There are provided compounds of the formula wherein X, Y, Z, R1, R2, R3 and R4 are as described herein, and enantiomers and pharmaceutically acceptable salts and esters thereof; as well as methods for making such compounds, pharmaceutical compositions comprising said compounds, and their use in the treatment of cancer.本發明提供下式之化合物,其中X、Y、Z、R1、R2、R3及R4係如本文所述,及其對映異構體以及醫藥上可接受之鹽及酯;以及製備該等化合物之方法,包含該等化合物之醫藥組合物,及其治療癌症之用途。