Esters of N-protected amino acids with o-hydroxybenzaldehyde oxime, o-hydroxyacetophenone oxime, o-hydroxybenzophenone oxime, and their 5-Cl and 5-NO2 derivatives were prepared by several methods. Various dipeptide derivatives with high purity were obtained in good yield by use of these active ester reagents.

Aus entsprechenden geschützten Aminosäuren (I) und Oximen (III) werden Aktivester des Typs (II) synthetisiert, von denen die meisten der im Formelschema angegebenen tabelliert sind [die Ausb. sind stark unterschiedlich (39‐86%)].

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Active esters (1) of glycine with o-hydroxybenzaldehyde oxime, o-hydroxyacetophenone oxime, o-hydroxybenzophenone oxime, and their 5-Cl and 5-NO2 derivatives were prepared by several methods. For aminolysis with benzylamine, esters 1 show higher reactivity than similar esters containing no hydroxyl group in the ortho position. It is suggested that esters 1 forms an intramolecular hydrogen bond between the hydrogen of the hydroxyl group at the ortho position and the hydroxyimino nitrogen so as to have its carbonyl group activated for the aminolysis; this mechanism of activation seems to be a sort of “intramolecular acid-catalysis.” Among the series of esters 1, esters of o-hydroxybenzaldehyde oxime and its 5-Cl and 5-NO2 derivatives are most reactive in the aminolysis. The reactivity of esters 1 is also discussed in relation to pKa values of aromatic o-hydroxy oximes.

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