Quantitative structure-activity relationships among steroids. Investigations of the use of steric parameters.

The importance of steric factors in quantitative structure-activity relationships involving steroid hormones is discussed. a variety of steric parameters, such as parachlor, molecular volume, van der Waals volume, and including difference and squared steric terms, is explored in an attempt to find preferred forms for such expressions. Improved correlations for 6-substituted 16-methylene-17alpha-acetoxy-4,6-pregnadiene-3,20-dione derivatives were found in which activity is related to pi and a squared or difference steric factor. The activity of 9alpha-substituted cortisols correlates well with sigma I and a simple steric factor, provided that the 9alpha-hydroxylated compound is excluded from the series.