New scaffolds in the development of mu opioid-receptor ligands

Novel Dimethyltyrosine-Tetrahydroisoquinoline Peptidomimetics with Aromatic Tetrahydroisoquinoline Substitutions Show in Vitro Kappa and Mu Opioid Receptor Agonism

The dimethyltyrosine-tetrahydroisoquinoline (Dmt-Tiq) scaffold was originally developed in the production of selective delta opioid receptor (DOR) antagonists. Installation of a 7-benzyl pendant on the tetrahydroisoquinoline core of this classic opioid scaffold introduced kappa opioid receptor (KOR) agonism. Further modification of this pendant resulted in retention of KOR agonism and the addition of mu opioid receptor (MOR) partial agonism, a bifunctional profile with potential to be used in the treatment of cocaine addiction.

Effect of lysine at C-terminus of the Dmt-Tic opioid pharmacophore

Substitution of Gly with side-chain-protected or unprotected Lys in lead compounds containing the opioid pharmacophore Dmt-Tic [H-Dmt-Tic-Gly-NH-CH(2)-Ph, mu agonist/delta antagonist; H-Dmt-Tic-Gly-NH-Ph, mu agonist/delta agonist; and H-Dmt-Tic-NH-CH(2)-Bid, delta agonist (Bid = 1H-benzimidazole-2-yl)] yielded a new series of compounds endowed with distinct pharmacological activities. Compounds (1-10) included high delta- (Ki(delta) = 0.068-0.64 nM) and mu-opioid affinities (Ki(mu) = 0.13-5.50 nM), with a bioactivity that ranged from mu-opioid agonism {10, H-Dmt-Tic-NH-CH[(CH2)4-NH2]-Bid (IC50 GPI = 39.7 nM)} to a selective mu-opioid antagonist [3, H-Dmt-Tic-Lys-NH-CH2-Ph (pA2(mu) = 7.96)] and a selective delta-opioid antagonist [5, H-Dmt-Tic-Lys(Ac)-NH-Ph (pA2(delta) = 12.0)]. The presence of a Lys linker provides new lead compounds in the formation of opioid peptidomimetics containing the Dmt-Tic pharmacophore with distinct agonist and/or antagonist properties.

New 2',6'-dimethyl-L-tyrosine (Dmt) opioid peptidomimetics based on the Aba-Gly scaffold. Development of unique mu-opioid receptor ligands

The Aba-Gly scaffold, incorporated into Dmt-Tic ligands (H-Dmt-Tic-Gly-NH-CH2-Ph, H-Dmt-Tic-Gly-NH-Ph, H-Dmt-Tic-NH-CH2-Bid), exhibited mixed micro/delta or delta opioid receptor activities with micro agonism. Substitution of Tic by Aba-Gly coupled to -NH-CH2-Ph (1), -NH-Ph (2), or -Bid (Bid=1H-benzimidazole-2-yl) (3) shifted affinity (Ki(micro)=0.46, 1.48, and 19.9 nM, respectively), selectivity, and bioactivity to micro-opioid receptors. These compounds represent templates for a new class of lead opioid agonists that are easily synthesized and suitable for therapeutic pain relief.

Antinociceptive activity of new imidazolidine carbonyl derivatives

Synthesis and pharmacological activity of 8-aryl-3,4-dioxo-2H,8H-6,7-dihydroimidazo[2,1-c] [1,2,4]triazines (A) are presented. The title compounds were obtained from 1-aryl-2-hydrazinoimidazolines (1) by cyclization reaction with ethyl oxalate (2). They were tested for pharmacological activity in behavioral animal tests (A1, A3, A5, A6, A8, A9). With relatively low acute toxicity (LD50 in range from 1100 to over 2000 mg kg(-1), intraperitoneally, i.p.), some of them exhibited significant antinociceptive activity as the result of the 'writhing' test indicated. Especially strong antinociception for compound A8 and significant for A6 was observed in doses of 12.5-200 mg (0.00625-0.1 LD50) and 37.5-150 mg (0.025-0.1 LD50), respectively. Reversion of the antinociception for A1 and A8 produced in the 'writhing' test by 5 mg kg(-1) dose of naloxon can suggest an opioid-like mechanism of their analgesic activity. Additionally, compound A9 reduced number of the "head twitch" episodes after 5-hydroxytryptophan (5-HTP) administration with no antinociceptive effect at all and compound A3 showed significant protection in the pentylentetrazol-induced seizure model. Differences observed in the activity spectrum between A8 and A9 derivatives can be explained on the base of difference in the amido-imido tautomeric equilibrium observed between these two compounds.