Cationic lipids for gene therapy

A compound of Formula I

• R.sub.1 R.sub.2 N--C(O)--A--X Formula I
• wherein:
• R.sub.1 and R.sub.2, which may be the same or different, are C.sub.10 -C.sub.26 hydrocarbyl groups;
• A is a alkylene group wherein one or more methylene groups is optionally replaced by a group Y (provided that none of the Y groups are adjacent to each other), where each Y is independently in the direction shown, --O--, --OC(O)--, --C(O)O--, --NR.sub.5 --, --NR.sub.5 C(O)--, --C(O)NR.sub.5 --, NR.sub.5 C(O)NR.sub.5 --, --NR.sub.5 C(O)O--, --OC(O)NR.sub.5 --, --S(O).sub.n -- (where n is 0, 1 or 2) or --NZ--C(.dbd.NZ)NZ--, wherein each Z is independently H or --(CH.sub.2).sub.m NR.sub.5 --C(.dbd.NR.sub.5)NR.sub.5 with m being an integer from 1-10, and each R.sub.5 is independently H or lower alkyl;
• X is:
• a --NH--C(.dbd.NR.sub.3)NHR.sub.4, wherein R.sub.3 and R.sub.4 are independently hydrocarbyl, haloalkyl, hydroxyalkyl, O-protected hydroxyalkyl, alkoxyalkyl, haloalkoxyalkyl, aryloxyalkyl, aminoalkyl, mono- or di-substituted aminoalkyl, N-protected-aminoalkyl, acyl, alkoxycarbonyl, aryloxycarbonyl, --C(O)NR.sub.6 R.sub.7 (where R.sub.6 and R.sub.7 are independently H or hydrocarbyl) or a nitrogen protecting group;
• provided that:
• when R.sub.1 and R.sub.2 are both identical C.sub.16 alkyl groups, A is not a butylene chain;
• and salts, solvates, resolved and unresolved enantiomers, diastereomers and mixtures thereof.