摘要:

AbstractPhotolysis and Ag‐benzoate‐catalyzed decomposition of the diazo ketones2and4derived from Z‐Ala‐OH and Z‐Ala‐Ala‐OH in the presence of oligonucleotide derivatives bearing at the 5′‐terminus an NH2instead of the OH group, or an aminohexyl phosphate group lead to Z‐protected 3‐aminobutanoyl and to Z‐Ala‐β‐HAla derivatives, respectively (conjugates12,13, and17‐23,Schemes 3‐5), In solution, this amide‐forming acylation reaction could be realized only with oligomers containing up to 8 unprotected nucleotide building blocks (Schemes 3and4). With the analogous polymer‐bound and protected oligonucleotide derivatives as amino nucleophiles, excellent yields were obtained with all chain lengths tested (up to 15merScheme 5), The products were purified by reversed‐phase HPLC and characterized by MALDI‐TOF mass spectrometry (Figs. 2–4, Table 2) an

ISSN:0018-019X    

DOI:10.1002/hlca.19970800102

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

Configurational and Conformational Isomeric Antiaromatic [28]Tetraoxaporphyrinoids(4.2.4.2) and Aromatic [26]Tetraoxaporphyrin(4.2.4.2) Dications. A New Type of Molecular Dynamics in Macrocyclic SystemsThe [28]tetraoxaporphyrinoids(4.2.4.2)6are synthesized by cyclizingWittigreaction of (E, E)‐5, 5′‐(buta‐1, 3‐diene‐1, 4‐diyl)bis[furan‐2‐carbaldehyde] (8) with (E, E)‐{(buta‐1, 3‐diene‐diyl)bis[(furan‐5, 2‐diyl)methylene]}bis‐[triphenylphosphonium]dibromide (9) and 3, 3′‐{[(E)‐ethene‐1, 2‐diyl]bis(furan‐5, 2‐diyl)}bis[(E)‐prop‐2‐enal] (22) with (E)‐{(ethene‐1, 2‐diyl)bis[(furan‐5.2‐ diy)methylene]}bis[triphenylphosphonium]dibromide (23). An alternative path to get6is theMcMurrycondensation of8. Four different configurational isomers of6could be isolated and characterized by1H‐NMR spectroscopy. The (Z, EE, Z, EE)‐isomer6ais the first macrocyclic system where the inner and outer protons of the (E, E)‐dienediyl bridges exchange by rotation around the adjacent single bonds. In the (Z, EE, E, EE)‐isomer6b, the (E)‐ethenediyl bridge is rotationally active, while in the (E, ZE, E, EZ)‐isomer6cand in the (E, EZ, E, EZ)‐isomer6e, the rotation of both (E)‐ethenediyl bridges is observed. When in the dynamic systems the rotation of the active (E)‐double bonds at temperatures T<−90° is frozen, all configurational isomers of6appear to be antiaromatic and paratropic. The oxidation of the [28]tetraoxaporphyrinoids6cand6ewith DDQ yields the aromatic, diatropic [26]tetraoxaporphyrin(4.2.4.2) dications21e/21e′ both with (E, EZ, E, EZ)‐configuration but different fixed conformations. (Z, EE, Z, EE)‐Isomer6ais oxidized to give the (Z, EE, Z, EE)‐dication21a, while the oxidation of6byields a mixture of21aand21e/21e′. The standard formation enthalpies of the obtained and expected [28]tetraoxaporphyrinoids6and [26]tetraoxaporphyrin dications21hav

ISSN:0018-019X    

DOI:10.1002/hlca.19970800103

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractTwo new enantioselective syntheses of the naphthopyranquinone antibiotic frenolicin B (1), of its enantiomer2, and of its diastereoisomers3and4were accomplished using two different routes from optically active β‐Hydroxy esters (R)‐ and (S)‐11and18.β‐Hydroxy esters (R)‐ and (S)‐11were prepared stereoselectively from optically active sulfenylacetates (S)‐ and (R)‐10, respectively (Scheme 2, Method A). Alternatively, compound18was obtained in excellent yield by enantioselective hydrogenation of the corresponding β‐keto ester17, using a chiral ruthenium‐complex catalyst (Scheme 3, Method B). Subsequently, compounds (S)‐11and18were transformed into frenolicinB (1).In analogy, Stereoisomers2–4were prepared from (S)

ISSN:0018-019X    

DOI:10.1002/hlca.19970800104

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractAnomalous variations of one‐bond CC scalar coupling constants are observed in going from trinorbornane‐to trinorbornene‐like structures. Most notably, a 10‐Hz increase is observed in the coupling constant involving the C‐atoms of the ethano branch facing the CC bond. An effect of about half the size is characteristic of higher homologues (bicyclo[2.2.2]octenes), but no such effect is observed for monocyc

ISSN:0018-019X    

DOI:10.1002/hlca.19970800105

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractWe describe a versatile novel approach for the synthesis of 2, 4, 6‐trisubstituted pyrimidines on solid support. Thus, polymer‐boun J thiouronium salt2reacted in high yield in a cyclocondensation reaction with the acetylenic ketones3to form, aftertert‐butyl‐ester cleavage, the polymer‐bound carboxylic acids4, which were cleaved by oxidation with 3‐chloroperbenzoic acid and pyrrolidine to form the 2‐pyrrolidinylpyrimidine‐4‐carboxylic acids6a‐cin high yields and purities without further purification (Scheme 1). Alternatively, acid4awas subjected to anUgifour‐component condensation which gave the polymer‐boundUgiproducts9a‐ein good yields (Scheme 2). Multidirectional cleavage reaction of sulfone8awith different nucleophiles resulted in the clean formation of pyrimidine‐4‐carboxamides10–13(Scheme 3). This strategy combines efficiently solid‐phase chemistry with a multicomponent reaction and a multidirectional cleavage step to form highly divers

ISSN:0018-019X    

DOI:10.1002/hlca.19970800106

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe 2′‐deoxyisoguanosine phosphonates3aand4aand the phosphoramidites3band4bwere prepared as building blocks for solid‐phase oligonucleotide synthesis. The diphenylcarbamoyl (dpc) residue was introduced as 2‐oxo protecting group which stabilizes theN‐glycosylic bond against hydrolysis and prevents the molecule from side reactions. The dpc‐protected building blocks4a, bwere employed in solid‐phase synthesis and were found to be much more efficient than the unprotected compounds3a, b.Oligonucleotides with alternating (11) or consecutive isoguanine residues (13–15) were synthesized. They form duplexes with parallel chain orientation. The aggregate d(T4‐iG4‐T4) (15) containing four consecutive 2′‐deoxyisoguanosine is shown to be a tetramer similar

ISSN:0018-019X    

DOI:10.1002/hlca.19970800107

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe synthesis of three novel pyrazole‐containing complexing acids,N,N,N′,N′‐{2, 6‐bis[3‐(aminomethyl)pyrazol‐1‐yl]‐4‐methoxypyridine}tetrakis(acetic acid)(1),N,N,N′,N′‐{2, 6‐bis[3‐(aminomethyl)pyrazol‐1‐yl]pyrazine}‐tetrakis(acetic acid) (2), andN,N,N′,N′‐{6, 6′‐bis[3‐(aminomethyl)pyrazol‐1‐yl]‐2, 2′‐bipyridine}tetrakis(acetic acid) (3) is described. Ligands1–3formed stable complexes with EuIII, TbIII, SmIII, and DyIIIin H2O whose relative luminescence yields, triplet‐state energies, and emission decay lifetimes were measured. The number of H2O molecules in the first coordination sphere of the lanthanide ion were also determined. Comparison of data from the EuIIIand TbIIIcomplexes of1–3and those of the parent trisheterocycleN,N,N′,N′‐{2, 6‐bis[3‐(aminomethyl)pyrazol‐l‐yl]pyridine}tetrakis(acetic acid) showed that the modification of the pyridine ring for pyrazine or 2, 2′‐bipyridine strongly modify the luminescence properties of the complexes. MeO Substitution at C(4) of1maintain the excellent properties described for the parent compound and give an additional functional group th

ISSN:0018-019X    

DOI:10.1002/hlca.19970800108

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

Syntheses of New Phosphono Analogues of Pantetheine DerivativesThe phosphono analogues5and13of pantothenate 4′‐(dibenzyl phosphate) and pantetheine 4′‐(dibenzyl phosphate), respectively, are prepared as intermediates for the synthesis of a coenzyme‐A phosphono analogue (Schemes 1and2). The synthesis of phosphono analogues20and21of oxapantetheine, which are structurally similar compounds to the phosphono analogue of pantetheine, is also described (

ISSN:0018-019X    

DOI:10.1002/hlca.19970800109

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe first crystal structure of a molybdenum complex9with a hydrogenated pterinanda sulfur ligand contributes to the discussion about the active center of molybdenum and tungsten enzymes containing a molybdopterin cofactor. Complex9was synthesized through a redox reaction of [MoVIO2(LN‐S2)] (8; LN‐S2= pyridine‐2, 6‐bis(methanethiolato)) with 5, 6, 7, 8‐tetrahydropterin (7). 2 HCl (H4Ptr.2 HCl). The complex crystallizes, with a non‐coordinating Cl‐atom acting as a counterion, in the monoclinic space group C2/c (No. 15) with cell dimensionsa= 22.900(5),b= 10.716(2),c= 17.551(4) Å, β = 120.36(3)°, andZ= 8. We interpret9as [MoIVO(LN‐S2)(H+‐q‐H2Ptr)]Cl (q = quinonoid; H2Ptr = dihydropterin), i.e., a MoIVmonooxo center coordinated by a pyridine‐2, 6‐bis(methanethiolato) ligand and a protonated dihydropterin. The spectroscopic properties of this new complex are comparable to those of other crystalline molybdenum complexes of hydrogenated pterins without additional S‐coordination. The slightly H2O‐soluble complex9reacts with the natural enzyme substrate DMSO very slowly, possibly due to the lack of easily dissociab

ISSN:0018-019X    

DOI:10.1002/hlca.19970800110

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe syntheses of benzo‐fused benzo[2, 1‐b:3, 4‐b′]dithiophenes1and benzo[2, 1‐b:3, 4‐b′:5, 6‐c″]trithiophenes2are described. The treatment of easily available 3, 3′‐bis(phenylethynyl)‐2, 2′‐bithiophene derivatives5aand6(viaPdII‐catalyzed alkynylation of the corresponding 3, 3′‐dibromo‐2, 2′‐bithiophenes; seeScheme 1) with chlorotris‐(triphenylphosphine)rhodium(I) yields the corresponding cyclic rhodium complexes7(Scheme 2) which smoothly react with acetylenes and sulfur

ISSN:0018-019X    

DOI:10.1002/hlca.19970800111

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY