摘要:

AbstractFour peri‐substituted naphthalene‐1‐diazonium cations all show short attractive interactions between an electron‐rich atom of the peri‐substituent and the α ‐N‐atom of the diazonium group. These are interpreted as models for incipient nucleophilic attack on a NN bond. The diazonium group is a better acceptor of electron density ‘through space’ than the NO2group, which parallels their relative ‘through‐

ISSN:0018-019X    

DOI:10.1002/hlca.19930760402

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractUV/VIS Absorption spectra of nitrosubsituted (o‐hydroxyphenyl)methylphosphonic acids (o‐(phosphonomethyl)phenols) were measured as a function of pH at 25° in 0.1MNaClo4solutions. Computational treatment of the whole set of optical density data between 200 and 500 nm resulted in the determination of the dissociation constants of these polyacids and also of the individual electronic spectra of all the species involved in the deprotonation sequence. The spectral behavior gives information on the structure of the anions formed and consequently the order of the subsequent deprotonation steps could be deduced. For the (2‐hydroxy‐3‐nitro(or 5‐nitro)phenyl)methylphosphonic acid and the 2‐hydroxy‐5‐nitro‐1,3‐phenylenebis(methylphosphonic acid), the phenolic proton dissociates in the last step, while, in the case of (2‐hydroxy‐3,5‐dinitrophenyl)methylphosphonic acid, the last dissociating proton comes from a POH group. An intermediate situation is found for (3‐chloro‐2‐hydroxy‐5‐nitrophenyl)methylphosphonic acid. Generally, the deprotonation sequence is governed by intramolecular

ISSN:0018-019X    

DOI:10.1002/hlca.19930760403

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractBuilding blocks derived from 7‐deazaguanosine (c7G,1) were prepared for solid‐phase oligoribonucleotide synthesis. Compound1was converted into the isobutyurl derivative2band the (dimethylamino)methylidene compound3(Scheme 1). After tritylation (→4a,b), silylation was studied with regard to regioselectivity. It was found that the triisopropylsilyl group in combination with the (dimethylamino)methylidene residue gave the highest 2′ ‐selectivity (→5e). The 2′ ‐O‐silyl derivative5ewas reacted with PCl3affording the 3′ ‐phosphonate7which was used in solid‐phase oligoribonucleotide synthesis. Oligonucleotides derived from U‐G‐G‐G‐G‐U with an increasing number of c7G residues instead of G were synthesized. Aggregation was studied by polyacrylamidegel electrophoresis and CD Spectroscopy. Disaggregation of the G4‐structure of U‐G‐G‐G‐G‐U was observed when c7G replaced G, demonstrating that guanine

ISSN:0018-019X    

DOI:10.1002/hlca.19930760404

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe glycosylation of the 4‐methoxypyrazolo[3,4‐d]pyrimidine (5) anion with 1‐halo‐2‐deoxyribose6in MeCN/TDA‐1 givesN2‐deoxynucleoside9(29%) together withN1‐isomer7(48%) and its anomer8(6%) [7]. The α‐D‐anomer8is not formed and the yield of the ß‐D‐anomer7increased to 62% when dimethoyethane is used as solvent and [18]crown‐6 as catalyst. Employing 1‐halo‐2,3‐dideoxyribose10instead of halogenose6, the 2′,3′ ‐didexoynucleosides12and14were formed which desilylated (→1band2b) and converted into the ddI and ddA derivatives3b(c7z8Idd),15b(c7z8Add), and17(c7z8A′dd). Contrary to 7‐deazapurine nucleotides, the triphosphates of3band15bshowed on appreciab

ISSN:0018-019X    

DOI:10.1002/hlca.19930760405

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe catalytic hydrogenation of rifamycinS(2) over Pd/C, followed by oxidation with K3[Fe(CN)6], generates a pair of 16,17,18,19‐tetrahydrorifamycinsS(3/4), epimeric atC(16). The use of PtO2as catalyst leads to the hydrogenation also of the C(28)C(29) bond giving, after oxidation by K3[Fe(CN)6], a mixture of the epimers (16R)‐ and (16S)‐16,17,18,19,28,29‐hexahydrorifamycinsS(5/6). Furthermore, we synthesized the (16R)‐ and (16S)‐3‐bromo derivatives7/8and (16R)‐ and (16S)‐3‐(piperidin‐1‐yl) derivatives9/10. The determination of the X‐ray crystal structure of the most abundant epimer4of the tetrahydrorifamycins allowed the assignment of the absolute configuration at C(16) of all derivative. A Structure‐activity relationship study showed that in general the (16R)‐epimers are more potent inhibitors of bacterial RNA po

ISSN:0018-019X    

DOI:10.1002/hlca.19930760406

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

Acid‐Catalyzed Reactions of 2‐Vinylaniline Derivatives with 1‐Benzyl‐ and 1‐Methylpiperidin‐4‐one: An Elegant Synthesis of New Polycyclic Indole DerivativesThe reaction of 2‐vinylaniline derivatives with 1‐benzylpiperidin‐4‐one or 1‐methylpiperidin‐4‐one in toluene at temperatures between 115 and 120° with toluene‐4‐sulfonic acid as catalyst leads in good yields to a new class of polycyclic indole derivatives (Scheme 1, Table 1). The structure of the new diastereoisomerically pure racemic compounds1–5is determined by NMR‐spectroscopic methods. A reaction mechanism proceedingviacyclization of enamine9, leading to a racemic, tricyclic reactive intermediate10, and subsequent intramolecular 1,5‐dipolar cyclization as key steps in proposed for the formation of octahydropyrido[4′,3′:4]cyclobut[1,2‐b]indoles1–5. The scope and limitation

ISSN:0018-019X    

DOI:10.1002/hlca.19930760407

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractX‐Ray Crystal‐structure analysis of 2,4,8,10‐tetrakis(1,1‐dimethylethyl)‐6,6‐dimethyl‐12H‐dibenzo[d,g][1,3,2]‐dioxasilocin showed that its eight‐membered organosilicon heterocycle adopts a boat‐boat (BB) conformation in the solid

ISSN:0018-019X    

DOI:10.1002/hlca.19930760408

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractFive New unusual monoterpene‐substituted dihydrochalcones, the adunctins A–E (1″S)‐1‐{2′‐hydroxy‐4′‐methoxy‐6′‐[4″‐methyl‐1″‐(1‴‐methylethyl)cyclohex‐3″ ‐en‐1″ ‐yloxy]phenyl}‐3‐phenylpropan‐1‐one (1), (5aR*,8R*,9aR*)‐3‐phenyl‐1‐[5′,8′,9′,9′a‐tetrahydro‐3′‐hydroxy‐1′‐methoxy‐8′‐(1″‐methylethyl)‐5′‐a‐methyldibenzo‐[b,d]furan‐4′‐yl]propan‐1‐one (2), (2′R*,4″S*)‐1‐{6′‐hydroxy‐4′‐methoxy‐4″‐(1‴‐methylethyl)spiro[benzo[b]‐furan‐2′(3′H),1″ ‐cyclohex‐2″ ‐en]‐7′‐yl}‐3‐phenylpropan‐1‐one (3), (2′R*,4″R*)‐1‐{6′‐hydroxy‐4′‐methylethyl‐4″‐(1‴‐methylethyl)spiro[benzo[b]furan‐2′(3′H),1″‐cyclohex‐2″‐en]‐7′‐yl}‐3‐phenypropan‐1‐one (4), and (5′aR*,6′S*, 9′R*,9′aS*)‐1‐[5′a,6′,7′,8′,9′a‐hexahydro‐3′,6′‐methoxy‐6′‐methyl‐9′‐(1″‐methylethyl)dibenzo[b,d]‐furan‐4′‐yl]‐3‐phenylpropan‐1‐one (5) were isolated from the leaves ofPiper aduncum(Piperaceae) by preparative liquid chromatography. In addition, (−)‐methyllindaretin (6),trans

ISSN:0018-019X    

DOI:10.1002/hlca.19930760409

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractReported here are the novel free porphyrins corallistin B, C, D, and E, isolated as methyl esters2a,3a,4a, and5a, respectively, from the spongeCorallistessp. (Lithistida) collected at the basis of the south New Caledonian coral reef. A protocol is also established for formylation of their NiIIcomplexes, which show a different reactivity pattern toward DMF/POCl3 from metal complexes of deuteroporphyrins. Together with corallistin A, Previously isolated as the methyl ester1a, and the known deuteroporphyrin IX (isolated as6a) also present in the sponge, the new corallistins, which may be thought to derive from protoporphyrinviaheme, account for an amazing 60% of the EtOh extract from the sponge.

ISSN:0018-019X    

DOI:10.1002/hlca.19930760410

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractCucl2‐Induced oxidative coupling of 2‐(tert‐butyl)‐6,6‐dimethylpentafulvenyl anion9predominantly takes place at C(7) and C(5) to give [7–7] and [7–5]coupling products15and16in 35 and 47% yields, respectively (Scheme 3) whose structures are elucidated from 1D‐ and 2D‐NMR analysis. Compared with the product distribution observed for 6,6‐dimethylpentafulvenyl anion2(Scheme 1), no coupling at C(2)/C(3) of9is observed. This means that, besides electronic effects, steric effect are also important in oxidative couplings of fulvenyl anions. The same couplings occur in the case of 2,3‐bis(6,6‐dimethylfulven‐2‐yl)‐2,3‐dimethylbutane dianion10as well but, due to electronic as well as conformational effects (Scheme 5), intermolecular coupling (to give polymers17,Scheme 4) is strongly favored over intermolecular coupling. Mechanisms explaining base‐catalyzed isomerization15a⇄15b⇄15c(Scheme 6) as well as isomer

ISSN:0018-019X    

DOI:10.1002/hlca.19930760411

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY