A compound having the structure wherein n is 0 or 1; R 1 is selected from the group consisting of linear or branched C 1 -C 8 alkyl, oxetanyl, tetrahydrofuranyl, tetrathydropyranyl and saturated monocyclic C 3 -C 8 cycloalkyl; or R 1 is selected from the group consisting of oxetanyl substituted one or two times with methyl or hydroxy; tetrahydrofuranyl substituted one or two times with methyl or hydroxy; tetrathydropyranyl substituted one or two times with methyl or hydroxy; saturated monocyclic C 3 -C 8 cycloalkyl substituted one or two times with methyl or hydroxy; and linear or branched C 1 -C 8 alkyl substituted one, two or three times with fluorine; and R 2 is selected from the group consisting of linear or branched C 1 -C 8 alkyl, phenyl, saturated monocyclic C 3 -C 8 cycloalkyl, saturated bicyclic C 4 -C 10 cycloalkyl, saturated tricyclic C 7 -C 10 cycloalkyl, oxetanyl, tetrahydrofuranyl and tetrahydropyranyl; or R 2 is selected from the group consisting of phenyl substituted with a substituent selected from the group consisting of halogen, methyl, difluoromethyl, trifluoromethyl and methoxy; saturated monocyclic C 3 -C 8 cycloalkyl, substituted one or two times with substituents selected from the group consisting of fluorine and methyl; and oxetanyl, tetrahydrofuranyl and tetrahydropyranyl, each substituted one or two times with substituents selected from the group consisting of fluorine and methyl; R 3 is selected from the group consisting of hydrogen, linear or branched C 1 -C 4 alkyl, phenyl, substituted phenyl, halogen and tetrahydrofuranyl; R 4 is selected from the group consisting of hydrogen, linear or branched C 1 -C 4 alkyl, halogen, and tetrahydrofuranyl; and pharmaceutically acceptable acid addition salts of Compound I, racemic mixtures of Compound I, or the corresponding enantiomer and/or optical isomer of Compound I, and polymorphic forms of Compound I as well as tautomeric forms of Compound I; with the proviso that compound I is not 1,2,4-Triazolo[4,3-a]pyrazin-8 -one, 7-[(4-chlorophenyl)methyl]-3-methyl- (CAS Registry Number: 946270-18-4) or 1,2,4-Triazolo[4,3-a]pyrazin-8 -one, 7-[(4-chlorophenyl)methyl]-3-propyl- (CAS Registry Number: 946237-23-6). n is 0 or 1; R 1 is selected from the group consisting of linear or branched C 1 -C 8 alkyl, oxetanyl, tetrahydrofuranyl, tetrathydropyranyl and saturated monocyclic C 3 -C 8 cycloalkyl; or R 1 is selected from the group consisting of oxetanyl substituted one or two times with methyl or hydroxy; tetrahydrofuranyl substituted one or two times with methyl or hydroxy; tetrathydropyranyl substituted one or two times with methyl or hydroxy; saturated monocyclic C 3 -C 8 cycloalkyl substituted one or two times with methyl or hydroxy; and linear or branched C 1 -C 8 alkyl substituted one, two or three times with fluorine; and R 2 is selected from the group consisting of linear or branched C 1 -C 8 alkyl, phenyl, saturated monocyclic C 3 -C 8 cycloalkyl, saturated bicyclic C 4 -C 10 cycloalkyl, saturated tricyclic C 7 -C 10 cycloalkyl, oxetanyl, tetrahydrofuranyl and tetrahydropyranyl; or R 2 is selected from the group consisting of phenyl substituted with a substituent selected from the group consisting of halogen, methyl, difluoromethyl, trifluoromethyl and methoxy; saturated monocyclic C 3 -C 8 cycloalkyl, substituted one or two times with substituents selected from the group consisting of fluorine and methyl; and oxetanyl, tetrahydrofuranyl and tetrahydropyranyl, each substituted one or two times with substituents selected from the group consisting of fluorine and methyl; R 3 is selected from the group consisting of hydrogen, linear or branched C 1 -C 4 alkyl, phenyl, substituted phenyl, halogen and tetrahydrofuranyl; R 4 is selected from the group consisting of hydrogen, linear or branched C 1 -C 4 alkyl, halogen, and tetrahydrofuranyl; and pharmaceutically acceptable acid addition salts of Compound I, racemic mixtures of Compound I, or the corresponding enantiomer and/or optical isomer of Compound I, and polymorphic forms of Compound I as well as tautomeric forms of Compound I; with the proviso that compound I is not 1,2,4-Triazolo[4,3-a]pyrazin-8 -one, 7-[(4-chlorophenyl)methyl]-3-methyl- (CAS Registry Number: 946270-18-4) or 1,2,4-Triazolo[4,3-a]pyrazin-8 -one, 7-[(4-chlorophenyl)methyl]-3-propyl- (CAS Registry Number: 946237-23-6).