Increased Hydrophobicity and Estrogenic Activity of Simple Phenols with Silicon and Germanium-Containing Substituents

Here, we report the systematic synthesis and characterization of simple phenols bearing a trialkyl(aryl)silyl or trialkyl(aryl)germyl functional group as a hydrophobic substituent. These silicon and germanium analogues exhibited higher hydrophobicity than the corresponding carbon analogues, with a difference in log P value of approximately 0.6, independent of the alkyl(aryl) species. Trimethylsilylphenol and trimethylgermylphenol exhibited smaller pK(a) values than the corresponding carbon analogue or unsubstituted phenol, indicating that trialkylsilyl and trialkylgermyl functional groups have a negative substituent constant (sigma). The trialkylsilyl- and trialkylgermylphenols exhibited more potent estrogenic activity as compared with the carbon analogues. The substituent parameters and structure-activity relationship reported here may be helpful for drug discovery utilizing the heavier group 14 elements.