摘要:

AbstractThe two conformers of a cyclohexa‐2, 4‐dienone with different substituents at C(6) on irradiation are believed to undergo ring opening stereospecifically affording a mixture of two configurationally isomeric diene‐ketenes (and descendents thereof)‐ Exceptions are generally found for those dienones with one C and one O substituent or even with two C substituents, if one of them carries a polar group at a site able to interact through space with the ring CO group. In these cases, only one of the two anticipated diene‐ketenes (and descendents thereof) is produced. A thorough investigation of the photochemistry of a series of structurally different cyclohexa‐2, 4‐dienones on analytical as well as on preparative scale extends our mechanistic knowledge of the various routes from diene‐ketenes into a variety of compound classes. Novel compound classes accessible to diene‐ketenes are seven‐membered carbocycles (by intramolecular aldolization of the zwitterion of appropriately substituted, transiently formed diene‐(N, O)‐ketene acetals) and β‐la

ISSN:0018-019X    

DOI:10.1002/hlca.19970800602

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractDendritic iron porphyrins were synthesized as functional mimics of globular electron‐transfer heme proteins. The cascade molecules1 · Zn−3 Znof first to third generation were obtained starting from the (meso‐diarylporphyrin) zinc6 · Znwhich contains four carboxylate arms for attachment of the poly(ether‐amide) dendritic branches by peptide‐coupling methodology (Scheme 1). Generation 3 compound3 · Znwith 108 methyl‐carboxylate end groups has a molecular weight of 19054. D, and computer modeling suggests that its structure is globular and densely‐packed, measuringca.4 nm in diameter and, therefore, similar in dimensions to the electron‐transfer protein cytochrome‐c.Starting from the generation 1 poly(carboxylic acid)11 · Znand the generation 2 analog12 · Znthe dendritic ZnIIporphyrins4 · Znand5 · Zn, respectively, were obtained by esterification with triethyleneglycol monomethyl ether (Schemes 3and4). Demetallation followed by insertion of FeIIandin situoxidation afforded the water‐soluble dendritic iron porphyrins4 FeCland5 FeCl. The electrochemical behavior of esters1 · Zn−3 · Znin organic solvents changed smoothly with increasing dendritic generation (Table 1). Progressing from1 · Znto3 · Znin THF, the first porphyrin‐centered oxidation and reduction potentials become more negative by 320 and 210mV, respectively. These changes were attributed to strong microenvironmental effects imposed on the electroactive core by the densely packed dendritic surroundings. The electrochemical properties of4 · FeCland5 · FeClwere investigated by cyclic voltammetry in both CH2Cl2and H2O (Tables 2and3). Progressing from4 · FeClto5 · FeClin CH2Cl2, the redox potential of the biologically relevant FeIII/FeIIcouple remained virtually unchanged, whereas in aqueous solution,5 FeClexhibited a potential 420 mV more positive than did4 FeCl.The large difference between these potentials in H2O was attributed to differences in solvation of the core electrophore. Whereas the relatively open dendritic branches in4 · Fecldo not impede access of bulk solvent to the central core, the densely packed dendritic superstructure of5 · FeClsignificantly reduces contact between the heme and external solvent. As a result, the more charged FeIIIstate is destabilized relative to FeII, and the redox potential is s

ISSN:0018-019X    

DOI:10.1002/hlca.19970800603

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe title alkaloids were prepared from the common chiral precursor (−)‐(2S)‐2‐phenyl‐1, 5, 9‐triazacy‐clotridecan‐4‐one (4) which we had synthesized earlier. The spectral data for the spermidine macrocycles are in good agreement with the data reported for the isolated samples. Our experimental results indicate that the originally reported [α]Dvalue of −2.6 (c= 0.10, MeOH) for natural (S)‐viburnine is erroneous and should be + 17.0 (c= 0.92, MeOH). As a result of the chiroptical study conducted, it can be shown empirically that all alkaloids of the ‘celacinnine’ type

ISSN:0018-019X    

DOI:10.1002/hlca.19970800604

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe phosphoramidites6band9as well as the phosphonate6aderived from 7‐(hex‐1‐ynyl)‐ and 7‐[5‐(trifluoroacetamido)pent‐1‐ynyl]‐substituted 7‐deaza‐2′‐deoxyguanosines1and10, respectively, were prepared (Scheme 1). They were employed in solid‐phase oligodeoxynucleotide synthesis of the alternating octamers d(hxy7c7G‐C)4(12), d(C‐hxy7c7G)4(13), and d(npey7c7G‐C)4(15) as well as of other oligonucleotides (see22–25;Table 2; hxy = hex‐1‐ynyl, npey = 5‐aminopent‐1‐ynyl). TheTmvalues and the thermodynamic data of duplex formation were determined and correlated with the major‐groove modification of the DNA fragments. A hexynyl side chain introduced into the 7‐position of a 7‐deazaguanine residue (see1) was found to fit into the major groove without any protrusion. The incorporation of the (5‐aminopent‐1‐ynyl)‐modified 7‐deaza‐2′‐deoxyguanosine2into single‐stranded oligomers of the type24and25did not lead to change in duplex stability compared to the parent oligonucleotides. The self‐complementary oligomer15with alternating npey7c7Gd(2) and dC units did not lead to a cooperative melting, either due to orientational disorder or interaction of the 5‐aminopent‐1‐ynyl m

ISSN:0018-019X    

DOI:10.1002/hlca.19970800605

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractSubstituted dihydropyrazole‐spiro‐β‐lactams and isoxazolidine‐spiro‐β‐lactam derivatives are regio‐ and stereoselectively prepared by 1, 3‐cydoadditions between substituted α‐methylidene‐β‐lactams and diazomethane, nitrones, or thein‐situ‐prepared dipoles ‘diphenylnitrilimine’ and acetonitrile oxide. These reactions represent examples for 1, 3‐cycloadditions to the highly substituted, strained double bonds of α‐methylidene‐β‐lactams, and they need special experimental conditions as all reaction products are relatively unstable. Especially in solution, the reverse reaction is highly favoured. Regioselectivity and stereoselectivity of the reactions are elucidated mainly by NMR techniques

ISSN:0018-019X    

DOI:10.1002/hlca.19970800606

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe template condensation of [Cu(3, 2, 3‐tet)]2+(3, 2, 3‐tet =N,N″)‐(ethane‐1, 2‐diyl)propane‐1, 3‐diamine with CH2O and en (en = ethane‐1, 2‐diamine) affords the copper(II) compounds of two isomeric tricyclic ligands in high yield. The strikingly different UV/VIS and EPR spectroscopic behavior of these two compounds, [Cu(‘syn’‐L)](CIO4)2and [Cu(‘anti’‐L)](ClO4)2· 1/2 H2O (L = 1, 4, 8, 10, 13, 15‐hexaazatricyclo [13.3.1.14, 8]icosane), is analyzed by angular overlap model (AOM) calculations based on the experimentally determined solid‐state structures (powder spectra) and a combination of molecular mechanics and AOM calculations (MM‐AO

ISSN:0018-019X    

DOI:10.1002/hlca.19970800607

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe determination of the chemical structure of a previously unknownMaillardreaction product with an amino acid incorporated in a four‐ring structure is reported. The red compounds1aand1b, isolated from a thermally treated aqueous solution of furan‐2‐carbaldehyde and L‐alanine, were identified as (S)‐4{(E)‐1‐formyl ‐2‐(2‐furyl)ethenyl}‐5‐(2‐furyl)‐2‐{(E)‐(2‐furyl)methylidene}‐2, 3‐dihydro‐α‐methyl‐3‐oxo‐1H‐pyrrole‐1‐acetic acid and its 2‐{(Z)‐(2‐furyl)methylidene}isomer, respectively, by several 1D‐ and 2D‐NMR techniques, MS, UV, and IR spectroscopy as well as by synthetic experiments. 2D‐NOESY and 2D‐ROESY experiments performed f

ISSN:0018-019X    

DOI:10.1002/hlca.19970800608

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractKhusimone (1), one of the main odor‐donating compounds of vetiver oil, is subject of the following study on structure/odor relationship. Ring opening of the carbonyl‐functionalized bridge of the tricyclic khusimone leads to the bicyclic structures2a/b. The enantioselective approach to these degraded structures is described, and the olfactory consequences are studied. Starting point of the synthesis is an enantiomerically pure enone ester which is easily obtainable from camphorsulfonic a

ISSN:0018-019X    

DOI:10.1002/hlca.19970800609

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractIrradiation (λ = 350 nm) of 1H‐[2]benzothiopyran‐1‐one (2) in the solid state affords selectively and in good yield 6aα, 6bα, 12bα, 12cα ‐tetrahydrocyclobuta[1, 2‐c:4, 3‐c′]bis([2]benzothiopyran)‐5, 8‐dione (3), the head‐to‐head (HH)cis‐cisoid‐cis‐cyclodimer of2, X‐Ray analysis of2confirms that this reaction proceeds according to the well‐established topochemical principles. The same dimer3is obtained in low yields on irradiation of 10−1Msolutions of2in either MeOH or MeCN, while no conversion at all is observed in benzene. On irradiation of2in MeCN in the presence of tetrachloroethene, the [2 + 2] photocycloadduct4is formed in good yield, the conversion2 → 4being efficiently quenched by naphthalene. In contrast, no reaction is observed ‐on irradiation of2in the presence of 2, 3‐dimethylbut‐

ISSN:0018-019X    

DOI:10.1002/hlca.19970800610

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractVarious condensed areno[g]lumazine derivatives2,3, and5–7were synthesized as new fluorescent aglycones for glycosylation reactions with 2‐deoxy‐3, 5‐di‐O‐(p‐toluoyl)‐α/β‐D‐erythro‐pentofuranosyl chloride (10) to form, in aHilbert‐Johnson‐Birkoferreaction, the correspondingN1‐(2′‐deoxyribonucleosides)15–21. The β‐D‐anomers15,17,19, and21were deblocked to24–27and, together withN1‐(2′‐deoxy‐β‐D‐ribofuranosyl)lumazine (22) and its 6, 7‐diphenyl derivative23, dimethoxytritylated in 5′‐position to28–33.These intermediates were then converted into the 3′‐(2‐cyanoethyI diisopropylphosphoramidites)34–39which function as monomeric building block in oligonucleotide syntheses as well as into the 3′‐(hydrogen succinates)40–45which can be used for coupling with the solid‐support material. A series of lumazine‐modified oligonucleotides were synthesized and the influence of the new nucleobases on the stability of duplex formation studied by measuring theTmvalues in comparison to model sequences. A substantial increase in theTmis observed on introduction of areno[g]lumazine moieties in the oligonucleotide chain stabilizing obviously the helical structures by improved stacking effects. Stabil

ISSN:0018-019X    

DOI:10.1002/hlca.19970800611

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY