Identifizierung des acyclischen Zwischenproduktes der Nicotinsäure-Biosynthese, II. Synthese der Diastereomeren des ε-Hydroxy-β-carboxy-norleucins

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Abstract
The hitherto unknown amino acid [epsilon]-hydroxy-[beta]-carboxy-norleucine (IV) was synthesized and used in the identification of the acyclic precursor of nicotinic acid; its diastereomers were separated by chromatography. [delta]-Valerolactone was condensed with dimethyl oxalate; the product, a -methoxalyl-[delta]-valerolactone was converted into its dinitrophenylhydra-zone and into the corresponding isoxazolone (5-oxo-4-[3-hydroxy-propyl]-3-methoxycarbonylisoxazoline, IX). The dinitrophenylhydra-zone was hydrogenated to IV; the isoxazolone (IX) was characterized by its O-methyl- and N-methyl derivatives, and its structure confirmed by its UV, IR, NMR (nuclear magnetic resonance) and mass spectrum. The isoxazolone (IX) was converted into [epsilon] -hydroxy-norleucine by a catalytic decarboxylating hydrogenation. The decarboxylation, which is typical for isoxazol-5-ones, was avoided by using a reductive acyla-tion; [epsilon]-hydroxy-[beta]/3-carboxy-norleucine (IV) was then isolated on a preparative scale.

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