Helvetica Chimica Acta

doi: 10.1002/hlca.19860690701pmid: N/A

Baumberger, Franz; Vasella, Andrea

doi: 10.1002/hlca.19860690702pmid: N/A

The synthesis of 5‐acetamido‐4‐deoxyneuraminic acid (1) is described. Acetylation of a mixture of the epimeric triols 4 and 5 gave the tetraacetates 7 and 8 (Scheme 1). Ozonolysis of a mixture of these acetates followed by base‐promoted β‐elimination led to the (E) ‐configurated α,β‐unsaturated keto ester 10, which was hydrogenated to give the saturated keto ester 11. Saponification of 11 and hydrolytic removal of the benzylidene group followed by anion‐exchange chromatography gave the 5‐acetamido‐4‐deoxyneuraminic acid (1, Scheme 1 and 2). De‐O‐acetylation (NaOMe/MeOH) of the keto ester 11 gave a mixture of the tert‐butyl ester 12 and the methyl ester 13, which were converted to tert‐butyl N‐acetyl‐4‐deoxyneuraminate (14) and to methyl N‐acetyl‐4‐deoxyneuraminate (15), respectively. Hydrogenolysis of the benzylidene acetal 11 followed by de‐O‐acetylation gave the pentahydroxy ester 16.

Oppolzer, Wolfgang; Mills, Robert J.; Pachinger, Werner; Stevenson, Thomas

doi: 10.1002/hlca.19860690703pmid: N/A

EtAlCl2‐promoted additions of organocopper reagents to camphor‐derived, conjugated N‐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 (via silyl‐directed α‐methylation).

Müller, Paul; Rodriguez, Domingo

doi: 10.1002/hlca.19860690704pmid: N/A

A 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‐1 H‐cyclobuta[a]cyclopropa[d]benzene (4e) have been synthesized and characterized. Dissolution of these difluoro derivatives in fluorosulfonic acid affords the fluoro cations 3a–e. 1H‐, 19F‐, and 13C‐NMR data of the cations are reported and discussed with respect to those of the precursors.

de Almeida, Ligia Bicudo; De Vuono Camargo Penteado, Marilene; Simpson, Kenneth L.; Britton, George; Acemoglu, Murat; Eugster, Conrad Hans

doi: 10.1002/hlca.19860690705pmid: N/A

Luteochrome isolated from the tubers of a white‐fleshed variety of sweet potato (Ipomoea batatas LAM.) 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 (1 and 2, 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 from the α‐side, irrespective of the presence of OH groups on the ring.

Duthaler, Rudolf O.; Ginsburg, David

doi: 10.1002/hlca.19860690706pmid: N/A

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

Holze, Gerhard; Gossauer, Albert; Ernst, Ludger

doi: 10.1002/hlca.19860690707pmid: N/A

Structure and Reactivity of Xanthocorrinoids. C(15) Hydroxylation of the Corrin Chromophore on Reaction of Cyanocob(III)alamin with Udenfriend's Reagent

Kräutler, Bernhard; Hughes, Mark; Caderas, Christian

doi: 10.1002/hlca.19860690708pmid: N/A

Separate 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 to 2 + 3 ⇄ 4 + 5. The corresponding equilibrium constant Ke was 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 such as 5.

Lang, Marc; Hungerbühler, Ernst; Schneider, Peter; Scartazzini, Riccardo; Tosch, Werner; Konopka, Edward A.; Zak, Oto

doi: 10.1002/hlca.19860690709pmid: N/A

In continuation of our work on penem antibiotics, novel chiral (5R,6S)‐2‐(1′‐aminoalkyl)‐6‐(hydroxyalkyl)‐derivatives 1 have been synthesized by two essentially different strategies. Whereas the starting materials for 1a‐f, azetidinones 2 and 5, were obtained from chiral building blocks (6‐aminopenicillanic acid and L‐threonine, resp.), the one for 1g, azetidinone 9, was derived from racemic 4‐acetoxyazetidinone and, as chiral auxiliary, (2R)‐2‐mercaptopropan‐1‐ol. The 2‐aminomethyl derivatives 1a (CGP 30 779) and 1f (CGP 31 608) proved the most potent compounds in the antibacterial tests in vitro and showed a well‐balanced spectrum of activity by comparison with that of established β‐lactams.

D'Ambrosio, Michele; Guerriero, Antonio; Fabbri, Daniele; Pietra, Francesco

doi: 10.1002/hlca.19860690710pmid: N/A

The Mediterranean stolonifer Sarcodictyon 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‐en‐1‐one; (+)‐1a).