Novel urea derivatives having nitrogen aromatic heterocycle

A compound represented by the following general formula [I] or a salt thereof,

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• wherein R1 is hydrogen, lower alkyl, phenyl or a group of the following formula [II].
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• R2 is hydrogen, lower alkyl, cycloalkyl, phenyl, carboxyl or ester thereof, and can join with sulfur adjacent to A1 to form a nonaromatic heterocycle having sulfur in the ring.
• R3 and R4, being the same or different, are hydrogen, lower alkyl, lower alkenyl, cycloalkyl, cycloalkenyl or phenyl.
• R5 is hydrogen, lower alkyl, hydroxy or lower alkoxy.
• R6 is an aromatic heterocycle having nitrogen in the ring.
• A1 and A2, being the same or different, are lower alkylene.
• Each lower alkyl defined above can be substituted by cycloalkyl, cycloalkenyl, adamantyl, phenyl, halogen, hydroxy, lower alkoxy or an aromatic or nonaromatic heterocycle having nitrogen in the ring.
• Each phenyl defined above can be substituted by lower alkyl, phenyl, hydroxy, lower alkoxy, halogeno-lower alkoxy, halogen, nitro, carboxyl or ester thereof.
• The aromatic or nonaromatic heterocycle having nitrogen in the ring defined above can be substituted by lower alkyl, halogeno-lower alkyl, hydroxy-lower alkyl, cycloalkyl, phenyl, halogen, hydroxy or lower alkoxy.