Compounds of general formula in which R denotes a benzyl, 2-fluorobenzyl, 3-fluorobenzyl, 4-fluorobenzyl, 2,6-difluoro-benzyl, 3,4-difluoro-benzyl, 2-chlorobenzyl, 3-chlorobenzyl or 4-chlorobenzyl group, a 2-trifluoromethyl-benzyl, 3-trifluoromethyl-benzyl or 4-trifluoromethyl-benzyl group, a 3-trifluoromethoxy-benzyl or 4-trifluoromethoxy-benzyl group, a 2-cyanobenzyl, 3-cyanobenzyl or 4-cyanobenzyl group, a 2,6-dicyanobenzyl, 3,4-dicyanobenzyl, 3,5-dicyanobenzyl, 2-trifluoromethyl-4-cyanobenzyl, 3-nitro-4-cyano-benzyl, 2-cyano-3-methoxy-benzyl, 2-cyano-4-methoxy-benzyl, 2-cyano-5-methoxy-benzyl, 2-cyano-4-fluoro-benzyl, 2-cyano-5-fluoro-benzyl, 2-cyano-6-fluoro-benzyl, 3-cyano-4-fluoro-benzyl, 4-cyano-3-fluoro-benzyl, 2-fluoro-4-cyano-benzyl, 2-cyano-3-chlorobenzyl, 2-chloro-4-cyano-benzyl or 2-cyano-4-bromobenzyl group, a 2-methoxy-benzyl, 3-methoxy-benzyl, 4-methoxy-benzyl, 2-fluoro-3-methoxy-benzyl, 2-fluoro-4-methoxy-benzyl, 2-fluoro-5-methoxy-benzyl, 3-fluoro-4-methoxy-benzyl, 3,4-dimethoxy-benzyl, 3,5-dimethoxybenzyl or 3,4-dimethoxy-6-fluoro-benzyl group, a (benzo[1,3]dioxol-5-yl)methyl group, a [(4-cyano-benzo[1,3]dioxol-5-yl)methyl group, a 2-(3-cyclopropyloxy-phenyl)-2-oxo-ethyl, 2-(3-cyclopropylmethoxy-phenyl)-2-oxo-ethyl or 2-(3-cyclobutyloxy-phenyl)-2-oxo-ethyl group, a 2-oxo-2-[2-(pyridin-3-yl)-phenyl]-ethyl or 2-oxo-2-[2-(pyridin-4-yl)-phenyl]-ethyl group, a (3-cyano-naphthalen-1-yl)methyl, (1,4-dicyano-naphthalen-2-yl)methyl or (2,4-dimethoxy-naphthalen-1-yl)methyl group, a (furan-2-yl)methyl, (furan-3-yl)methyl, (5-bromo-furan-2-yl)methyl, (5-methyl-furan-2-yl)methyl, (5-cyano-furan-2-yl)methyl or (5-methoxycarbonyl-furan-2-yl)methyl group, a (pyridin-2-yl)methyl, (6-fluoro-pyridin-2-yl)methyl or (5-methoxy-pyridin-2-yl)methyl group, a (3-cyanopyridin-2-yl)methyl, (6-cyanopyridin-2-yl)methyl, (5-cyano-pyridin-2-yl)methyl, (4-cyano-pyridin-2-yl)methyl, (4-cyano-pyridin-3-yl)methyl, (3-cyano-pyridin-4-yl)methyl, (2-cyano-pyridin-3-yl)methyl, (2-cyano-pyridin-4-yl)methyl, (5-cyano-pyridin-3-yl)methyl, (6-cyano-pyridin-3-yl)methyl or (5-cyano-6-methoxy-pyridin-2-yl)methyl group, a (6-phenyl-pyridin-2-yl)methyl or a ([2,2']bipyridinyl-6-yl)methyl group, a (pyrimidin-2-yl)methyl, (4-methyl-pyrimidin-2-yl)methyl or (4,6-dimethyl-pyrimidin-2-yl)methyl group, a (2-phenyl-pyrimidin-4-yl)methyl or (4-phenyl-pyrimidin-2-yl)methyl group, a [(1-methyl-1H-benzotriazol-5-yl)methyl] group, a (6-fluoro-quinolin-2-yl)methyl, (7-fluoro-quinolin-2-yl)methyl, (2-methyl-quinolin-4-yl)methyl, (3-cyano-quinolin-2-yl)methyl, (3-cyano-4-methyl-quinolin-2-yl)methyl, (4-cyano-quinolin-2-yl)methyl, (5-cyano-quinolin-2-yl)methyl, (8-cyano-quinolin-2-yl)methyl, (6-amino-quinolin-2-yl)methyl, (8-amino-quinolin-2-yl)methyl, (4-methoxy-quinolin-2-yl)methyl, (6-methoxy-quinolin-2-yl)methyl, (6,7-dimethoxy-quinolin-2-yl)methyl or (8-cyano-quinolin-7-yl)methyl group, a (1-cyano-isoquinolin-3-yl)methyl, (4-cyano-isoquinolin-1-yl)methyl, (4-cyano-isoquinolin-3-yl)methyl or [(4-(pyridin-2-yl)-isoquinolin-1-yl]methyl group, a (quinazolin-6-yl)methyl, (quinazolin-7-yl)methyl, (2-methyl-quinazolin-4-yl)methyl, (4,5-dimethyl-quinazolin-2-yl)methyl, (4-ethyl-quinazolin-2-yl)methyl, (4-cyclopropyl-quinazolin-2-yl)methyl, (2-phenyl-quinazolin-4-yl)methyl, (4-cyano-quinazolin-2-yl)methyl, (4-phenylamino-quinazolin-2-yl)methyl or (4-benzylamino-quinazolin-2-yl)methyl group, a (quinoxalin-5-yl)methyl, (quinoxalin-6-yl)methyl or (2,3-dimethyl-quinoxalin-6-yl)methyl group, or a ([1,5]naphthyridin-3-yl)methyl group, the tautomers, enantiomers, diastereomers thereof, the mixtures thereof and the salts thereof, for use in the prevention or treatment of diseases or conditions which are linked to increased DPP-IV activity or can be influenced by inhibiting DPP-IV activity, in particular of type I or type II diabetes mellitus or a diabetic complication, wherein said compounds of formula, the tautomers, enantiomers, diastereomers thereof, the mixtures thereof or the salts thereof are optionally used in combination with other active ingredients.