Sino-atrial node modulating pyrrolopyrimidines

A compound of formula I or a pharmaceutically-acceptable salt thereof, ##STR3## wherein:

• R.sup.1 is hydrogen, (1-8C)alkyl or phenyl(1-4C)alkyl;
• R.sup.2 is methyl;
• R.sup.3 is hydrogen, (1-6C)alkyl, phenyl(1-4C), (3-6C)cycloalkyl, (3-6C)cycloalkyl(1-4C)alkyl, phenyl or (3-6C)alkenyl;
• R.sup.4 and R.sup.5 are independently selected from hydrogen and (1-6C)alkyl;
• and wherein the phenyl ring shown in formula I and/or one or more of said phenyl moieties recited as R.sup.1 or R.sup.3 may optionally be unsubstituted or substituted by one or more substituents independently selected from halogen, (1-4C)alkyl, (3-6C)alkenyl, (1-4)alkoxy, cyano, trifluoromethyl, nitro, carboxy, (1-4C)alkylamino, dialkylamino of up to six carbon atoms, (1-4C)alkylthio, (1-4C)alkylsulphinyl, (1-4C)alkylsulphonyl and (1-4C)alkylenedioxy.

A method of modulating the action of the sino-atrial node in a warm-blooded animal requiring such treatment which comprises administering to said animal an effective amount of a pharmacologically active agent comprising a compound of the formula I or a pharmaceutically-acceptable salt thereof, ##STR4## wherein:

• R.sup.1 is hydrogen, (1-8C)alkyl or phenyl(1-4C)alkyl;
• R.sup.2 is (1-6C)alkyl, phenyl, phenyl(1-4C)alkyl, (3-6C)cycloalkyl or (3-6C)cycloalkyl(1-4C)alkyl;
• R.sup.3 is hydrogen, (1-6C)alkyl, phenyl(1-4C)alkyl, (3-6C)cycloalkyl, (3-6C)cycloalkyl(1-4C)alkyl, phenyl or (3-6C)alkenyl;
• R.sup.4 and R.sup.5 are independently selected from hydrogen and (1-6C)alkyl;
• and wherein the phenyl ring shown in formula I and/or one or more of said phenyl moieties recited as R.sup.1 or R.sup.3 may optionally be unsubstituted or substituted by one or more substituents independently selected from halogeno, (1-4C)alkyl, (3-6C)alkenyl, (1-4C)alkoxy, cyano, trifluoromethyl, nitro, carboxy, (1-4C)alkylamino, dialkylamino of up to six carbon atoms, (1-4C)alkythio, (1-4C)alkylsulphinyl, (1-4C)alkylsulphonyl and (1-4C)alkylenedioxy;
• but excluding the compound in which R.sup.1, R.sup.3, R.sup.4 and R.sup.5 are each methyl, the phenyl ring is unsubstituted and R.sup.2 is ethyl, and its pharmaceutically-acceptable salts.