Synthesis of Octopine (Pectenine)

Abstract

The compound isolated by Moore and Wilson 1 from Pecten muscle and called pectenine by them is probably identical with octopine previously isolated by Morizawa. 2 The arguments in favor of this statement will be given in a forthcoming publication.

Octopine was characterized by Moore and Wilson and, on evidence which was not quite complete, they concluded that the compound is probably arginine, the α-amino group of which is attached to the α-carbon atom of propionic acid. In order to confirm this conclusion a synthesis has been carried out as follows 3 : d-arginine methyl ester dihydrochloride was treated with the ethyl ester of d-1, α-bromopropionic acid in absolute ethyl alcohol containing a little zinc dust and potassium iodide. Two equivalents of sodium ethylate were added at once and another equivalent added during the early part of the period of boiling which was continued for 24 hours. The esters were hydrolyzed with acid and the material was precipitated by silver and baryta. After decomposing the precipitate, the small amount of arginine was removed with flavianic acid and a picrate was obtained from the filtrate after extraction of the flavianic acid.

The recrystallized picrate melted with decomposition at 219°. Octopine picrate melted at 224° and a mixed melting point was 219° (all uncorr.). The new picrate when analyzed by the Jorpes modification of the Sakaguchi method gave 97% of the expected color when octopine was used as a standard. The color given by the new picrate with the Sakaguchi reagents was identical with the purple color given by octopine. Picric acid analysis yielded the following results : Calculated for C₉H₁₈N₄O₄.C₆H₃N₃O₇ 48.20'%, found 48.31%. The compound showed no free amino nitrogen with the Van Slyke method. The specific rotation, after removal of the picric acid, was +10° while the specific rotation of natural octopine is +20°.