摘要:

AbstractThe synthesis of 5‐acetamido‐4‐deoxyneuraminic acid (1) is described. Acetylation of a mixture of the epimeric triols4and5gave the tetraacetates7and8(Scheme 1). Ozonolysis of a mixture of these acetates followed by base‐promoted β‐elimination led to the (E) ‐configurated α,β‐unsaturated keto ester10, which was hydrogenated to give the saturated keto ester11. Saponification of11and hydrolytic removal of the benzylidene group followed by anion‐exchange chromatography gave the 5‐acetamido‐4‐deoxyneuraminic acid (1,Scheme 1and2). De‐O‐acetylation (NaOMe/MeOH) of the keto ester11gave a mixture of thetert‐butyl ester12and the methyl ester13, which were converted totert‐butylN‐acetyl‐4‐deoxyneuraminate (14) and to methylN‐acetyl‐4‐deoxyneuraminate (15), respectively. Hydrogenolysis of the benzylidene acetal11followed by de

ISSN:0018-019X    

DOI:10.1002/hlca.19860690702

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractEtAlCl2‐promoted additions of organocopper reagents to camphor‐derived, conjugatedN‐enoyl‐sultams gave saturated and olefinic β‐silylcarboxyl derivatives with high diastereodifferentiation. Nondestructive removal of the chiral auxiliary followed by oxidative Si‐C bond cleavage furnished enantiomerically pure acetate‐derived aldols and propionate‐derived ‘anti’ ‐aldols (viasilyl

ISSN:0018-019X    

DOI:10.1002/hlca.19860690703

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractA series of 3,4‐disubstituted (4a,b) or 3,4‐fused (4c‐e) 1,1‐di‐fluorocyclopropabenzenes, including the very strained 1,1‐difluoro‐3,4‐dihydro‐1H‐cyclobuta[a]cyclopropa[d]benzene (4e) have been synthesized and characterized. Dissolution of these difluoro derivatives in fluorosulfonic acid affords the fluoro cations3a–e.1H‐,19F‐, and13C‐NMR data of the cations are reported and discussed with respect

ISSN:0018-019X    

DOI:10.1002/hlca.19860690704

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractLuteochrome isolated from the tubers of a white‐fleshed variety of sweet potato (Ipomoea batatasLAM.) has been shown by HPLC,1H‐NMR and CD spectra to consist of a mixture of (5R,6S,5′R,8′R)‐ and (5R,6S,5′R,8′S)‐ 5,6:5′,8′‐diepoxy‐5,6,5′,8′‐tetrahydro‐β,β‐carotene (1and2, resp.). Therefore, its precursor is (5R,6S,5′R,6′S)‐5,6:5′,6′‐diepoxy‐5,6,5′,6′‐tetrahydro‐β,β‐carotene (4). This is the first identification of luteochrome as a naturally occurring carotenoid and, at the same time, gives the first clue to the as yet unknown chirality of the widespread β,β‐carotene diepoxide. These facts demonstrate that the enzymic epoxidation of the β‐end group occurs fr

ISSN:0018-019X    

DOI:10.1002/hlca.19860690705

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractThe relative configuration of the title compounds has been determined by1H‐NMR measurements at 300 MHz. In contradistinction to prevailing opinion, it was found that 4‐oxo derivatives prefer thecis‐configuration. While thecis/transratio is 82:18 for the parent 1,2,3,4,4a,9,10,10a‐octahydrophenanthrene‐4,9‐dione, thetrans‐isomers of C(5)‐substituted derivatives cannot be detected under the conditions of equilibration. Thecis‐configuration is retained upon acetalization of the 4‐oxo derivative. A warning is issued regarding the assigned configurations of certain intermediates in theElad‐Ginsburg

ISSN:0018-019X    

DOI:10.1002/hlca.19860690706

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

Structure and Reactivity of Xanthocorrinoids. C(15) Hydroxylation of the Corrin Chromophore on Reaction of Cyanocob(III)alamin withUdenfriend's ReagentHydroxy‐corrinoid4represents a new type of corrin derivatives whose chromophore is identical with that of products formed on bacterial degradation of cyanocob(III)alamin (1).In vitro,4is obtained by O2oxidation of1in the presence of ascorbic acid and cupric ion

ISSN:0018-019X    

DOI:10.1002/hlca.19860690707

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractSeparate neutral aqueous solutions of either (a) methylcob(III)alamin (2) and (heptamethyl cob(II)yrinate) perchlorate (3) or of b) cob(II)alamin ( = vitamin B12r; (4) and [Coβ‐methyl(heptamethyl cob(III)yrinate)] perchlorate (5) equilibrated thermally at r.t. according to2 + 3 ⇄ 4 + 5. The corresponding equilibrium constantKewas determined (Ke= 0.63 ± 0.15). This equilibration experiment indicates that the coordination of the nucleotide function in methylcob(II)alamin (2) hardly affects the thermodynamics of the CoC bond homolysis in aqeous solution when compared to nucleotide‐free methylcorrinoids

ISSN:0018-019X    

DOI:10.1002/hlca.19860690708

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractIn continuation of our work on penem antibiotics, novel chiral (5R,6S)‐2‐(1′‐aminoalkyl)‐6‐(hydroxyalkyl)‐derivatives1have been synthesized by two essentially different strategies. Whereas the starting materials for1a‐f, azetidinones2and5, were obtained from chiral building blocks (6‐aminopenicillanic acid and L‐threonine, resp.), the one for1g, azetidinone9, was derived from racemic 4‐acetoxyazetidinone and, as chiral auxiliary, (2R)‐2‐mercaptopropan‐1‐ol. The 2‐aminomethyl derivatives1a(CGP 30 779) and1f(CGP 31 608) proved the most potent compounds in the antibacterial testsin vitroand showed a well‐balanced spectrum of activity by comparison w

ISSN:0018-019X    

DOI:10.1002/hlca.19860690709

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractThe Mediterranean stoloniferSarcodictyon roseum( =Rolandia rosea) (Cnidaria, Anthozoa, Alcyonaria, Stolonifera, Clavulariidae) contains the first example of a chiral, optically active prenyl derivative of a reduced benzoquinone, sarcodictyenone (= (+)‐(4R*,5R*)‐5‐geranylgeranyl‐4‐hydroxy‐2‐methylcyclohex‐2‐

ISSN:0018-019X    

DOI:10.1002/hlca.19860690710

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractAllenic acids are found to add to dicyclohexylcarbodiimide affording, in the presence of secondary amines, the 1,3‐oxazine‐4‐ones.5. Under neutral conditions, they add to diaryl‐ or aryl(cyclohexyl)carbodiimides and triphenylketen‐imine to give the corresponding tricyclo[5.2.2.01,5]undecatriene‐3

ISSN:0018-019X    

DOI:10.1002/hlca.19860690711

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY