摘要:

AbstractIn the molecular biology of eukaryotic organisms, the elucidation of mechanisms involved in the regulation of gene expression has assumed an important role. All cells of an organism carry the same genes, but differ in the patterns of genes they express. There is an increasing amount of evidence that cancer cells exhibit a pattern of gene expression which can be very different from that of normal cells. One of the molecular signals that has been recognized in the regulation of gene expression in eukaryotes is the modified nucleotide 5‐methylcytosine (5‐mC). Through experiments in well‐characterized eukaryotic systems, evidence has been adduced that the introduction of 5‐mC into highly specific sequences, particularly into the 5′ and promoter regions of a gene, can cause gene inactivation. Viral and other eukaryotic systems have helped in the recognition of this cause‐and‐effect relationship. Inactive genes are frequently hypermethylated in the promoter region; active genes are hypomethylated. However, these correlations are not always as simple and straightforward. The biochemical mechanisms by which site‐specific DNA methylations cause gene inactivation have not yet been determined. It is plausible to postulate that promoter methylations could somehow affect the binding of cellular enzymes involved in recognizing the promoter of a gene. Structural alterations of DNA promoter sequences arising from DNA methylations could also be important. DNA methylation is likely to represent a long‐term inactivation signal, since it is presently thought that patterns of DNA methylation can be changed only by DNA replication and specific inhibition of post‐replicative main

ISSN:0570-0833    

DOI:10.1002/anie.198409193

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY

摘要:

AbstractEven today, there are conspicuous gaps in the register of organic synthetic methods. Thus, numerous types of homoenolate reagents are listed; yet no generally applicable method for the homologue of the aldol addition, viz. the homoaldol addition, is to be found. The methods documented up to 1980 offer only singular solutions, and, moreover, are not stereoselective. The present article gives an overview of the existing possibilities and then describes how the gap can be closed by using a new class of homoenolate reagents: 2‐alkenyl esters ofN,N‐diisopropylcarbamic acid are lithiated and the resulting allyllithium compounds tailored to high regio‐ and diastereoselectivity in addition reactions to the carbonyl group via metal exchange. Altogether, the homoaldol reactions now offer a general and reliable, highly stereoselective entry to γ‐hydroxycarbonyl compounds, whereby the C(β)C(γ) bond is formed. Furthermore, it is demonstrated how problems associated with the application of allyl anions as synthetic reagents can be

ISSN:0570-0833    

DOI:10.1002/anie.198409321

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY

摘要:

AbstractDendralenes are acyclic and cyclic cross‐conjugated polyolefins derived from 3‐methylene‐1,4‐pentadiene. This review summarizes and compares, for the first time, the methods developed for the synthesis of this class of hydrocarbons. Because of their particular arrangement of π‐electrons, the dendralenes are novel substrates for addition and rearrangement reactions, and model compounds for spectroscop

ISSN:0570-0833    

DOI:10.1002/anie.198409481

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198409601

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198409611

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198409631

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198409651

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198409661

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198409681

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY

ISSN:0570-0833    

DOI:10.1002/anie.198409691

出版商:Hüthig&Wepf Verlag    

年代:1984

数据来源: WILEY