The structures of compounds (I) and (II) are shown in Fig. 1 with erratums: compounds (I) and (II) should contain pyridine rings, but they were given with phenolic ones. The correct structures are shown in the corrected version of the Fig. 1.

Fig. 1.
figure 1

Structures of test ((I) and (II)) and reference (CUR, DZG) compounds.