Fig. 9. 13C NMR spectrum (CDCl3) of Ac-His-6-MBHA-1e obtained by reaction of Ac-His-6 with a ten-fold excess of 1e compared with that of Ac-His-6-MBHA-1d obtained by reaction of Ac-His-6 with a ten-fold excess of 1d. The peaks marked by 9 were attributed to compound 9, which was produced in the concerted addition–elimination process and remained as a counterion of the imidazolium salt moieties.
