Patent ID: 7288565

Claim:
A compound represented by the following formula (Ia) or a salt thereof: wherein R 1 represents a hydrogen atom, a C 1-10 alkyl group optionally having a substituent, or a protecting group of N; R 2 represents a C 1-10 alkyl group optionally having a substituent or a C 2-10 alkenyl group optionally having a substituent; R 3 and R 4 independently represent a hydrogen atom or a protecting group of hydroxyl group; X represents —N(R 5 )R 6 or a residue of amino acid or of an amino group of a peptide wherein R 5 and R 6 independently represent a hydrogen atom, a C 1-10 alkyl group optionally having a substituent, or a C 3-12 cycloalkyl group optionally having a substituent; and Y represents a hydrogen atom, —CH 2 NH 2 , —CONH 2 , or —COOH.