Aromatase inhibitors (AIs) are disclosed which are useful in the treatment and prevention of post-menopausal breast cancer. New AIs derived from natural products are disclosed that are evaluated for clinical utility for treating post-menopausal breast cancer and may also act as chemopreventive agents for preventing breast cancer. Several pure compounds demonstrated AI activity using a noncellular, enzyme-based microsomal and a cell-based aromatase assay. Correlations are made between structural classes with levels of aromatase inhibition. The disclosure may be utilized to direct synthetic modification of natural product scaffolds to enhance aromatase inhibition or to standardize botanical dietary supplements for increased aromatase inhibition activity.