Wolff reaction using Beckmann's mixture, give hitherto unknown 3‐aryl‐1‐naphthalenamines, which have been characterised using elemental analyses

ISSN:0165-0513    

DOI:10.1002/recl.19891080107

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19891080109

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19891080101

出版商:WILEY‐VCH Verlag    

年代:1989

数据来源: WILEY