Synthesis of labeled 3-Hydroxyproline and biosynthesis of the Dehydroproline Moiety of Virginiamycin M₁
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(R,S)Â·[CarboxylÂ·4C]Â·cis-3-hydroxyproline was synthesized from S-[carboxylÂ·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)-[caboxy1Â·14C]-cis-3-acetoxyproline which was hydrolyzed with hydrochloric acid and purified by ion-exchange chromatography and recrystallization. In order to determine if cisÂ·3-hydroxyproline is a precursor for the dehydroproline moiety of virginiamycin M1, (R,S)-[carboxy1-14C ]-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.
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