摘要:

AbstractBiphenylene dianion has been prepared by Li reduction of the parent hydrocarbon. It is stable below −30° and was characterized by its1H‐ and13C‐NMR spectra. A comparison of these data with those of the dication indicates the existence of ion pairs in the dianion case which are responsible for a different charge distribution. The diamagnetic ring currents of both ions, however, are of comparable magnitude, and both are more diatropic than the parent hydrocarbon. Predictions of the π‐charge‐density effect on1H chemical shifts are improved by calculations that use the linear and quadratic electric‐field effect equation instead of the simpleSpiesecke‐Sc

ISSN:0018-019X    

DOI:10.1002/hlca.19860690502

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractThe electronic structure of [4.2.2]propella‐2,4,7,9‐tetraene (1), 2,5‐etheno[4.2.2]propella‐3,7,9‐triene (2), and of several hydrogenated derivatives of2has been investigated using He(I) PE spectroscopy and MO calculations. It is found that in2the 1,4‐cyclohexadiene moiety interacts considerably with the bicyclo[2.2.0]hexadiene unit, while in1the interaction between the butadiene fragment and theDewarbenzene unit is minute. The syntheses of3–

ISSN:0018-019X    

DOI:10.1002/hlca.19860690503

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

Novel Diterpenoids from Leaf Glands ofPlectranthus barbatus(Labiatae). The Absolute Configuration of the 2‐Hydroxypropyl Group in Coleon EIn addition to the previously reported quinone methides coleon E (1a), coleon F (2a) and the spirocoleon9(plectrin), novel rearranged abietanoid dienediones, called (16R)‐plectrinon A (3a) and plectrinon B (5) as well as the allylroyleanone8ahave been isolated fromPlectranthus barbatusand their structures elucidated mainly by spectroscopy. Closer investigation of acetylations of1aand2aestablished the hitherto unknown structures1c,2c,3b,10a,10b,11a,11b,12a, and12b. The derivatives3b,11a,11b,12a, and12a, and12bare the products of a nucleophilic attack at the quinone methide system. The analysis of the13C‐NMR spectra led to the full assignment of the signals in1a,1b,2a,3a, and8a. Correlations by partial syntheses of3a, from coleon E(1a), after oxidation or acetylation/saponification of the latter, established the (R)‐configuration of the 2‐hydroxypropyl group in1a. The biomimetic transformation of plectrin (9) into (16R)‐coleon E (1a) is shown to proceedviathe unexpected, highly reactive 2‐methylspiro[cyclopropane‐1,2′‐(2′H)‐phenanthrene]‐1′,3′, 6′‐trione13. The solvolysis of the spiro(methylcyclopropane) moiety takes place with inversion of the configuration at the attacked C‐atom, as established in a previous communication. The 1,3,6‐trione13is supposed to be also the key intermediate in the biosynthesis of the allyl group in coleon F (2a) which proce

ISSN:0018-019X    

DOI:10.1002/hlca.19860690504

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractA general procedure for the design of synthetic vaccines with the retained conformational features of protein antigenic determinants is described. This new concept emerges from detailed studies on the relationship between primary sequence and secondary structure formation of synthetic peptides and takes advantage of the amphiphilic nature of epitope‐containing peptide segments in the native protein to accomplish structural modifications. These segments, for example amphiphilic helices or β‐sheets, are stabilized by the insertion of secondary structure‐inducing amino‐acid residues on the hydrophobic part of the peptide without affecting the spatial arrangement of functional residues on the hydrophilic side. The availability of amphiphilic peptides with tailor‐made conformational properties,e.g.helices, β‐sheets, and, moreover, assemblies of these blocks to structures of higher order (‘folding units’), allows the presentation and stabilization of continuous as well as discontinuous epitopes by this approach. This strategy is exemplified for the case of two discontinuous epitopes taken from lysozyme, which are matched to host molecules with adequate conformational features by the help of computer‐assisted molecular modelling. The implications of this new concept for the design of synthetic vaccines are discussed with special emphasis to the important role of peptide synthesis and chemical str

ISSN:0018-019X    

DOI:10.1002/hlca.19860690505

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractTreatment of the title compounds with either H3PO4or BF3· Et2O affords the bridged tricyclic lactones3and7as main products (57 and 70% yield, resp.). This is an efficient and novel access to specifically functionalised molecules possesing the bicyclo[3.2.1]octane skeleton. Lactones4and5and the bicyclic ketone6were formed as by‐products (2, 7, and 10% yield, resp

ISSN:0018-019X    

DOI:10.1002/hlca.19860690506

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractThe title compound1, {[Fe(H2pztc)(H2O)2] · 2 H2O}∞, has been prepared from pyrazinetetracarboxylic acid (H4pztc) and Fe(II) salt in H2O. It crystallizes in the monoclinic space groupP21/awith cell parametersa= 13.56(1) Å,b= 7.17(1) Å,c= 6.48(1) Å, β = 101.0(2)°,V= 618.4 Å3. The molecules form infinite parallel chains with bis(bidentate) coordination (through N and O) of the bridging pyrazine ligands. Twotrans‐COOH groups of the ligand remain uncoordinated, and twotrans‐H2O ligands complete a pseudo‐octahedral Fe(II) coordination which is distorted by the steric effect of the free COOH groups. The parallel polynuclear chains are linked through an extended network of H‐bonds involving the COO functions of the bridging ligand and the coordinated and lattice H2O molecules.Mössbauerand magnetic‐susceptibility data suggest normal paramagnetic behaviour of high‐spin Fe2+. An observed drop below 15 K in effective magnetic moment for1was attributed to temperature‐dependent population changes of the levels of the ground state5Γ, and not to antiferromagnetic coupling (J<1 cm−1). This result establishes that the obvious potential magnetic exchange pathway through the pyrazine bridges is inefficient, and this may be attributed, in part, to the high planar

ISSN:0018-019X    

DOI:10.1002/hlca.19860690507

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

The Absolute Configuration of the Spermine Alkaloid AphelandrineThe relative configuration of aphelandrine (1) was established by X‐ray structure determination. The absolute configuration of the centers 11 and 18 was determined earlier by chiroptic measurements. Therefore, structure1with the configurations 11S, 17S, and 18Srepresents the absolute configuration of aphelandrine. In the presence of base,1was converted to (11S, 17R, 18R) orantine (2). The1H‐NMR coupling constants between HC(17) and HC(18) (part of the dihydrofuran ring) are very much dependent on the substituent pattern of the amino N‐atoms N(6)

ISSN:0018-019X    

DOI:10.1002/hlca.19860690508

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

Quinazolinecarboxylic Acids. Synthesis of Alkyl [2‐(Ethoxycarbonyl)‐3,4‐dihydro‐4‐oxoquinazolin‐3‐yl]‐, [2‐(Ethoxycarbonyl)quinazolin‐4‐yloxy]‐ and (5,6,7,8‐Tetrahydro‐2‐phenylquinazolin‐4‐ylthio)alkanoatesThe [(2‐aminobenzoyl)amino]alkanoic acids and their esters1showed a different reaction behaviour with diethyl oxalate. Compound1(n = 2,3) was converted into the quinazolinylalkanoates3.o‐Aminohippurate yielded with ethyl (chloroformyl)formate a mixture of the amide4and the cyclized quinazolinone7b. Ethyl 3,4‐dihydro‐4‐oxoquinazoline‐2‐carboxylate (6) reacted with 2‐bromoalkanoates, in the presence of NaH, to the [2‐(ethoxycarbonyl)‐3,4‐dihydro‐4‐oxoquinazolin‐3‐y1]acetates7in the case of alkyl bromoacetate, and to theO‐alkylated derivatives8with the ethyl 2‐bromopropionate and ‐butyrate. 2‐Aminobenzamide (5) gave with ethyl 3‐(chloroformyl)‐2‐propenoate and methyl 3‐(chloroformyl)propionate the amides9or11, respectively, and not the expected quinazolinones. The cyclized product12was obtained from11and ethyl bromoacetate. Tetrahydroquinazolin‐4(3H)‐thione14was synthesized by the reaction of13with NH3, and it was alkylated at the S‐atom wi

ISSN:0018-019X    

DOI:10.1002/hlca.19860690509

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

2‐Aza‐1,3‐dienes. Synthesis and Properties of 1‐Alkylpyrazone‐imines and their TautomersTreatment of 5‐dialkylamino‐1,1‐dicyano‐2‐aza‐1,3‐dienes (or their 1‐methoxycarbonyl analogoues) with primary amines gives substituted 1‐alkyl‐3‐cyano‐(or methoxycarbonyl‐)pyrazoneimines. Tautomeric behaviour, nucleophilic addition to imino function and spectroscopic

ISSN:0018-019X    

DOI:10.1002/hlca.19860690510

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractTo investigate by NMR the effects of adenine methylation, a set of oligodeoxynucleotides has been synthesized by phosphotriester or phosphoramidite procedures on silica‐gel support. The preparation of fully protected 2′‐deoxy‐N6‐methyladenosine 3′‐phosphate4and (2′‐deoxy‐N6‐methyladenosin‐3′‐O‐yl)(methoxy)morpholinophosphine5is described. The large‐scale chemical synthesis, purification by HPLC, and characterization by MS of these molecules contain

ISSN:0018-019X    

DOI:10.1002/hlca.19860690511

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY