Oxidation of Amino Acid Derivatives and Piperazinediones

Direct Oxidation of Amino Acid Derivatives and Piperazinediones 

Little is known about the direct oxidation of amino acid derivatives. Although an a-acetoxy derivative can be prepared from hippuric acid by treatment with lead tetraacetate (99) this reaction is not applicable to N-phthaloyl- or N-benzyloxycarbonyl-glycine. Anodic oxidation of acetamidomalonic acid monoester in alcohol yielded the ot-alkoxy-a-acetamino acetic acid, while in acetic acid the corresponding oc-acetoxy compound was obtained (186). The oxidation of optically active N-salicylidene-alanine cobalt (III) complexes has been studied as a model reaction for enzymatic deamination of a-amino acids, and found to yield the corresponding diastereomeric a-hydroxy alanine complexes (118). 

With regard to the biosynthesis of the epidithiopiperazinediones, U. Schmidt and J. Hausler studied the photochemical oxidation of piperazinediones in some detail (168, 349), a reaction which takes place with exceptional ease in many cases. Piperazinediones which are not kept sealed in an oxygen-free atmosphere contain, if exposed to light, considerable amounts of hydroperoxides within a few weeks. Photochemical oxidation of piperazinediones in the presence of catalytic quantities of benzophenone yields mono- and bis-hydroperoxides in which the configuration of the original compounds is largely retained. As an example, the main product of photochemical oxidation of L-prolyl-L-proline 

Interconversion of a-Hydroxy- and a-Mercapto-a-amino Acids, Hydroxy- and Mercaptopiperazinediones, Pyruvoylamino Acid Amides and Dehydropeptides 

Feasible biological relationships between a-keto-co-acylamino acid amides and the epidithiopiperazinediones were demonstrated by E. Ohler and U. Schmidt (255). In weakly acid aqueous solution the acetal (69) underwent hydrolysis followed by double ring closure to the dihydroxy-piperazinedione (70). The latter could be converted by treatment with hydrogen sulfide into the cis-dimercaptan, which yielded the epidisulfide 

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B. Direct Oxidation of Amino Acid Derivatives and Piperazinediones.285... 

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