Ester derivatives of the mammary-tumor-inhibiting antiestrogen 2,3-bis(2-fluoro-4-hydroxyphenyl)-2,3-dimethylbutane.

The synthesis of the bisacetate (8), the bisdichloroacetate (9), the biscarbamate (10) and the bisphosphate (11) of the "partial" antiestrogen 2,3-bis(2-fluoro-4-hydroxyphenyl)-2,3-dimethylbutane (7) is described. In the case of 8-10 the introduction of ester functions slightly reduces the estrogen receptor affinity of 7. However, it was strongly diminished in 11. Compared with 7 the estrogenic potency of 8-11 is moderately increased. Compounds 8-11 cause a strong inhibition of the hormone-dependent MXT M3.2 mouse mammary tumor. Only 9 containing cytotoxic dichloroacetate groups shows a significantly better antitumor effect than 7.