摘要:

AbstractControlled ozonolysis of 2,3,5,6‐tetramethylidene‐7‐oxabicyclo[2.2.1]heptane (1) afforded 3,5,6‐trimethylidene‐7‐oxabicyclo[2.2.1]heptan‐2‐one (2). Ozonolysis of 2 gave a 1:1 mixture of 3,5‐dimethylidene‐7‐oxa‐bicyclo[2.2.1]heptane‐2,6‐dione (3) and 3,6‐dimethylidene‐7‐oxabicyclo[2.2.1]heptane‐2,5‐dione (4). The He(Iα) photoelectron (PE) spectra of2and4have been recorded. Comparison with the PE data of related systems, and with the result ofab initioSTO‐3G calculations, confirm the existence of significant through‐bond interactions between the oxygen lone‐pair orbitals n(CO) of the carbonyl

ISSN:0018-019X    

DOI:10.1002/hlca.19900730102

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe (12–20)‐nonapeptide Z‐Leu‐Aib‐Pro‐Val‐Aib‐Aib‐Glu (OBzl)‐Gln‐Pheol (10) of the ionophor alamethicin was synthesized by a new strategy, using 3‐amino‐2,2‐dimethyl‐2H‐azirines 2 as synthons for the α‐a

ISSN:0018-019X    

DOI:10.1002/hlca.19900730103

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractSeveral homo‐ and heteronuclear two‐dimensional NMR techniques were used to assign all H‐ and C‐resonances of the two conformers A and B of [7‐(N‐methyl‐L‐leucine)]didemnin B. Didemnine is a biologically highly active cytostaticum and immunosuppressivum. The assignment of the aliphatic C‐atoms were done by the inverse H,C‐COSY with TOCSY transfer which connects complete proton spin systems and represents them on C‐atoms. The structure of both conformers (AandB) in (D6)DMSO solution was derived from homo‐ and heteronuclear couplings (J), temperature dependencies of NH protons, and NOE effects. Distances determined from the latter were used for refinements by restrained MD calculations using the GROMOS program. The solution structure of [Me‐L‐Leu7]didemninB(AandB) was compared to that of didemnin B. The backbone structure of the macrocyclic ring and of the linear side‐chain moiety are very similar in conformerAand didemninB, though the Ist1‐Hip2region of the ring is slightly ex tended in conformerA. This may be caused by the influence of the Me‐L‐Leu7residue in A and may be responsible for its reduced biological activity in comparison to didemninB. The more weakly populated conformerBexhibits a βVI

ISSN:0018-019X    

DOI:10.1002/hlca.19900730104

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

Synthesis of Plectranthons, Diterpenoid Phenanthrene‐1,4‐dionesThe following phenanthrene‐1,4‐diones have been synthesized by using the photocyclization of the corresponding highly substituted stilbenes as the key step: 3‐hydroxy‐5,7,8‐trimethyl‐2‐(prop‐2‐enyl)phenanthrene‐1,4‐dione (1), (RS)‐, (R)‐, and (S)‐2‐[3‐hydroxy‐5,7,8‐trimethyl‐1,4‐dioxophenanthren‐2‐yl]‐1‐methylethyl acetate (2,31, and32, resp.), 3‐hydroxy‐7,8‐dimethyl‐2‐(prop‐2‐enyl)phenanthrene‐1,4‐dione (3), 3‐hydroxy‐7,8,10‐tri‐methyl‐2‐(prop‐2‐enyl)phenanthrene‐1,4‐dione (4), 5,7,8‐trimethyl‐2‐(prop‐2‐enyl)phenanthrene‐1,4‐dione (17), and 3‐hydroxy‐2‐methylphenanthrene‐1,4‐dione (42). The quinones1and3proved to be identical with the recently isolated plectranthonsAandC.Compounds2,31, and32exhibited the same UV/VIS, IR,1H‐NMR and mass spectra as natural plectranthonB, but had different melting points. This might be due either to crystal modifications or to diastereoisomerism caused by the helical structure of the phenanthrene‐1,4‐dione skeleton. The spectral data of synthetic4were not compatible with those of natural plectranthon D for which structure 4 had been proposed based mainly on1H‐NMR arguments concerning the chemical shifts of HC(9) and HC(10) in 1–3. Extensive1H‐NMR investigations have now revealed that the currently stated assignments of the HC(9)/ HC(10)ABsystem have to be reversed for highly substituted phenanthrene‐1,4‐diones: in the model compounds 2‐methylphenanthrene‐1,4‐dione (41) and 2, HC(10) resonates al lower field as expected (peri‐position), whereas in the highly substituted con

ISSN:0018-019X    

DOI:10.1002/hlca.19900730105

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractAccording to a general concept for the total synthesis of pseurotin A (1), a secondary metabolite ofPseudeurotium ovalisSTOLK, 5‐[(1S,2S,Z)‐1,2‐dihydroxyhex‐3‐enyl]‐2,2,4‐trimethylfuran‐3(2H)‐one (17) was prepared. It is a model substance for the substituted furan‐3(2H)‐one moiety of1. The aldol condensation of the aldehyde26, derived from D‐glucose, and the enolate of ketone2

ISSN:0018-019X    

DOI:10.1002/hlca.19900730106

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe isothiazole1is not only a dipolarophile but also a reactive and versatile dienophile: especially with oxy‐substituted ‘donor’ 1,3‐butadienes, it readily combines inDiels‐Alderfashion; the regiospecificity of the addition is governed by the carbonyl group of the dienophile, whereas the sulfo group can be ignored for the purpose of predicting regioselectivity. upon dehydrobromination of the [4 + 2] adducts with DBN, the cycloaromatization process is completed, generating saccharin‐like compounds. Besides the parent substance saccharin (14b), several hydroxylated derivatives have been synthesized by this new method; two of them,i.e.16band18c, are of potential interest as non‐nutritive sweetening agents (Scheme 3). In an alternative version of this principle, the isothiazole22is reacted with the renowned oxazole21, affording, after acid‐promoted rearrangement, pyrido‐annelated isothiazoles25(Scheme 4). Since both processes generate saccharin‐related structures, they may serve in syntheses of oxicams and analogs of ipsapirone. To demonstrate the viability of the approach, one representative of each series,i.e.26aand29, has been converted to an oxicam (7band3

ISSN:0018-019X    

DOI:10.1002/hlca.19900730107

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

Charge‐Transfer Complexes of Tetrazinodiheteroarenes with Acceptor CompoundsThe formation of charge‐transfer complexes and radical‐ion pairs of donor compounds1–6with acceptor compounds7–12has been investigated by means of VIS/NIR‐spectroscopic methods. The equilibrium constantsKCTup to 1100M‐1 for the donor/acceptor couple dipyrido[1,2‐b:1,2′‐e][1,2,4,5]tetrazine (2)/ethylenetetracarbonitrile (11) and spectra of the CT complexes have been determined in 1,2‐dichloroethane solution at 25°. Results are discussed in relation to known CT‐complex properties and to voltammet

ISSN:0018-019X    

DOI:10.1002/hlca.19900730108

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractNα[(tert‐Butoxy)carbonyl]‐2‐diazo‐L‐histidine methyl ester1was synthesized starting from the corresponding L‐histidine derivative. The physico‐chemical properties of this new photoactivatable amino‐acid derivative were established. The synthetic precursor of1, 2‐amino‐L‐histidine derivative3, was best isolated and characterized as 2‐amino‐Nα‐[(tert‐butoxy)carbonyl]‐Nτ‐tosyl‐L‐histidine methyl ester (4). Selective deprotections of4(Nα‐Boc,Nα‐Tos, COOMe) were achieved, thus allowing the use of the corresponding products in peptide synthesis. The optically active dipeptides8and9were synthesized by coupling 2‐amino‐Nτ‐tosyl‐L‐histidine methyl ester (5) withN‐[(tert‐butoxy)carbonyl]‐L‐alanine andNα‐[(tert‐butoxy)carbonyl]‐Nτ‐tosyl‐L‐histidine (6) with L‐alanine methyl ester, respectively. The question of selective diazotization of a 2‐aminohistidine residue in a synthetic peptide was studied using competitive diazotizations between 2‐amino‐1H‐imidazole and several amino‐acid derivatives susceptible to undergo nitrosylation. The results show that synthetic photoactivatable

ISSN:0018-019X    

DOI:10.1002/hlca.19900730109

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

Abstract1,3,5‐Trideoxy‐1,3,5‐tris(dimethylamino)‐cis‐inositol (TDCI) and 1,3,5‐trideoxy‐1,3,5‐tris(trimethylammonio)‐cis‐inositol (TTCI) were prepared by methylation of 1,3,5‐triamino‐1,3,5‐trideoxy‐cis‐inositol (TACI). The ability of TDCI to form both intermolecular and intramolecular H‐bonds, as demonstrated by X‐ray diffraction, is probably responsible for the good solubility of TDCI in almost every common solvent. TTCI was found to be a polyol of unusual high acidity (pK1= 8.14 ± 0.02, pK2= 13.0 ± 0.2). This phenomenon could be explained by electrostatic interactions between the charged subs

ISSN:0018-019X    

DOI:10.1002/hlca.19900730110

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe lithium and europium(III) cryptates of a macrobicyclic ligand1incorporating the 3,3′‐biisoquinoline 2,2′‐dioxide2have been prepared. The Eu(III) complex [Eu(2)2]Cl3has also been obtained. These Eu(III) complexes present characteristic1H‐NMR spectra containing markedly shifted resonances. They are strongly luminescent; the emission spectra, quantum yields, and lifetimes have been d

ISSN:0018-019X    

DOI:10.1002/hlca.19900730111

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY