Compounds of formula (I): or salts or solvate thereof, wherein: n and N independently represent an integer 2 to 12; m1 and m2 independently represent an integer 1 to 15; and R1 and R2 independently represent —(CO)xC1-9 alkyl or —(CO)xC1-9 fluoroalkyl, which fluoroalkyl moiety contains at least 1 fluorine atom and not more than 3 consecutive perfluorocarbon atoms wherein x represents 0 or 1, as well as pharmaceutical formulations containing such compounds and processes for the manufacture of such compounds are disclosed. Intermediates of such compounds and processes for the manufacture of such intermediates are also disclosed.