PURPOSE: To obtain a new amino acid easily obtainable from L-lysine, belonging to a nonnatural-type amino acid having photo DNA-cleaving activity which is specific in terms of base sequence, and accordingly having photosensitizing activity.

CONSTITUTION: This is a new amino acid expressed by formula I (R1 and R2 are each H or NO2 but R1 and R2 can not be NO2 at the same time) and having photosensitizing activity, e.g. N-(5-amino-5methoxycarbonylpentyl)-1,8- naphthalimide of formula II. A compound of formula I, e.g. a compound of formula II is obtained by reacting Boc-L-Lys-OMe with 1,8-naphthalic anhydride. This new amino acid is synthesized from L-lysine by a single step reaction on a large scale. Further, the amino acid strongly binds to DNA and cleaves DNA and RNA specifically in terms of base sequence by photoirradiation at 300-380nm. Base character of DNA cleavage is modified by changing a substituent at naphthalimide position.