The disclosure relates to Compounds of Formula (1): and pharmaceutically acceptable salts thereof wherein Z1, Z2, Z3, Xa, Xb, Xc, Y, X2, and X4 are as defined herein, compositions comprising an effective amount of a Compound of Formula (1) or a pharmaceutically acceptable salt thereof, and methods to treat or prevent a condition, such as cancer which overexpresses Her-kinases, comprising administering to an patient in need thereof a therapeutically effective amount of a Compound of Formula (1) or a pharmaceutically acceptable salt thereof.