COMPOUND CAPABLE OF INTRACEREBRAL RESIDENCE AND USE THEREOF

A group of novel compounds which can pass through the blood-brain barrier (BBB) with a drug carried thereon and reside in the brain to release the drug and a group of known compounds having the above characteristics. More specifically, a compound represented by general formula (Ia) and a salt thereof, wherein R represents hydroxy, carboxy, amino which may be substituted by C1-C6 alkyl, or C1-C6 alkyl which may be substituted by a 5-to 7-membered saturated heterocyclic group, R represents hydrogen or C1-C6 alkyl, R represents hydrogen or C1-C6 alkyl which may be hydroxylated, R represents hydrogen or C1-C6 alkyl, R represents amino acid residue, or -S-R or -CO-R (wherein R represents C1-C14 alkyl which may be substituted by a 5- to 7-membered saturated heterocyclic group, C1-C14 alkyl, C2-C6 alkenyl, aryl or a 5- to 7-membered saturated ring group), or a group represented by general formula (IVa), wherein R , R , R and R are each as defined above, and symbol ... represents either a single or a double bond, provided that at least one of R , R and R represents hydroxy, carboxy or amino.