Synthesis of Four Stereoisomers of γ-Hydroxyarginine via the Corresponding Isomers of γ-Hydroxyornithine

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Abstract
Diastereomeric γ-hydroxy-l- and d-ornithines were prepared by reduction of the corresponding γ-oxoornithines synthesized from l- and d-histidines with sodium borohydride. The isomeric composition of the product obtained from l-histidine was estimated to be 68% erythro and 32% threo isomers and that of the product from d-histidine 65% erythro and 35% threo isomers by automatic amino acid analysis after conversion of the basic amino acids into neutral Nδ-acetyl derivatives. The diastereoisomers of each γ-hydroxyorni thine were separated by chromatography on a Dowex 50 column, four optically active isomers being isolated as their hydrochlorides in crystalline state. Guanidination of these isomers with 1-amidino-3,5-dimethylpyrazole nitrate (ADPN) gave the corresponding optically active isomers of γ-hydroxyarginine which were isolated as crystalline hydrochlorides. Erythro-γ-hydroxy-l-arginine hydrochloride shows a specific rotation which agrees very closely with that of natural product of γ-hydroxyarginine.