| abstract |
Compounds of the formula I ** Formula ** in which R1 to R3 respectively mean, independently of each other, H, hydroxy or alkoxy with 1 to 8 carbon atoms, R4 means alkyl with 1 to 4 carbon atoms, H , hydroxy or alkoxy with 1 to 8 carbon atoms, R5 means H or hydroxy and R6 means H or alkyl with 1 to 18 carbon atoms or their salts, without, however, all residues R1 to R4 together can be equal to H. |