... Bioorganic & Medicinal Chemistry Letters. Volume 17, Issue 2, 15 January 2007, Pages 439–443. ... Any modification on R 1 , R 2 , R 3 , R 4 , and R 5 seemed to be detrimental to the activity and led to inactive compounds, as exemplified by 10a–b, 10e–g, and 10i–k in Table 1. Compound 10h with trifluoro acetyl substitution on R 6 was an exception that maintained agonistic activity on levator ani muscle and prostate. ... 10f, CN, CF 3, H, Me, per-F–Ph, H, 21, <10, <10. ...