Design and synthesis of KNT-127, a δ-opioid receptor agonist effective by systemic administration

We have reported previously the novel delta-opioid agonist, SN-28, which was more potent in in vitro assays than the prototype delta-agonists, TAN-67 and SNC-80. However, when administered by subcutaneous injection, this compound showed no analgesic effect at dosages greater than 30 mg/kg in the acetic acid writhing test. We speculated that SN-28 was not effective in the test because the presence of the charged ammonium groups prevented its penetration through the blood-brain barrier. On the basis of our proposal, we designed the novel delta-agonist, KNT-127, which was effective with systemic administration. (C) 2010 Elsevier Ltd. All rights reserved.