Abstract: The present invention relates to a compound represented by Formula [I] or a pharmaceutically acceptable salt or ester thereof: wherein: X1, X2, X3, and X4, which may be identical or different, are each C or N, provided that none to two of X1, X2, X3, and X4 is/are N; Y is CH or N; R1, R1?, R2, R2?, R3, R3?, R4, and R4?, which may be identical or different, are each a hydrogen atom, a lower alkyl group, or the like; R5 is a hydrogen atom or a methyl group; R6 and R7, which may be identical or different, are each a hydrogen atom, a lower alkyl group, or the like; R8 and R8?, which may be identical or different, are each a hydrogen atom, a lower alkyl group, or the like; R9 is an aryl group or a heteroaryl group which may be substituted; and n is an integer from 1 to 3, and a PLK1 inhibitor or an anticancer agent containing the same.

Abstract: The invention relates to compounds of a general formula (I): wherein Ar1 is an optionally-substituted aryl or heteroaromatic group; R1 is an optionally-substituted lower alkyl, lower alkenyl, lower alkynyl or cyclo-lower alkyl group, or is an aryl, aralkyl or heteroaromatic group optionally having a substituent; R2 is a hydrogen atom, a lower alkyl group, a lower alkenyl group or a lower alkynyl group, or is an aryl, aralkyl or heteroaromatic group optionally having a substituent; R3 is a hydrogen atom or a lower alkyl group; R4 is a hydrogen atom, a halogen atom, a hydroxyl group, a lower alkyl group or a group of —N(R1k)R1m; T and U are a nitrogen atom or a methine group, etc. The compounds of the invention have excellent Weel kinase-inhibitory effect and are therefore useful in the field of medicines, especially treatment of various cancers.