Interleukin 17(A) is a pro-inflammatory cytokine involved in several auto-immune and inflammatory diseases. Current antagonists against IL17(A) or its receptor (IL17R) that show efficacy in clinical trials are monoclonal-antibodies (mAbs). However, recently designed artificial macrocyles are potent IL17-IL17R antagonists. Based on Co-crystal structures, a better understanding the biological activity and SAR of the macrocycles has been elucidated, demonstrating that macrocycles can compete with mAbs for difficult targets such as PPIs.