The direct inhibition of estrogen synthesis targeting aromatase inhibition is considered to be an effective strategy towards breast cancer treatment (Altundag and Ibrahim, 2006; Brueggemeier et al., 2005; Favia et al., 2013). The majority of available non-steroidal aromatase inhibitors exhibit their competitive inhibitory activity through the coordination of the nitrogen (N) atom presented in the molecule with the iron heme atom of the enzyme (Recanatini et al., 2002). Currently, aza-based aromatase inhibitors, i.e., letrozole and anastrozole, have been approved by the FDA as standard drugs for breast cancer treatment. In addition, natural products, i.e., flavonoids (Kao et al., 1998; Karjalainen et al., 2000; Le Bail et al., 2001) and sesquiterpene lactones (Blanco et al., 1997, 2001), whose carbonyl oxygen (O) atoms have been noted to play a role in heme coordination (Kao et al., 1998).