Patent ID: 7074823

Claim:
A compound represented by general formula (IA) or a salt thereof: wherein R 1 and R 2 independently represent a hydrogen atom or a group represented by formula (A): wherein X 1 , X 2 , X 3 , and X 4 independently represent a hydrogen atom, an alkyl group, a 2-pyridylmethyl group, or a protective group for an amino group, and m and n independently represent 0 or 1 and at least one of m and n is 1, provided that R 1 and R 2 do not simultaneously represent hydrogen atoms; R 3 and R 4 independently represent a hydrogen atom or a halogen atom; and R 5 and R 6 independently represent a hydrogen atom, an alkylcarbonyl group, or an alkylcarbonyloxymethyl group.