摘要:

AbstractRate constants and efficiencies of the oxidative bleaching of triplet‐excited methylene blue by different arene diazonium salts are determined by flash photolysis and stationary experiments.In the same way the rate constants of methylene blue photoreductions by diazabicylo[2,2,2]‐octane (DABCO), sodium tetraphenyl borate (TPB), sodium ethylenediamine tetraacetate (EDTA), and allyl thiourea (ATU) are determined.According to these results TPB reduces methylene blue photochemically not exceedingly fast (ke= 1.5 × 107M−1s−1) but with a high efficiency (η = 0.8).At high diazonium salt concentrations (10−1– 10−2M), the oxidation and the reduction mechanisms of the triplet‐methylene‐blue sensitized dediazoniation of arene diazonium salts have similar efficiencies at high as well as at low light intensities.At low diazonium salt concentrations and with diazonium salts of low reactivity, the reduction mechanism is favoured over the

ISSN:0021-8383    

DOI:10.1002/prac.19863280502

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

Synthesis and Reactivity of Estra‐1,3‐5(10)‐trienes with Heterocyclic Four‐Membered Rings in 14,15‐Position3‐Methoxy‐estra‐1,3,5(10),14‐tetraen‐17β‐ol acetate1and ‐17α‐ol acetate2react with chlorosulfonyl isocyanate in stereospecific manner and good yields to 3‐methoxy‐14β,15β‐[3′,4′‐(N‐chlorosulfonyl‐2′‐oxo‐azetidin)]‐estra‐1,3,5(10)‐trien‐17β‐ol acetate3and ‐17α‐ol acetate4, respectively. Hydrolysis of3and4in the presence of reducing agents affords the N‐unsubstituted oxo‐azetidines5and6, reduction of which gives the azetidines9and10. Cleavage of the azetidine ring yields the amino acid derivatives11and15, from which the oxooxetanes12and13and the hyd

ISSN:0021-8383    

DOI:10.1002/prac.19863280503

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

Partial Syntheses of Cardenolides and Cardenolide Analogues. X. Synthesis of 22‐O‐Substituted Cardenolides and Studies on the Oxidative Degradation of Cardenolides with Potassium PermanganateThe stereoisomeric 20,22‐dihydroxy‐cardanolides2aand3aas well as the oxalic acid half ester of the 3β‐acetoxy‐14,21‐dihydroxy‐5β,14β‐pregnan‐20‐one (4a) and 3β‐acetoxy‐20‐oxo‐5β,14β‐pregnane‐21,14‐lactone (5) were identified as intermediates of oxidative degradation of digitoxigenin 3‐acetate with potassium permanganate.2aand3a, after selective acylation in 22‐position, were converted to the 22‐acyloxy‐cardenolides7aand7bvia dehydration or acetoxyelimination after selective acetylation of the 20‐hydroxy group. Saponification of both7aand7byields the very stable 22‐hydroxy‐cardenolide8a.The molecular biological activities of the 22

ISSN:0021-8383    

DOI:10.1002/prac.19863280504

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

Partial Syntheses of Cardenolides and Cardenolide Analogues. XI. Synthesis of 3‐(3β,14‐Dihydroxy‐5β,14β‐androstan‐17β‐yl‐methyl)but‐2‐en‐4‐olide, a Homologous 5β,14β‐CardenolideWittig reaction of 3β,14‐dihydroxy‐5β,14β‐androstane‐17β‐carboxaldehyde4with 2‐carboxyl‐1‐ethoxycarbonyl‐ethyl‐triphenylphosphorane11followed by the reduction of the resulting half ester5and cyclization of the γ‐hydroxy acid6yields the 3‐alkylidenebutan‐4‐olide8awhich was isomerized to the 3‐(steroidylmethyl)but‐2‐en‐4‐olide9. Insertion of the methylene group between the steroidyl moiety and the but‐2‐en‐4‐olide ring strongly reduces the biological activity.Wegen der zentralen Bedeutung der relativen räumlichen Anordnung der 17β‐ständigen Seitenkette zum Steroidgerüst für die positiv inotrope Wirkung der Herzsteroide wurden in den vergangenen Jahren umfangreiche partialsynthetische Arbeiten zur Herstellung von Cardenoliden und Cardenolid‐Analogen mit dem Ziel einer veränderten geometrischen Anordnung des 17β‐ständigen Lactonringes durchgeführt. Die Arbeiten konzentrierten sich vor allem auf die Einführung von Substituenten mit dem Ziel einer veränderten konformationellen Anordnung des 17β‐ständigen Lactonringes [1‐6] sowie auf eine veränderte Verknüpfung des Butenolidringes in α‐Position (Actodigin) [7, 8]oder γ‐Position [9] (anstelle β‐Position bei den natürlich vorkommenden Cardenoliden) mit der 17β‐Position des Steroidgerüstes. Die molekularbiologische Struktur‐Wirkungsanalyse der bezeichneten Cardenolidderivate begünstigte den Schluß, daß für eine hohe Wirksamkeit der β‐verknüpfte, unsubstituierte But‐2‐en‐4‐olidring und die in den Cardenoliden vorliegende räumliche Beziehung zwischen Butenolid‐Seitenkette und Steroidgerüst erforderlich sind, durch die dann die komplementäre Geometrie von Seitenketten‐Bindungsschlucht und Steroid‐Bindungstasche (Erkennungsmatrix) im Rezeptorenzym, der (Na,K)‐aktivierten Adenosintriphosphat‐Phosphohydrolase (Na,K‐ATPase) des Herzmuskels [10, 11], definiert ist [12].Für die Analyse der Grenzen zwischen fixierter Geometrie und induzierter Anpassung der Erkennungsmatrix gewannen die homologen Cardenolide hervorragendes Interesse, bei denen die Lacton‐Seitenkette über eine Methylen‐ oder Methingruppe mit dem A/B‐cis‐ und C/D‐cis‐konfigurierten Steroidgerüst verknüpft ist und dadurch Bezüglich Abstand und Winkel zum Steroidgerüst stark von deren relativer Orientierung in den natürlich vorkommenden, hochwirksamen Cardenoliden abweicht. Das von Güntert et al. [13] synthetisierte 4′‐[(3β‐Hydroxy‐androst‐5‐en‐17β‐yl)methyl]‐2′(5′H)‐furanon, ein “17β‐homologes 3β‐Hydroxy‐card‐5,22‐dienolid”, ist für die Beantwortung dieser Fragestellung nicht geeignet; wegen der trans‐Verknüpfung anstelle der für eine Herzwirksamkeit zu fordernden cis‐Verknü

ISSN:0021-8383    

DOI:10.1002/prac.19863280505

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

ISSN:0021-8383    

DOI:10.1002/prac.19863280506

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

Abstract(R)‐ and (S)‐2,3‐dihydroxy‐3‐methylbutyl p‐toluenesulfonate, used as building blocks for vitamine D3metabolites and carotenoids, respectively, were resynthesized since differing melting points and optical rotations are reported in the literature. The given data of the (S)‐enantiomer could be corrected. A method for the determination of the enantiomeric purity was elaborated using the influence of a chiral lanthanide shift reagent on the1H‐n.m.r. spectra of these compounds. By this way it was shown that both compounds exhibit an enantiomeric excess of more than 94%. The (S)‐enantiomer was synthesized according to an improved synthetic scheme start

ISSN:0021-8383    

DOI:10.1002/prac.19863280507

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

Resolution and Absolute Configuration of the Enantiomers of cis‐6,6a,7,8,13,13a‐Hexahydro‐1‐benzopyrano[4,3‐b]‐1,5‐benzodiazepine DerivativesThe enantiomers of the cis‐6,6a,7,8,13,13a‐hexahydro‐1‐benzopyrano [4,3‐b]‐1,5‐benzodiazepine derivatives1–4have been obtained by resolution of their respective salts with (+)‐ or (−)1,1′‐bi‐2,2′‐naphthyl hydrogen phosphate. Their absolute configurations were assigned by X‐ray analysis of the hydrobromide of the (+)enantiomer3aand by subsequent comparison of its circular dichroism with those of the other enantiomers. Contrary to the high biological activity of the enantiomer3a, its antipode3bwas

ISSN:0021-8383    

DOI:10.1002/prac.19863280508

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractDeaminonicotianamine (8) and 2‐decarboxynicotianamine (11) were synthesized by stepwise reductive alkylation of (S)‐2‐ethoxycarbonylazetidine (3) or azetidine (9) with ethyl (S)‐4‐oxo‐2‐(trifluoroacetylamino)butanoate (4) and ethyl 4‐ oxobutanoate (7), respectively. The amino acids8or11as well as the intermediates, (2S,αS)‐α‐amino‐2‐carboxy‐1‐azetidinebutanoic acid (6) and (S)‐α‐amino‐1‐azetidinebutanoic acid (10) did not show biological activity with regard to chlorophyll synthesis in chlorotic leaflets of the tomato mutantchloronerva. The compound11promoted the normally inhibited root growth of the mutant.Nicotianamine (1) has been identified as the “normalizing factor” which restores chlorophyll synthesis, growth and development of the auxotroph mutantchloronervaofLycopersicon esculentumMill. [2]. Nicotianamine proved to be widespread in the plant kingdom ([1], cf. [3]). Biochemical experiments revealed a disturbed iron metabolism of the mutant, leading to an excessive iron absorption by the roots on the one hand and an irregular iron distribution within young leaves on the other [4, 5]. Nicotianamine (1) forms stable 1:1 complexes with iron (II) and other bivalent metal ions [6] with high stability constants in comparison with those of bidentate amino acids; e.g. the stability constants for the 1:1 copper complexes of nicotianamine and α‐alanine are 1018.6[6] and 108.5[7], respectively. As is evident from a Dreiding model, nicotianamine has an optimal molecular structure for complex formation with metal ions. Not only are six functional groups present, necessary for octahedral coordination, but the distances between the groups are also optimal for the formation of chelate rings: three 5‐membered rings formed by the α‐amino acid residues and two 6‐membered rings formed by the 1,3‐diaminopropane moieties [2, 3]. In order to study whether strong complex formation is important for the biological activity of nicotianamine, a series of synthetic analogues were prepared. The antipode of nicotianamine [8] and the proline analogue [9]were biologically active, further analogues, e.g. homologues with 1,4‐diaminobutane moieties [10], peptides [11]or quadridentate ligands [2, 8, 10] proved to be inactive. The hitherto existing results indicate that a partial structure2(or enantiomeric) is essential for the biological activity and that nicotianamine plays an important role in

ISSN:0021-8383    

DOI:10.1002/prac.19863280509

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

Synthesis of 5‐Nitro‐2,3‐dihydrobenzo(b)furanes from 2‐Methylenetriethyl‐ammonio‐4‐nitrophenolat and 2‐Chloro‐1,3‐dicarbonyl Compounds2,2‐Disubstituted 5‐nitro‐2,3‐dihydrobenzo[b]furanes6a–cwere synthezised in a one step procedure starting from 2‐methylene‐triethyl‐ammonio‐4‐nitrophenolat2and 2‐chloro‐1,3‐dicarbonyl compounds4a–c. The structure of6a–cwas de

ISSN:0021-8383    

DOI:10.1002/prac.19863280510

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractPhoto‐excited zinc phthalocyanine tetra(sulfomorpholide) (ZnPcTSM) sensitizes the dediazoniation of arene diazonium salts via electron transfer.1ZnPcTSM* reacts with p‐methyl‐, p‐methoxy‐, and p‐diethylamino benzenediazonium tetrafluoroborate, respectively, diffusion‐controlled,3ZnPcTSM* with rate constants 3.3 × 107, 8.5 × 107, and 1.1 × 108M−1s−1.Quantum yields of the dye bleaching by p‐methoxy benzenediazonium tetrafluoroborate show that the singlet reaction proceeds due to symmetry‐allowed back electron transfer with very low efficiency, whereas the triplet reaction reaches the ISC quantum yield at [ArN2⊕] ≈︁ 10−3M.In the triplet reaction an exciplex is formed as proved by the temperature dependence of the quenching rate constants and direct spectroscopic determination (τexciplex= 157 μs). From ΔG≠of the quenching reaction the solvation reorganization parameter λ0and the reaction

ISSN:0021-8383    

DOI:10.1002/prac.19863280511

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY