“…60 As shown in Table 4, the difluoro indoles 28a and 28c were potent M 1 PAMs on both human (EC 50 = 210 nM and EC 50 = 224 nM, respectively) and rat (EC 50 = 141 nM and EC 50 = 191 nM, respectively) receptors with comparable efficacies (86–92% ACh Max) and rat CNS penetration ( K p ’s = 0.11, K p,uu ’s = 0.02); however, they were both 5- to 14-fold less potent than 16 (hEC 50 = 31 nM, rEC 50 = 30 nM), 31 (hEC 50 = 59 nM, rEC 50 = 39 nM), 32 (hEC 50 = 48 nM, rEC 50 = 24 nM), and 33 (hEC 50 = 17 nM, rEC 50 = 18 nM) but with similar efficacies and K p ’s/ K p,uu ’s. Thus, absolute M 1 PAM potency was a differentiating point; however, 31 was similarly potent to the M 1 ago-PAMs ( 16 , 32 , and 33 ) that induced seizures.…”