Analgesic compounds are of the general formula (I):
in which, R¹ and R² each represents hydrogen or C₁-C₆ alkyl, or R¹ and R² together with the nitrogen atom to which they are attached form a heterocycle; E represents methylene, sulphur, oxygen or imino group optionally substituted with C₁-C₆ alkyl or aralkyl; ring A is aryl or heteroaryl ring, optionally substituted; R³ is hydrogen or C₁-C₆ alkyl and R⁴ is hydrogen or R³ and R⁴ together represent a group of formula (IV):
-(CRaRa)m-C(=Y)- (IV)
(wherein Ra and Ra is C₁-C₆ alkyl or hydrogen, up to a maximum of 3 alkyl groups, m is 1, 2, or 3, and Y is two hydrogens or oxygen); provided that when E represents a methylene group, then R³ is a C₁-C₆ alkyl group or R³ and R⁴ together represent a group of the formula (IV).