A compound of formula wherein - the methyl group at position 12 of the mutilin ring has the inverse stereochemistry compared with the stereochemistry of the methyl group at position 12 of the naturally occurring pleuromutilin ring, - all other substituents of the mutilin ring having the same stereochemistry compared with the stereochemistry of the substituents at the corresponding positions in the naturally occurring pleuromutilin ring, R 1 is either (C 1-16)alkyl or (C 2-16)alkenyl, substituted by heterocyclyl, including aliphatic heterocyclyl and aromatic heterocyclyl comprising 1 to 4 heteroatoms selected from N, O, S, with the proviso that at least one heteroatom is a nitrogen atom, or R 1 is a group of formula wherein Y-N(R 3 R 4) is - (C 1-16)alkyl-N(R 3 R 4), - (C 1-16)alkyl-(C 6-14)aryl-N(R 3 R 4), - (C 1-16)alkyl-(C 6-14)aryl-(C 1-16)alkyl-N(R 3 R 4), - (C 1-16)alkyl-(C 1-13)heterocyclyl -N(R 3 R 4), - (C 1-16)alkyl-(C 1-13)heterocyclyl-(C 1-16)alkyl-N(R 3 R 4), - carbonyl-N(R 3 R 4), - (C 1-4)alkyl-carbonyl-N(R 3 R 4), - (C 2-16)alkenyl-N(R 3 R 4), - (C 2-16)alkenyl-(C 6-14)aryl-N(R 3 R 4), - (C 2-16)alkenyl-(C 6-14)aryl-(C 1-16)alkyl-N(R 3 R 4), - (C 2-16)alkenyl-(C 1-13)heterocyclyl-N(R 3 R 4), - (C 2-16)alkenyl-(C 1-13)heterocyclyl-(C 1-16)alkyl-N(R 3 R 4), wherein heterocyclyl includes aliphatic and aromatic heterocyclyl comprising at least one heteroatom selected from N, O, S and wherein alkyl, aryl, heterocyclyl or alkenyl is optionally substituted comprising substituents which optionally having heteroatoms selected from O, N, S, halogen; R 3 and R 4 independently of each other are - hydrogen, - (C 1-16)alkyl, - (C 2-16)alkenyl, - hydroxy(C 1-16)alkyl, - amino-(C 1-16)alkyl, - mono or di-(C 1-6)alkylamino-(C 1-16)alkyl, - guanidino(C 1-16)a l kyl, ureido(C 1-16)alkyl or thioureido(C 1-16)alkyl, - amino(C 1-6)alkyl-(C 6-14)aryl-(C 1-6)alkyl, - amino(C 1-6)alkyl-(C 6-14)aryl, - guanidino(C 1-6)alkyl-(C 6-14)aryl-(C 1-6)alkyl, - amino-(C 1-6)alkyloxy-(C 1-6)alkyl, - amino(C 3-8)cycloalkyl, - amino(C 1-6)alkyl-(C 3-8)cycloalkyl, - amino(C 3-8)cycloalkyl-(C 1-6)alkyl, - amino(C 1-6)alkyl-(C 3-8)cycloalkyl-(C 1-6)alkyl, - (C 1-13)heterocyclyl-(C 1-16)alkyl, - (C 6-14)aryl-(C 1-16)alkyl, - (C 1-13)heterocyclyl, - amino-(C 6-14)aryl-(C 1-16)alkyl, - amino-(C 1-6)alkyloxy-(C 6-14)aryl-(C 1-6)alkyl, - amino(C 1-6)alkyl-(C 6-12)aryl-carbonyl, - amino(C 1-6)alkyl-amido-(C 6-12)aryl(C 1-6)alkyl, - (C 1-4)alkylcarbonyl, - carbamimidoyl, carbamoyl, thiocarbamoyl, wherein heterocyclyl includes aliphatic and aromatic heterocyclyl comprising at least one heteroatom selected from N, O, S, and wherein alkyl, cycloalkyl, heterocyclyl, alkenyl or aryl is optionally further substituted, by - amino(C 1-4)alkyl, amido, mono or di-(C 1-4)alkyl-amido, (C 1-6)alkyloxy-carbonyl, halogen, oxo, hydroxy X is sulfur or oxygen, in particular sulfur, and R 2 is a hydrocarbon group comprising 1 to 22 carbon atoms, optionally comprising heteroatoms selected from N, O, S, halogen, in particular N or O, optionally - in the form of a salt and/or solvate, in particular in the form of a salt, wherein the naturally occurring pleuromutilin is of formula - the methyl group at position 12 of the mutilin ring has the inverse stereochemistry compared with the stereochemistry of the methyl group at position 12 of the naturally occurring pleuromutilin ring, - all other substituents of the mutilin ring having the same stereochemistry compared with the stereochemistry of the substituents at the corresponding positions in the naturally occurring pleuromutilin ring, - (C 1-16)alkyl-N(R 3 R 4), - (C 1-16)alkyl-(C 6-14)aryl-N(R 3 R 4), - (C 1-16)alkyl-(C 6-14)aryl-(C 1-16)alkyl-N(R 3 R 4), - (C 1-16)alkyl-(C 1-13)heterocyclyl -N(R 3 R 4), - (C 1-16)alkyl-(C 1-13)heterocyclyl-(C 1-16)alkyl-N(R 3 R 4), - carbonyl-N(R 3 R 4), - (C 1-4)alkyl-carbonyl-N(R 3 R 4), - (C 2-16)alkenyl-N(R 3 R 4), - (C 2-16)alkenyl-(C 6-14)aryl-N(R 3 R 4), - (C 2-16)alkenyl-(C 6-14)aryl-(C 1-16)alkyl-N(R 3 R 4), - (C 2-16)alkenyl-(C 1-13)heterocyclyl-N(R 3 R 4), - (C 2-16)alkenyl-(C 1-13)heterocyclyl-(C 1-16)alkyl-N(R 3 R 4), - hydrogen, - (C 1-16)alkyl, - (C 2-16)alkenyl, - hydroxy(C 1-16)alkyl, - amino-(C 1-16)alkyl, - mono or di-(C 1-6)alkylamino-(C 1-16)alkyl, - guanidino(C 1-16)a l kyl, ureido(C 1-16)alkyl or thioureido(C 1-16)alkyl, - amino(C 1-6)alkyl-(C 6-14)aryl-(C 1-6)alkyl, - amino(C 1-6)alkyl-(C 6-14)aryl, - guanidino(C 1-6)alkyl-(C 6-14)aryl-(C 1-6)alkyl, - amino-(C 1-6)alkyloxy-(C 1-6)alkyl, - amino(C 3-8)cycloalkyl, - amino(C 1-6)alkyl-(C 3-8)cycloalkyl, - amino(C 3-8)cycloalkyl-(C 1-6)alkyl, - amino(C 1-6)alkyl-(C 3-8)cycloalkyl-(C 1-6)alkyl, - (C 1-13)heterocyclyl-(C 1-16)alkyl, - (C 6-14)aryl-(C 1-16)alkyl, - (C 1-13)heterocyclyl, - amino-(C 6-14)aryl-(C 1-16)alkyl, - amino-(C 1-6)alkyloxy-(C 6-14)aryl-(C 1-6)alkyl, - amino(C 1-6)alkyl-(C 6-12)aryl-carbonyl, - amino(C 1-6)alkyl-amido-(C 6-12)aryl(C 1-6)alkyl, - (C 1-4)alkylcarbonyl, - carbamimidoyl, carbamoyl, thiocarbamoyl, - amino(C 1-4)alkyl, amido, mono or di-(C 1-4)alkyl-amido, (C 1-6)alkyloxy-carbonyl, halogen, oxo, hydroxy - in the form of a salt and/or solvate, in particular in the form of a salt,