Phenylphennanthridines with PDE-IV inhibiting activity

A compound of formula I,

• in which
• R1 is hydroxyl, 1-4C-alkoxy, 3-7C-cycloalkoxy, 3-7C-cycloalkylmethoxy or completely or predominantly fluorine-substituted 1-4C-alkoxy,
• R2 is hydroxyl, 1-4C-alkoxy, 3-7C-cycloalkoxy, 3-7C-cycloalkylmethoxy or completely or predominantly fluorine-substituted 1-4C-alkoxy,
• or in which
• R1 and R2 together are a 1-2C-alkylenedioxy group,
• R3 is hydrogen or 1-4C-alkyl,
• R31 is hydrogen or 1-4C-alkyl,
• or in which
• R3 and R31 together are a 1-4C-alkylene group,
• R4 is hydrogen or 1-4C-alkyl,
• R5 is hydrogen,
• R51 is hydrogen,
• or in which
• R5 and R51 together represent an additional bond,
• R6 is O-R7, S—R8, C(O)—R9, CH2—R10, S(O)2-aryl, O—S(O)2—R11, pyrrolidin-1-yl, pyrrolidin-1-yl-2-one, pyrrolidin-1-yl-2,5-dione, piperidin-1-yl, piperidin-1-yl-2-one or piperidin-1-yl-2,6-dione, where
• R7 is 3-7C-cycloalkyl, 3-7C-cycloalkylmethyl, 1-4C-alkoxy-1-4C-alkyl, aryl or phenyl-1-4C-alkyl,
• R8 is hydrogen, 1-4C-alkyl, 1-4C-alkylcarbonyl, arylcarbonyl, trifluoromethyl, difluoromethyl, trichloromethyl or phenyl,
• R9 is 1-4C-alkyl, 3-7C-cycloalkyl, 3-7C-cycloalkylmethyl, 1-pyrrolidinyl, 1-piperidinyl, 1-piperazinyl, 4-methylpiperazinyl, 4-morpholinyl or aryl,
• R10 is hydroxyl, halogen, cyano, carboxyl, 1-4C-alkoxy, phenoxy, 1-4C-alkoxycarbonyl, aminocarbonyl, mono- or di-1-4C-alkylaminocarbonyl, N(R15)R16 or 1-4C-alkylcarbonylamino, and
• R11 is 1-4C-alkyl, amino, mono- or di-1-4C-alkylamino or aryl, aryl is phenyl, pyridyl or R12-substituted phenyl, where
• R12 is hydroxyl, halogen, carboxyl, nitro, amino, cyano, 1-4C-alkyl, trifluoromethyl, 1-4C-alkoxy, 1-4C-alkoxycarbonyl, 1-4C-alkylcarbonylamino, 1-4C-alkylcarbonyloxy or aminocarbonyl,
• R13 is hydrogen, hydroxyl, halogen, cyano, nitro, amino, 1-4C-alkyl, trifluoromethyl, 1-4C-alkoxy, completely or predominantly fluorine-substituted 1-4C-alkoxy, phenyl, phenyl-1-4C-alkyl, C(O)—OR14, C(O)—N (R15)R16, N(R17)R18, S(O)2—R19, S(O)2—N(R15)R16 or has one of the meanings of R6, where
• R14 is hydrogen, 1-4C-alkyl, 3-7C-cycloalkyl or 3-7C-cycloalkylmethyl,
• R15 is hydrogen, 1-4C-alkyl, 3-7C-cycloalkyl or 3-7C-cycloalkylmethyl,
• R16 is hydrogen, 1-4C-alkyl, 3-7C-cycloalkyl, 3-7C-cycloalkylmethyl or aryl,
• or where R15 and R16, together and including the nitrogen atom to which both are bonded, represent a 1-pyrrolidinyl, 1-piperidinyl, 1-piperazinyl, 4-methylpiperazin-1-yl, 1-hexahydroazepinyl or 4-morpholinyl radical,
• R17 is hydrogen, 1-4C-alkyl, S(O)2—R19 or S(O)2-aryl,
• R18 is 1-4C-alkyl, 1-4C-alkylcarbonyl, 3-7C-cycloalkylcarbonyl, 3-7C-cycloalkylmethylcarbonyl, S(O)2—R19 or S(O)2-aryl, and
• R19 is 1-4C-alkyl,
• R20 is hydrogen, hydroxyl, halogen, nitro, amino, 1-4C-alkyl, trifluoromethyl, 1-4C-alkoxy, completely or predominantly fluorine-substituted 1-4C-alkoxy, 3-7C-cycloalkoxy, 3-7C-cycloalkylmethoxy, CH2—R10, carboxyl, 1-4C-alkoxycarbonyl, 1-4C-alkylcarbonyloxy, 1-4C-alkylcarbonylamino or aminocarbonyl,
• or a pharmaceutically acceptable salt, an N-oxide, or a salt of an N-oxide of this compound.