group consisting of pyrrolidinyl, piperidinyl, piperazinyl and morpholino, and wherein the heterocyclic group has optionally a substituent selected from piperidinyl and a lower alkyl; and m is an integer of 0 to 3, a phenyl-lower alkoxycarbonyl, a lower alkanoyl, a phenyl-lower alkanoyl, a cycloalkyl-lower alkanoyl wherein said cycloalkyl group has 3 to 8 carbon atoms, a cycloalkyl-carbonyl wherei