Tritium nuclear magnetic resonance spectroscopy. Part 7. New information from the tritium distribution in biosynthetically labelled penicillic acid
3 H N.m.r. spectroscopy is used to determine directly the regio- and stereo-specificity of the labelling in penicillic acid, biosynthesised by Penicillium cyclopium from [3H]acetate, from [2-3H]malonate, and from [3,5-3H]orsellinic acid. In particular, the method reveals the specific labelling of the 5-methylene group—largely trans to C-methyl—and the partial loss of label from the 5-positions relative to the 3-position and from the 3-position relative to the C-methyl group. It thus provides new information, which needs to be incorporated in any detailed proposals concerning the biosynthetic pathway and the enzyme stereochemistry. Such detail was not available from previous studies involving the use of 14C and 13C as tracers.