| Abstrakt: |
The title compound was synthesized by exchange of dimethylpyruvic acid with NaOH–HTO, followed by reductive amination using cyanoborohydride in methanol solvent, resolution of the N-chloroacetyl derivative, and admixture with [U-14C]-L-valine. Degradation of the compound revealed that 94.5% of the tritium was attached to C3, and 5.5% was located on the methyl groups. Incorporation of this doubly labelled valine into penicillin V, purified as the dibenzylamine salt, proceeded with 100.7% loss of the tritium originally present at C3. Commercial [2,3-3H, U-14C]-L-valine, which was found to have 12% of the tritium on the methyl groups, was also incorporated into penicillin V, purified as its methyl ester. Degradation to remove the hydrogen attached to C3 of this ester revealed that no tritium was present at this position. Therefore, in agreement with an earlier result and other related studies, the β-hydrogen of valine is not transferred to C3 of penicillin during the biosynthesis of the latter compound. |
