A compound of formula: wherein n is 1 or 2; R 1 is hydrogen or an alkyl, alkenyl, alkynyl, heteroalkyl, cycloalkyl, heterocycloalkyl, alkylcycloalkyl, heteroalkylcycloalkyl, aryl, heteroaryl, aralkyl or heteroaralkyl group, all of which groups may optionally be substituted; R 2 is hydrogen or an alkyl, alkenyl, alkynyl, heteroalkyl, cycloalkyl, heterocycloalkyl, alkylcycloalkyl, heteroalkylcycloalkyl, aryl, heteroaryl, aralkyl or heteroaralkyl group, all of which groups may optionally be substituted, and R 3 is hydrogen; or R 2 and R 3 together are part of an optionally substituted heterocycloalkyl or heteroaryl group; and R 4 is hydrogen or methyl, or a pharmaceutically acceptable salt, solvate or hydrate or a pharmaceutically acceptable formulation thereof; wherein the expression alkyl refers to a saturated, straight-chain or branched hydrocarbon group that contains from 1 to 20 carbon atoms; furthermore, the term alkyl refers to groups in which one or more hydrogen atoms have been replaced by a halogen atom; the expressions alkenyl and alkynyl refer to at least partially unsaturated, straight-chain or branched hydrocarbon groups that contain from 2 to 20 carbon atoms; furthermore, the terms alkenyl and alkynyl refer to groups in which one or more hydrogen atoms have been replaced by a halogen atom; the expression heteroalkyl refers to an alkyl, alkenyl or alkynyl group in which one or more carbon atoms have been replaced by an oxygen, nitrogen, phosphorus, boron, selenium, silicon or sulfur atom or a group of formula SO or SO 2; furthermore, the term heteroalkyl refers to groups in which one or more hydrogen atoms have been replaced by a halogen atom; the expression cycloalkyl refers to a saturated or partially unsaturated cyclic group that contains one or more rings, and contains from 3 to 14 ring carbon atoms; the expression cycloalkyl refers furthermore to groups in which one or more hydrogen atoms have been replaced by fluorine, chlorine, bromine or iodine atoms or by OH, =O, SH, =S, NH 2, =NH, N 3 or NO 2 groups, the expression heterocycloalkyl refers to a cycloalkyl group as defined above in which one or more ring carbon atoms have been replaced by an oxygen, nitrogen, silicon, selenium, phosphorus or sulfur atom; the expression heterocycloalkyl refers furthermore to groups that may be substituted by one or more fluorine, chlorine, bromine or iodine atoms or by one or more OH, =O, SH, =S, NH 2, =NH, N 3 or NO 2 groups; the expression alkylcycloalkyl refers to groups that contain both cycloalkyl and also alkyl, alkenyl or alkynyl groups in accordance with the above definitions; and the expression heteroalkylcycloalkyl refers to alkylcycloalkyl groups as defined above in which one or more carbon atoms have been replaced by an oxygen, nitrogen, silicon, selenium, phosphorus or sulfur atom. n is 1 or 2; R 1 is hydrogen or an alkyl, alkenyl, alkynyl, heteroalkyl, cycloalkyl, heterocycloalkyl, alkylcycloalkyl, heteroalkylcycloalkyl, aryl, heteroaryl, aralkyl or heteroaralkyl group, all of which groups may optionally be substituted; R 2 is hydrogen or an alkyl, alkenyl, alkynyl, heteroalkyl, cycloalkyl, heterocycloalkyl, alkylcycloalkyl, heteroalkylcycloalkyl, aryl, heteroaryl, aralkyl or heteroaralkyl group, all of which groups may optionally be substituted, and R 3 is hydrogen; or R 2 and R 3 together are part of an optionally substituted heterocycloalkyl or heteroaryl group; and R 4 is hydrogen or methyl, or a pharmaceutically acceptable salt, solvate or hydrate or a pharmaceutically acceptable formulation thereof; wherein the expression alkyl refers to a saturated, straight-chain or branched hydrocarbon group that contains from 1 to 20 carbon atoms; furthermore, the term alkyl refers to groups in which one or more hydrogen atoms have been replaced by a halogen atom; the expressions alkenyl and alkynyl refer to at least partially unsaturated, straight-chain or branched hydrocarbon groups that contain from 2 to 20 carbon atoms; furthermore, the terms alkenyl and alkynyl refer to groups in which one or more hydrogen atoms have been replaced by a halogen atom; the expression heteroalkyl refers to an alkyl, alkenyl or alkynyl group in which one or more carbon atoms have been replaced by an oxygen, nitrogen, phosphorus, boron, selenium, silicon or sulfur atom or a group of formula SO or SO 2; furthermore, the term heteroalkyl refers to groups in which one or more hydrogen atoms have been replaced by a halogen atom; the expression cycloalkyl refers to a saturated or partially unsaturated cyclic group that contains one or more rings, and contains from 3 to 14 ring carbon atoms; the expression cycloalkyl refers furthermore to groups in which one or more hydrogen atoms have been replaced by fluorine, chlorine, bromine or iodine atoms or by OH, =O, SH, =S, NH 2, =NH, N 3 or NO 2 groups, the expression heterocycloalkyl refers to a cycloalkyl group as defined above in which one or more ring carbon atoms have been replaced by an oxygen, nitrogen, silicon, selenium, phosphorus or sulfur atom; the expression heterocycloalkyl refers furthermore to groups that may be substituted by one or more fluorine, chlorine, bromine or iodine atoms or by one or more OH, =O, SH, =S, NH 2, =NH, N 3 or NO 2 groups; the expression alkylcycloalkyl refers to groups that contain both cycloalkyl and also alkyl, alkenyl or alkynyl groups in accordance with the above definitions; and the expression heteroalkylcycloalkyl refers to alkylcycloalkyl groups as defined above in which one or more carbon atoms have been replaced by an oxygen, nitrogen, silicon, selenium, phosphorus or sulfur atom.