| abstract |
A compound selected from the compounds of formula (V): and pharmaceutically acceptable salts, hydrates and solvates thereof, wherein: R1 is methyl, ethyl, n-propyl, isopropyl, n-butyl or, isobutyl, sec-butyl , tert-butyl, n-pentyl, isopentyl, sec-pentyl, neopentyl, 1,1-diethoxyethyl, phenyl, cyclohexyl, 2-pyridyl, 3-pyridyl or 4-pyridyl; R2 is hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, phenyl or cyclohexyl; R3 is hydrogen; and R4 is hydrogen. |