There are provided according to the invention compounds of the formula (I) or a salt or solvate thereof, wherein: n represents an integer 1 to 6; N represents an integer 1 to 15; R
1
represents (CO)
x
C
1-9
alkyl or (CO)
x
C
1-9
fluoroalkyl, which fluoroalkyl moiety contains at least 1 fluorine atom and not more than 3 consecutive perfluorocarbon atoms wherein x represents 0 or 1; and R
2
and R
3
independently represent C
1-3
alkyl or hydrogen. There are also provided pharmaceutical aerosol formulations employing said compounds as suspension stabilising agents.