The present invention relates to certain compounds of formula (I) below or a pharmaceutically acceptable salt or solvate thereof: nwherein, R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 and R 8 are as defined in the specification; to a process for preparing such compounds; to a pharmaceutical composition comprising such compounds and to the use of such compounds in medicine.