A compound according to formula: or a reduced form thereof, or a pharmaceutically acceptable salt thereof, wherein R 1 and R 2 are each independently a hydrogen atom, an optionally substituted C 1-6 alkyl group, an optionally substituted C 2-6 alkenyl group, or an optionally substituted C 2-6 alkynyl group, an optionally substituted C 3-10 alicyclic hydrocarbon group, wherein the group may contain one or more unsaturated bonds, an optionally substituted, 3 to 8-membered heterocyclic group, wherein the group may contain one or more unsaturated bonds, and a carbon atom on the ring of the group is bonded with the nitrogen atom to which R 1 and R 2 are attached, an optionally substituted C 6-10 aryl group, or an optionally substituted, 5 to 12-membered monocyclic or polycyclic heteroaryl group, with the proviso that in the group, a carbon atom on its ring is bonded with the nitrogen atom to which R 1 and R 2 are attached, or R 1 and R 2 may be taken together with the nitrogen atom to which they are attached to form an optionally substituted, 3 to 8-membered, nitrogen-containing heterocycle, wherein the heterocycle may contain one or more unsaturated bonds; and R 3 is an optionally substituted C 6-10 aryl group, or an optionally substituted, 5 to 12-membered monocyclic or polycyclic heteroaryl group, with the proviso that in the group, a carbon atom on its ring is bonded with the carbon atom to which R 3 is attached. R 1 and R 2 are each independently a hydrogen atom, an optionally substituted C 1-6 alkyl group, an optionally substituted C 2-6 alkenyl group, or an optionally substituted C 2-6 alkynyl group, an optionally substituted C 3-10 alicyclic hydrocarbon group, wherein the group may contain one or more unsaturated bonds, an optionally substituted, 3 to 8-membered heterocyclic group, wherein the group may contain one or more unsaturated bonds, and a carbon atom on the ring of the group is bonded with the nitrogen atom to which R 1 and R 2 are attached, an optionally substituted C 6-10 aryl group, or an optionally substituted, 5 to 12-membered monocyclic or polycyclic heteroaryl group, with the proviso that in the group, a carbon atom on its ring is bonded with the nitrogen atom to which R 1 and R 2 are attached, or R 1 and R 2 may be taken together with the nitrogen atom to which they are attached to form an optionally substituted, 3 to 8-membered, nitrogen-containing heterocycle, wherein the heterocycle may contain one or more unsaturated bonds; and a hydrogen atom, an optionally substituted C 1-6 alkyl group, an optionally substituted C 2-6 alkenyl group, or an optionally substituted C 2-6 alkynyl group, an optionally substituted C 3-10 alicyclic hydrocarbon group, wherein the group may contain one or more unsaturated bonds, an optionally substituted, 3 to 8-membered heterocyclic group, wherein the group may contain one or more unsaturated bonds, and a carbon atom on the ring of the group is bonded with the nitrogen atom to which R 1 and R 2 are attached, an optionally substituted C 6-10 aryl group, or an optionally substituted, 5 to 12-membered monocyclic or polycyclic heteroaryl group, with the proviso that in the group, a carbon atom on its ring is bonded with the nitrogen atom to which R 1 and R 2 are attached, or R 1 and R 2 may be taken together with the nitrogen atom to which they are attached to form an optionally substituted, 3 to 8-membered, nitrogen-containing heterocycle, wherein the heterocycle may contain one or more unsaturated bonds; and R 3 is an optionally substituted C 6-10 aryl group, or an optionally substituted, 5 to 12-membered monocyclic or polycyclic heteroaryl group, with the proviso that in the group, a carbon atom on its ring is bonded with the carbon atom to which R 3 is attached. an optionally substituted C 6-10 aryl group, or an optionally substituted, 5 to 12-membered monocyclic or polycyclic heteroaryl group, with the proviso that in the group, a carbon atom on its ring is bonded with the carbon atom to which R 3 is attached.