Structural studies on some tamoxifen derivatives.

Abstract

The crystal structures of four derivatives of the antiestrogenic drug tamoxifen are described. These are of 2-hydroxy-, 3-hydroxy-, and 2-methyl-4-hydroxytamoxifen and of 1-(4-methoxyphenyl)-2-phenyl-1-[(tetrahydropyran-2-yloxy)phenyl]-1 -butanol, the synthetic precursor to 2-hydroxytamoxifen. All compounds have trans stereochemistry about the ethylene double bond, as in tamoxifen itself. The orientations of the hydroxy substituents have been found to differ by 180 degrees, depending on the nature of the compound. Empirical energy calculations have been used to show that the barrier to free rotation for the hydroxy-substituted phenyl rings is too high for interconversion to take place. These orientational differences are, it is suggested, related to the marked differences in estrogen receptor binding ability.