Bicyclic aza compounds as muscarinic m1 receptor antagonists

A compound of the formula:

• or a salt thereof, wherein:
• X1 and X2 are saturated hydrocarbon groups which together contain a total of five to nine carbon atoms and which link together such that the moiety:
• forms a bicyclic ring system;
• R1 is selected from 2-methylpropyl;
• 2,2-dimethylpropyl;
• tert-butyl;
• 2-methyl-but-2-yl;
• 2,3-dimethylbut-2-yl;
• cyclopropylmethyl;
• cyclobutylmethyl;
• cyclopentyl;
• cyclopentylmethyl;
• 1-methylcyclobutyl;
• 1-methylcyclopentyl;
• 1-methylcyclohexyl;
• 1-methylcyclopentylmethyl;
• cyclopropyl-prop-2-yl;
• 1-methylcyclobutylmethyl and 1-ethyl-cyclobutylmethyl groups;
• R2 is selected from hydrogen, methyl, ethyl and isopropyl;
• or R1 and R2 together with the nitrogen atom to which they are attached form a non-aromatic heterocyclic ring of four to nine ring members, wherein the heterocyclic ring may optionally contain a second heteroatom selected from O, N and S and oxidised forms thereof;
• and wherein the heterocyclic ring may optionally be substituted with one to six substitutents selected from C1-2 alkyl;
• fluorine;
• and cyano;
• R3 is selected from hydrogen, fluorine and methoxy;
• and
• R4 is a C1-6 non-aromatic hydrocarbon group which is optionally substituted with one to six fluorine atoms and wherein one or two, but not all, carbon atoms of the hydrocarbon group may optionally be replaced by a heteroatom selected from O, N and S and oxidised forms thereof.