TRICYCLIC CYTOPROTECTIVE COMPOUNDS

Compounds of formula (I): [in which: X is a group of formula >CR1R2 or >SO2; Y is a group of formula >NH or >CR1R2; Z is a group of formula >C-O or >CH2 or a direct bond; R1 is hydrogen and R2 is hydrogen, carboxy or hydroxy; or R1 and R2 together represent an oxo group, a methylenedioxy group or a hydroxyimino group; R3 is hydrogen or lower alkyl; R4 represents two hydrogen atoms, or an oxo or hydroxyimino group; R5 is hydrogen, lower alkyl or halogen; R6 is hydrogen, lower alkoxy or carboxy; R7 and R8 are each hydrogen, lower alkyl or halogen; and pharmaceutically acceptable salts and esters thereof can be used for the treatment or prophylaxis of acute or chronic neurodegenerative diseases or conditions such as Alzheimer's Disease, Parkinson's Disease, Huntington's Chorea, Multiple Sclerosis or the sequelae to acute ischaemic events such as heart attack, stroke or head injury and for protection against ischaemic damage to tissues of peripheral organs.