| abstract |
A compound of formula (I) or a pharmaceutically acceptable salt thereof, or a pharmaceutically acceptable solvate thereof, wherein R?1 and R2¿ may each represent hydrogen or C¿1-6?alkyl, providing that at least one of R?1 or R2¿ represents C¿1-6?alkyl; and R?3 and R4¿ each represent hydrogen or R3 together with R4 represents a bond; a process for the preparation of such a compound, a pharmaceutical composition comprising such a compound, and the use of such a composition and compound in medicine. |