摘要:

Abstract(1S,2R,6R,7R)‐4‐Phenyl‐3,10‐dioxa‐5‐azatricyclo[5.2.1.02,6]dec‐4‐en‐9‐one ((+)‐5) obtained in 6 steps from theDiels‐Alderadduct of furan to 1‐cyanovinyl (1S)‐camphanate ((+)‐3) was reduced to the correspondingendo‐alcohol (−)‐6the treatment of which with HBr/AcOH provided (−)‐(3aS,4S,6R,7S,7aR)‐4β‐bromo‐3aβ,4,5,6,7,7aβ‐hexahydro‐2‐phenyl‐1,3‐benzoxazole‐6β,7α‐diyl diacetate ((−)‐17). Elimination of HBr with 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) and acidic hydrolysis furnished (−)

ISSN:0018-019X    

DOI:10.1002/hlca.19940770103

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Abstract2′–5′ Adenylate trimers41–44carrying the (tert‐butyl)dimethylsilyl (tbds) group at the 3′‐OH position of various sugar moieties were synthesizedviathe phosphoramidite method. The use of the (tert‐butyloxy)carbonyl (boc) and 2‐(4‐nitrophenyl)ethylsulfonyl (npes) groups for 2′‐OH protection in neighbourhood to the 3′‐O‐tbds residue was compared during the synthesis of the target trimers. For other functional positions, the use of the 2‐(4‐nitrophenyl)ethyl (npe) and 2‐(4‐nitrophenyl)ethoxycarbonyl

ISSN:0018-019X    

DOI:10.1002/hlca.19940770104

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractA new and generally applicable synthetic path for the preparation of heteroditopic bis‐macrocycles using tri‐N‐protected tetraazacycloalkanes as building blocks and bromoacetyl bromide as bridging reagent is described. In the first step, bromoacetyl bromide is used as acylating agent for one of the macrocycles, whereas in the second step it is used as alkylating agent for the second macrocycle, thus giving protected bis‐macrocyclic amides (e.g.6). After reduction of the amide moiety and deprotection, bis‐azamacrocycles with an ethylene bridge are obtained (e.g.8). The corresponding homoditopic bis‐macrocycles16and17are also prepared for comparison purpose. Spectrophotometric studies indicate that bis‐macrocycle8, which consists of a 12‐ and a 14‐membered ring, binds two metal ions with equal affinity, whereas compound13, in which an unsubstituted (cyclam) and a trimethyl‐substituted tetraazacyclotetradecane unit (Me3cyclam) are bridged, shows selective metal‐ion binding. The first metal ion is always incorporated into the cyclam unit, whereas the second one binds to the Me3cyclam macrocycle. Thus, by sequential addition of two different metal ions, heterobinuclear complexes can easily be prepared. The electrochemistry of the binuclear Ni2+complexes, studied by CV and DPV, as well as the EPR spectra of the binuclear Cu2+complexes clearly indicate met

ISSN:0018-019X    

DOI:10.1002/hlca.19940770105

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractFlash‐vacuum thermolysis of the four diastereoisomeric 5,6‐epoxy‐5,6‐dihydro‐caryophyllenes1–4at 500–550°/0.1–0.7 Torr leads to the hitherto unreported enantiomers of (6RS,7RS)‐ and (6RS,7SR)‐6,7‐epoxy‐6,7‐dihydro‐β‐farnesenes ((±)‐5and (±)‐6, resp.). In particular, (+)‐5is formed in 45% yield (ca.90% ee) and is, thus, an attractive chiral build

ISSN:0018-019X    

DOI:10.1002/hlca.19940770106

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractThe one‐electron transfer to large π‐delocalized hydrocarbons provides an interesting possibility to crystallize solvent‐separated ion‐pair salts containing optimally solvated cations. Accordingly, the reduction of 9,10‐diphenylanthracene in aprotic THF solution at a sodium metal mirror allows to grow dark‐blue prismatic crystals of its radical anion and sixfold THF‐solvated sodium cation. The structure of the radical anion is very similar to that recently published for the neutral molecule. According to AM1 hypersurface calculations based on the structural data, the phenyl twist angles obviously must be determined by lattice packing, and the negative charge is delocalized predominantly within the anthracene π system. The counter cation [Na⊕(THF)6], reported ordered for the first time, shows nearly octahedral coordination within a rather densily packed solvent shell. Due to the strong repulsions between the solvent molecules, its isodesmically calculated solvation enthalpy is smaller than that of the analogous dimethoxyethane co

ISSN:0018-019X    

DOI:10.1002/hlca.19940770107

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractA series of ceramides, called oceanapins A–F (2–7), which are unique for branching at both the sphingosine and fatty‐acid chains, have been isolated as pure compounds from the haplosclerid spongeOceanapiacf.tenuisof the Coral Sea. Following acid hydrolysis, both the fatty‐acid and the sphingosine portions were obtained separately, which allowed their unequivocal structural definition. The absolute configuration was securedviaprotection of C(1′)–OH andMosher'sesterification at C(3′)–OH of

ISSN:0018-019X    

DOI:10.1002/hlca.19940770108

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Abstractβ‐Nitrostyrene derivatives of adenosine 5′‐glutarates are potent and selective bisubstrate‐type inhibitors of the epidermal growth factor receptor protein tyrosine kinase (EGF‐R PTK). In an attempt to improve the inhibitory activity, this type of compounds was modified with alkyl spacers of varying length between the nitrostyrene and the glutaryl units. The spacers consisted of 1, 3, 4, and 5 atoms to give compounds of the benzyl, oxyethyl, oxypropyl, and oxybutyl series, respectively (Schemes 1and2). Adenosine 5′‐esters were prepared in the benzyl and oxypropyl series only. Compared to the compounds in the parent series without spacer (IC50= 0.7–12 μM), most of the modified compounds inhibited the EGF‐R PTK only marginally or were inactive (IC50≥ 100 μM). The only exceptions were the free acids19and20withIC50values ofca.5 μM. It is noteworthy that esterification of these two hydrogen glutarates with either MeOH or adenosine yielded inactive compounds, which is in contrast to the corresponding sub

ISSN:0018-019X    

DOI:10.1002/hlca.19940770109

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractThe biphenyl‐containing pseudo‐amino acids 2′‐(aminomethyl)biphenyl‐2‐carboxylic acid (Abc;1) and 2′‐(aminomethyl)biphenyl‐2‐acetic acid (Aba;2) are used as rigid spacers in the backbone of the cyclic peptides cyclo (‐Abc‐Ala‐Phe‐Gly‐)2(5), cyclo(‐Abc‐Ala‐Val‐Gly‐)2(6), cyclo(‐Aba‐Gly‐Phe‐Ala‐)2(7), and cyclo(‐Aba‐Ala‐Phe‐Gly‐)2(8). Three different interconverting diastereoisomers are found in solutions of each of these cyclopeptides due to the atropisomerism of the biphenyl units. NMR Techniques and molecular‐dynamics calculations allow to conclude that the major diastereoisomer of5(and6) in (D6)DMSO adopts a β‐sheet conformation. It is proposed that the pseudo‐amino acid1of (R)‐chirality forms, with attachedL‐amin

ISSN:0018-019X    

DOI:10.1002/hlca.19940770110

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Abstract14N‐ and1H‐Coupling constants, determined by ESR, ENDOR, and general‐TRIPLE‐resonance spectroscopy, are reported for the radical cations of tetrazinodi(heteroarenes)1–8. The results comply with the expectation that donor properties of these compounds are mainly due to the electron‐rich dihydrotet

ISSN:0018-019X    

DOI:10.1002/hlca.19940770111

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Vitamin‐B12‐Catalyzed C, C‐Bond Formation: Synthesis of JasmonatesviaSequential Radical ReactionThe Cbl‐catalyzed electroreduction of 3‐(2′‐bromo‐1′‐ethoxyethoxy)cyclopenten (1a) in presence of 1‐cyanovinyl‐acetate (8) gave, in a sequential radical reaction (5‐exo‐trig‐cyclization of1afollowed by addition to8), 1‐cyano‐2‐(2′‐ethoxy‐hexahydro‐2′H‐cyclopenta[b] furan‐4′‐yl)ethyl acetate (10a). This intermediate was transformed to methyl jasmonate (7; four steps) and epituberolide (9; three steps) in 20

ISSN:0018-019X    

DOI:10.1002/hlca.19940770112

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY