We evaluated antitrichomonal effects of δ opioid receptor (DOR) agonists and antagonists. Although all the agonists were inactive, the DOR antagonists BNTX (2a) and its derivatives 2b-d showed antitrichomonal activity with MIC of 20-40 μM. In addition, the development of a more effective synthetic method for the BNTX derivatives was achieved by using the Knoevenagel condensation.