title: Stereochemistry of the incorporation of valine methyl groups into methylene groups in cephalosporin C.
abstract: 'Chiral methyl valines', i.e. samples of valine labelled stereospecifically in the methyl groups with 2H and 3H, were incorporated into cephalosporin C by a suspension of washed cells of Cephalosporium acremonium. Analysis by 3H n.m.r. of the cephalosporin C produced showed that the conversion of the 3-pro-S-methyl group of valine into the acetoxymethyl side-chain was a highly stereospecific process. By contrast, conversion of the 3-pro-R-methyl group into the endocyclic methylene group of the dihydrothiazine ring was shown to proceed by a non-stereospecific process.
mesh_terms: D000164:Acremonium / Q000378:metabolism*; D002511:Cephalosporins / Q000096:biosynthesis* / Q000302:isolation & purification; D055598:Chemical Phenomena; D002621:Chemistry; D003903:Deuterium; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D014316:Tritium; D014633:Valine / Q000378:metabolism
chemical_list: D002511:Cephalosporins; D014316:Tritium; C025163:cephalosporin C; D003903:Deuterium; D014633:Valine