[Problems to be Solved]
To provide a novel compound having antiviral activity, especially inhibitory activity against HIV integrase, a pharmaceutical composition, especially anti-HIV drug, containing the same.
[Means to Solve the Problem]
A compound of the formula:

(wherein:
R 1 is optionally substituted aralkyl;
R 2 and R 3 are each independently hydrogen, optionally substituted alkyl, optionally substituted amino, optionally substituted alkenyl or optionally substituted alkoxy (provided that each substituent for "optionally substituted" is a noncyclic group);
R 4 is hydrogen, optionally substituted carboxy, optionally substituted formylamino, optionally substituted carbamoyl, optionally substituted amino (provided that a substituent on amino in "optionally substituted formylamino", "optionally substituted carbamoyl" and "optionally substituted amino" may form an optionally-substituted N-atom containing heterocyclic ring together with an adjacent N atom), optionally substituted alkyl, optionally substituted alkenyl, optionally substituted aryl, or optionally substituted heteroaryl) or a salt thereof.