A compound of the formula wherein R 1 and R 2 are the same or different and are selected from the group consisting of C 1-7 -alkyl, hydroxy-C 2-7 -alkyl, amino-C 2-7 -alkyl, C 2-7 -alkenyl and C 3-7 -alkynyl; R 3 is hydrogen or C 1-7 -alkyl; R 6 is hydrogen or C 1-7 -alkyl; one of R 4 and R 5 is selected from the group consisting of hydrogen, C 1-7 -alkyl, halogen-C 1-7 -alkyl and C 1-7 -alkoxy, and the other one of R 4 and R 5 is wherein R 7 and R 8 are the same or different and are selected from the group consisting of hydrogen, C 1-7 -alkyl, halogen-C 1-7 alkyl, hydroxy-C 1-7 alkyl, hydroxy-C 1-7 -alkoxy-C 1-7 -alkyl, amino-C 1-7 -alkyl, C 1-7 -alkyl-amino-C 1-7 -alkyl, amino-C 1-7 -alkoxy-C 1-7 -alkyl, C 1-7 -alkyl-amino-C 1-7 -alkoxy-C 1-7 -alkyl, amino-C 1-7 -alkyl-carbonyl and C 1-7 -alkyl-amino-C 1-7 -alkyl-carbonyl, or R 7 and R 8 together with the nitrogen atom they are attached to form a 4- to 6-membered heterocycle which is unsubstituted or substituted with a group selected from the group consisting of amino, C 1-7 -alkyl-amino, hydroxy and hydroxy-C 1-7 alkyl and which may contain an additional N-R 10 group, wherein R 10 is selected from the group consisting of hydrogen, amino-C 1-7 -alkyl and C 1-7 -alkyl-amino-C 1-7 -alkyl; Y is N or CR 9, wherein R 9 is selected from the group consisting of hydrogen, C 1-7 -alkyl and halogen-C 1-7 -alkyl; or its pharmaceutically acceptable salts. R 1 and R 2 are the same or different and are selected from the group consisting of C 1-7 -alkyl, hydroxy-C 2-7 -alkyl, amino-C 2-7 -alkyl, C 2-7 -alkenyl and C 3-7 -alkynyl; R 3 is hydrogen or C 1-7 -alkyl; R 6 is hydrogen or C 1-7 -alkyl; one of R 4 and R 5 is selected from the group consisting of hydrogen, C 1-7 -alkyl, halogen-C 1-7 -alkyl and C 1-7 -alkoxy, and the other one of R 4 and R 5 is wherein R 7 and R 8 are the same or different and are selected from the group consisting of hydrogen, C 1-7 -alkyl, halogen-C 1-7 alkyl, hydroxy-C 1-7 alkyl, hydroxy-C 1-7 -alkoxy-C 1-7 -alkyl, amino-C 1-7 -alkyl, C 1-7 -alkyl-amino-C 1-7 -alkyl, amino-C 1-7 -alkoxy-C 1-7 -alkyl, C 1-7 -alkyl-amino-C 1-7 -alkoxy-C 1-7 -alkyl, amino-C 1-7 -alkyl-carbonyl and C 1-7 -alkyl-amino-C 1-7 -alkyl-carbonyl, or R 7 and R 8 together with the nitrogen atom they are attached to form a 4- to 6-membered heterocycle which is unsubstituted or substituted with a group selected from the group consisting of amino, C 1-7 -alkyl-amino, hydroxy and hydroxy-C 1-7 alkyl and which may contain an additional N-R 10 group, wherein R 10 is selected from the group consisting of hydrogen, amino-C 1-7 -alkyl and C 1-7 -alkyl-amino-C 1-7 -alkyl; wherein R 7 and R 8 are the same or different and are selected from the group consisting of hydrogen, C 1-7 -alkyl, halogen-C 1-7 alkyl, hydroxy-C 1-7 alkyl, hydroxy-C 1-7 -alkoxy-C 1-7 -alkyl, amino-C 1-7 -alkyl, C 1-7 -alkyl-amino-C 1-7 -alkyl, amino-C 1-7 -alkoxy-C 1-7 -alkyl, C 1-7 -alkyl-amino-C 1-7 -alkoxy-C 1-7 -alkyl, amino-C 1-7 -alkyl-carbonyl and C 1-7 -alkyl-amino-C 1-7 -alkyl-carbonyl, or R 7 and R 8 together with the nitrogen atom they are attached to form a 4- to 6-membered heterocycle which is unsubstituted or substituted with a group selected from the group consisting of amino, C 1-7 -alkyl-amino, hydroxy and hydroxy-C 1-7 alkyl and which may contain an additional N-R 10 group, wherein R 10 is selected from the group consisting of hydrogen, amino-C 1-7 -alkyl and C 1-7 -alkyl-amino-C 1-7 -alkyl; Y is N or CR 9, wherein R 9 is selected from the group consisting of hydrogen, C 1-7 -alkyl and halogen-C 1-7 -alkyl;