. . . . "wherein R1 is a hydrogen atom, a lower alkyl group, an aryl group, or a heterocyclic group, R2 and R3, each of which may be the same or different, are individually a hydrogen atom or a lower alkyl group, and R4 and R5, each of which may be the same or different, are individually a hydrogen atom, a lower alkyl group, an aryl group which may have a substituent, or a heterocyclic group which may have" .