Synthesis of Labeled 3-Hydroxyproline and Biosynthesis of the Dehydroproline Moiety of Virginiamycin M₁

(R,S)-[Carboxyl-¹⁴C]–cis-3-hydroxyproline was synthesized from S-[carboxyl-¹⁴C] proline. The oxygen functionality at the three position was obtained by acetylation of 1,2-dehydroproline methyl ester using lead tetraacetate. Reduction of the imine with sodium borohydride gave predominately (R,S)-[caboxyl-¹⁴C]-cis-3-acetoxyproline which was hydrolyzed with hydrochloric acid and purified by ion-exchange chromatography and recrystallization.

In order to determine if cis-3-hydroxyproline is a precursor for the dehydroproline moietyof virginiamycin M1, (R,S)-[carboxyl-¹⁴C]-cis-3-hydroxyproline and S-[3,4-³H] proline with a ³H/¹⁴C of 9 were fed simultaneously to a virginiamycin producing strain of Streptomyces. The resulting antibiotic had a ³H/¹⁴C ratio of 41.3. The proline portion of the antibiotic had a ratio of 19.9. Therefore, 45% of the cis-3-hydroxyproline was incorporated, and cis-3-hydroxyproline is a precursor to the dehydroproline moiety.