摘要:

AbstractThis review describes our preliminary results of ring enlargement ofN‐heterocycles byN‐ylide formation at a targeted site, exemplified by 55→56→58. Before development of this method, the strategy can be traced to our modified Hofmann degradation led at first to several miscarried probings on the reaction betweenN‐halomethyl ammonium salts and halophilic

ISSN:0009-4536    

DOI:10.1002/jccs.199500081

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractNew YBnXscales of solvent ionizing power are developed and considered superior to Yxscales for benzylic bromides, chlorides,p‐nitrobenzoates and tosylates in Grunwald‐Winstein type correlation analysis of solvolytic reactivities. The YBnXvalues, with addition and revision, are summarized. Evidence for nucleophilic solvent intervention in the solvolysis transition state for secondary and tertiary benzylic substrates is given. The advantages of employing this tool to understand solvolysis mechanisms are discus

ISSN:0009-4536    

DOI:10.1002/jccs.199500082

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractFollowing the discovery of salicylates and its conversion to aspirin, natural products research has provided many promising leads for further modification as anti‐inflammatory and analgesic agents. Recent studies have focused on biosynthesis inhibitors of eicosanoids and receptor antagonists of the platelet activating factor, including a new class of dual functional inhibitors derived from neolignans. The highly potent analgesic alkaloid epibatidine from the frog skin has been synthesized and recharacterized as a very strong acetylcholine nicotinic receptor agonist. Some novel epibatidine analogs have shown promise as potential CNS drugs and research probes for clarifying the anti‐addictive property of the African alkaloid iboga

ISSN:0009-4536    

DOI:10.1002/jccs.199500083

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractRecent developments in research on aggregation and self‐coiling of organic molecules are reviewed: structure and medium effects on aggregating tendencies, electrostatically stabilized aggregates (ESAg), co‐aggregating tendencies of cholesterols and the effect of chain‐folding, and neutral and effective deaggregators (d

ISSN:0009-4536    

DOI:10.1002/jccs.199500084

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractDeoxy sugars are ubiquitous in nature and contribute to diverse biological activities. Attempts to design systems to control or to mimic their functions are hampered, however, by the lack of biosynthetic knowledge of these unique sugars. To elucidate the mechanism by which the sugar deoxygenation is effected, we have initiated a study to explore the biosynthesis of CDP‐ascarylose, a 3,6‐dideoxyhexose found in the lipopolysaccharides ofYersinia pseudotuberculosis, and our initial focus centered on C‐3 deoxygenation catalyzed by E1and E3. We have now purified the wild‐type enzymes, cloned the corresponding genes (ascC for E1andascD for E3), and overexpressed the gene products inEscherichia coli.The purified E3is a flavoprotein comprising an iron‐sulfur center and E1is an iron‐sulfur containing, pyridoxamine 5′‐phosphate‐de‐pendent enzyme. Since these iron‐sulfur clusters are well known one‐electron carriers, reactions mediated by E1and E3must proceed via a radical mechanism. Recently, EPR analysis of E1/E3catalysis indicated a potential new redox role for pyridoxamine as a cofactor. These findings make this system unique from two perspectives: E1is the only coenzyme B6‐dependent catalyst that interacts with a sugar and not with an amino acid, and it is the first example in which coenzyme B6may facilitate one‐electron redox chemistry. Thus, the unprecedented mechanisms of E1and E3distinguish this system as a novel radical deoxygenation with potentially inte

ISSN:0009-4536    

DOI:10.1002/jccs.199500085

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractIntramolecular cyclization of α‐carbonyl radicals to the trimethylsilylacetylenic side chain gives bicyclic vinylsilane ketones and enones. Application of this cyclization to total synthesis of (±)‐modhephene is desc

ISSN:0009-4536    

DOI:10.1002/jccs.199500086

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractA series of artificial photosynthesis porphyrin compounds consisting of electron donor and electron acceptor (compounds 1‐6) were synthesized. Their spectroscopic behaviors in solution were investigated and the synthetic molecular devices were prepared with these molecules by using LB technique. It was indicated that multistep electron transfer and charge separation for these compounds actually occur, which is of great advantage to their photoelectric conversion. An efficient energy transfer process takes place for compound 6. A mechanism involving photoinduced electron transfer and multistep charge separation for these compounds was suggested. With only one monolayer of tetrad 1 LB film on the surface of Sn02conductive glass, high photo‐driven voltage and current were obtai

ISSN:0009-4536    

DOI:10.1002/jccs.199500087

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractAnnelation or substitution of the (1,4)‐bridged ring of [22](1,3)(1,4)cyclophane4, such as in8and9, respectively, result in two different conformational ground states in each case. Each conformational ground state involves a different destabilizing factor arising from one form of non‐bonding interaction. Only the conformers8band9bwere isolated experimentally. Their corresponding precursors11and23were also found to be conformationally rigid. Only the conformers11aand23awere isolated indicating an abrupt change in conformational preference going from the dithia[32]cyclophanes to the respective [22]cyclophanes. The selectively methylated [22]cyclophanes27,31and32were, however, found to be conformationally mobile. There is an increase of about 10–15 kJ mol−1in conformational energy barrier going from4to27or31. This is consistent with the fact that the presence of the methyl substituents increases the relative conformational ground‐state energy more than it would affect the transition‐state energy. The conformational barrier of32was unexpectedly found to be similar to those of27and31. This could be explained by a decrease in the transition‐state energy due to an inward bending of the (1,4)‐bridged ring accompanied by a decrease in conformational ground‐state energy due to an outward bending of the m

ISSN:0009-4536    

DOI:10.1002/jccs.199500088

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractMonomolecular films with well‐defined structure were prepared by self‐assembling of n‐alkanoic acids on an evaporated silver surface. Here we report the structural studies of thin films of acids containing aromatic chromophores of varied size and polarity. Information regarding the packing, orientation and conformation of the structural units within the assembly were deduced from ellipsometric thickness measurement, polarized reflection absorption infrared spectra and wetting property measurement. Implications of results to the design of functional thin films are disc

ISSN:0009-4536    

DOI:10.1002/jccs.199500089

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY

摘要:

AbstractFour oligonucleotides (15 mer)13–16and their conjugates17–20in which psoralen was covalently linked to 5′ end were synthesized. Compounds16and20contain the sequence which is complementary to the sense strand covering the first four codons and the upstream sequence close to the ribosome binding site of c‐Ha‐rasmRNA. It was found that compounds16and20inhibited the growth of cells that had been transformed by the c‐Ha‐rasplasmid activated c‐Ha‐rasoncogene. Compound20that carried psoralen was more efficient in inhibiting the growth of transformed cells than compound16without psoralen, suggesting that the psoralen might have increased permeability of oligodeoxynucleotides. A model experiment of duplex formation was pertinent to the idea that the inhibitory effect was caused by

ISSN:0009-4536    

DOI:10.1002/jccs.199500090

出版商:WILEY‐VCH Verlag    

年代:1995

数据来源: WILEY