An amphiphilic compound is provided capable of forming vesicles or liposomes, said amphiphilic compound having at least one headgroup containing a selectively cleavable group or moiety such as a residue of a choline or phenylalanine derivative, and at least one hydrogen-bonding group located either within said headgroup and/or in close proximity thereto. The cleavable group or moiety is cleaved under selective conditions including change of chemical, physical or biological environment and is preferably cleaved enzymatically in a biological environment such as the brain or the blood. Vesicles or liposomes made from said amphiphilic compounds are suitable for delivery of a therapeutic substance or a diagnostic agent specifically to a target organ or tissue, or for delivery of a nucleic acid for gene therapy.