There are provided compounds of the formulawherein X, Y, R1, R2, R3,R3, R4, R5, R6and R7are as described herein and enantiomers and pharmaceutically acceptable salts and esters thereof. The compounds are useful as anticancer agents.本發明提供下式化合物其中X、Y、R1、R2、R3、R4、R5、R6及R7如本文中所述,以及其對映異構物及藥學上可接受之鹽與酯。此等化合物可用作抗癌劑。