1,3-Prototropic hydrogen shift

Therefore, alternative pathways involving a formal 1,3-hydrogen shift were considered an electrophilic pathway (path II) and a deprotonation/protonation sequence (path III) (Scheme 14.21) [17]. Prototropic rearrangement (path II) is consistent with the effect of Lewis acidic additives. Moreover, substitution at the 2- and 4-positions of enyne (R H) would provide necessary cation stabilization, which is in... 

Although K258A mutant is considered to be a dead enzyme, it has shown a small residual transaminase activity. The stereochemical fidelity of the K258A mutant enzyme was examined by measuring the residual transamination reaction in which the labilization of the pro-S C-4 hydrogen of PMP was monitored.42 During the normal transamination reaction, it was observed that the a-proton of the substrate was trasferred to the pro-S C-4 positionof PMP and the same proton was removed from the pro-S C-4 position then transferred to the second substrate, a part of the 1,3-prototropic shift in the transamination... 

N-NMR spectroscopy is particularly useful in prototropic tautomerism studies (88JCS(P2)(ip)). With the changes in chemical shifts, which result when the NH hydrogen is replaced by a methyl group, it is possible to estimate the tautomeric composition of thiadiazines if the N-methyl derivatives corresponding to the possible tautomers are available (Section II,A,5). 

Therefore, the tautomerization process can be pictured as either an intramolecular (enzyme assisted) cis transfer or a trans transfer of hydrogen. This rearrangement is referred to as a tautomeric 1,3-prototropic shift and model studies have tried to solve this stereochemical ambiguity ... 

---