Fig. 5. 1H NMR spectrum (500 MHz, CDCl3) of Ac-His-6-MBHA-1d obtained by reaction of Ac-His-6 with a ten-fold excess of 1d compared with that of biadduct 3c. 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.
