Die vier diastereomeren Ester 4ad aus D-( -)-N-Acetyl-a-phenylglycinol und den Titelverbindungen wurden chromatographisch an Kieselgel getrennt. Durch saure Hydrolyse wurden daraus die optisch aktiven N-Acetyl-Aminosauren 3ad kristallin gewonnen und charakterisiert. Die NMRund CD-Spektren von 3 und 4 erlauben die Bestimmung der relativen Konfigurationen, die durch Rontgenstrukturanalyse abgesichert wurden. Chemische Korrelationen mit den 2-Cyclopentylglycinen bekannter Konfiguration lieferten die absoluten Konfigurationen von 3ad. Nur(2S, 1'R)-( +)-3b ist biologisch aktiv.
On Amino Acid Antagonists, V*). -Separation and Determination of the Configurations of the Stereoisomeric N-Acetyl-2-(2'-cyclopentenyl)glycinesThe mixture of the four diastereorneric esters 4ad of the title compounds and D( -)-N-acetyla-phenylglycinol were separated chromatographically on silica gel. Acid hydrolysis of the esters yielded the optically active acids 3a-d which are crystalline and fully characterized. Interpretation of the NMR and CD spectra of 3 and 4 leads to the relative configurations. These were corroborated by X-ray analysis. The absolute configurations of 3a-d were determined by chemical correlation with the N-acetyl-2-cyclopentylglycines of known configurations. Only 3b with (2S,l'R)-configuration shows biological activity.In der voranstehenden Publikation') haben wir die Trennung und Bestimmung der absoluten Konfiguration der diastereomeren N-Acetyl-2-(2'-cyclohexenyl)glycine 1 beschrieben. Die gleiche Strategie wurde fur die Trennung und Bestimmung der Konfigurationen der N-Acetyl-2-(2'-cyclopentenyl)glycine 3 verfolgt. Beide Verbindungen, 1 und 3, hemmen das Wachstum von E. coli auf Minimalmedium3p4).Die freie Aminosaure 2 ist leicht nach Dennis et al.4' zuganglich (Schema 1). N-Acetylierung liefert 3, welches sich wie 2 nicht durch fraktionierende Kristallisation in die Diastereomeren auftrennen lafit. Die Diastereomeren-Anteile konnen jedoch aus den 'H-NMR-und 13C-NMR-Spektren bestimmt werden ( Abb. 1 und 2).
Abstract The preparative column chromatographic separation on small grained silica gel of the bacteriophaeophorbide-c- and -d-methyl esters into their homologous and isomeric components is described. The influence of particular regions of the molecule, which carry different alkyl-substituents, on the chromatographic separability is selectively enhanced through the variation of the eluent. Mass and 1H NMR spectra of the pure components are discussed.
GLC analysis of the crude reaction products revealed yields of over 90 % of the corresponding esters. The yields of isolated esters were lower (62-85 %), this being partly due to difficulties in the separation of the esters ( 5 ) from the excess alcohol employed (Table 1).Received: August 28, 1978 [Z 94 IE] German version: Angew. Chem. 90, 995 (1978) nucleus. The spatial position of the N-C--H atom is [ l ] 1. Prim, J . W Verhoeven, 7: J . de Boer, Org. Magn. Reson. 9, 543 (1977), and references cited therein. Angew. Chem. I n t . Ed. Engl. 17 (1978) N o . 12
were dissolved in benzene and the solution subjected to chromatographic separation on a silica-gel-60 column with benzene.Weight for weight, the ellipticities of the two enantiomer fractions were of the same magnitude but of different sign ( f 2 %).This is indicative of complete separation, for otherwise equal values with opposite signs can occur only when the precipitated enantiomers and those remaining in solution each contain the same proportion of the other enantiomerr']. The optical activity was not increased by a second resolution step.In contrast to the analogous carbon compounds ( 3 ) is not cyclized to ( 4 ) in toluene/iodine with polarized lightr*]. This is consistent with the photochemical behavior of azobenzene. A protonated form, which in the case of azobenzene can be photocy~lized[~~, is not formed-even in 70% perchloric acid.
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