Compounds of formula I ##STR1## in which R1, R2, R3, R4a, R4b, R5a, R5b, R6 and R7 have the meanings indicated in the specification, and their pharmacologically tolerable salts are useful for preventing and/or treating gastrointestinal diseases.

I residui del ## del ## STR1 di formula I in cui R1, R2, R3, R4a, R4b, R5a, R5b, R6 e R7 hanno i significati hanno indicato in specifica e loro sali farmacologicamente tollerabili sono utili per impedire e/o trattare le malattie gastrointestinali.