Substance P analogs containing homoglutamine at position 5 and 6

Six substance P (SP) analogs, in which the glutaminyl residue(s) at the position(s) 5 or/and 6 were replaced by homoglutamine (Hgn), were prepared using a novel Nα,Nca–(Boc)2–Hgn–OH by the solid phase method. The activity of the analogs was assayed on isolated guinea pig organs. Results indicate that the elongation of the methylene on glutaminyl residue(s) in SP enhances the activity on isolated guinea pig ileum.