A compound of formula 1 wherein: A is a group selected from X− is an anion with a single negative charge; R1 and R2 are each independently a C1-C4-alkyl optionally substituted with hydroxy or halogen; and R3, R4, R5, R6, R7, and R8 are each independently hydrogen, C1-C4-alkyl, C1-C4-alkyloxy, hydroxy, CF3, CN, NO2, or halogen, with the proviso that at least one of the groups R3, R4, R5, R6, R7, and R8 is not hydrogen, processes for preparing these compounds, pharmaceutical compositions containing these compounds, and their use as pharmaceutical compositions.