Figure 7.

Stepwise OMPDC-catalyzed decarboxylation of OMP (X= H, bottom reaction) and the exchange reaction of -H from FUMP for -D from solvent D₂O (X = F, top reaction). The inequality k_p ≫ k_rot for partitioning of the vinyl carbanion intermediate between proton transfer and bond rotation at the K93 side chain ensures that the deuterium enrichment of product of OMPDC-catalyzed decarboxylation of OMP is equal to the initial 50% enrichment of the mixed H₂O/D₂O solvent,^62,63 and that the barrier to the deprotonation of FUMP (ΔG_dp^‡) is smaller than the overall barrier for the deuterium exchange reaction.