Abstract: The invention relates to a compound of formula Ia or Ib wherein R1 represents —CO2R3, —COR4 or —R5, wherein R3 represents unsubstituted or substituted C1-C6 alkyl, R4 represents hydrogen, unsubstituted or substituted C1-C6 alkyl, and R5 represents hydrogen, unsubstituted or substituted C1-C6 alkyl, R2 represents —N+(R6)(R7)(R8)X? or a nitro group, wherein R6, R7, R8 independently of each other represent unsubstituted or substituted C1-C6 alkyl or unsubstituted or substituted —(CH2)n- with n=1 to 12 provided that at least two of the substituents R6R7R8 are C1-C6 alkyl, and X? represents a halide, sulphonate, unsubstituted or substituted acetate, sulphate, hydrogen sulphate, nitrate, perchlorate, or oxalate.

Abstract: The invention relates to a compound of formula Ia or Ib wherein R1 represents —CO2R3, —COR4 or —R5, wherein R3 represents unsubstituted or substituted C1-C6 alkyl, R4 represents hydrogen, unsubstituted or substituted C1-C6 alkyl, and R5 represents hydrogen, unsubstituted or substituted C1-C6 alkyl, R2 represents —N+(R6)(R7)(R8)X? or a nitro group, wherein R6, R7, R8 independently of each other represent unsubstituted or substituted C1-C6 alkyl or unsubstituted or substituted —(CH2)n- with n=1 to 12 provided that at least two of the substituents R6R7R8 are C1-C6 alkyl, and X? represents a halide, sulphonate, unsubstituted or substituted acetate, sulphate, hydrogen sulphate, nitrate, perchlorate, or oxalate