Tingyou Li

Potent in vivo antinociception and opioid receptor preference of the novel analogue [Dmt1]endomorphin-1.

[Dmt1]Endomorphin-1 is a novel analogue of the potent mu-opioid agonist endomorphin-1. Given the physiological role of endomorphin-1 in vivo, this compound was investigated to determine if the antinociception occurred through systemic, supraspinal or in a combination of both neuronal pathways. This compound exhibited a potent dose-dependent effect intracerebroventricularly in both spinal and supraspinal regions, and was blocked by opioid antagonist naloxone, which verified the involvement of opioid receptors. Specific opioid antagonists characterized the apparent receptor type: beta-funaltrexamine (mu1/mu2-irreversible antagonist) equally inhibited spinal- and central-mediated antinociception; on the other hand, naloxonazine (mu1-subtype) was ineffective in both neural pathways and naltrindole (delta-selective antagonist) partially (26%), though not significantly, blocked only the spinal-mediated antinociception. Therefore, spinal antinociception was primarily triggered by mu2-subtypes without involvement of mu1-opioid receptors; however, although a slight enhancement of antinociception by delta-receptors cannot be completely ruled out since functional bioactivity indicated mixed mu-agonism/delta-antagonism. In terms of the CNS action, [Dmt1]endomorphin-1 appears to act through mu2-opioid receptor subtypes.

[N-Allyl-Dmt1]-Endomorphins Are μ-Opioid Receptor Antagonists Lacking Inverse Agonist Properties

[N-Allyl-Dmt1]-endomorphin-1 and -2 ([N-allyl-Dmt1]-EM-1 and -2) are new selective μ-opioid receptor antagonists obtained by N-alkylation with an allyl group on the amino terminus of 2′,6′-dimethyl-l-tyrosine (Dmt) derivatives. To further characterize properties of these compounds, their intrinsic activities were assessed by functional guanosine 5′-O-(3-[35S]thiotriphosphate) binding assays and forskolin-stimulated cyclic AMP accumulation in cell membranes obtained from vehicle, morphine, and ethanol-treated SK-N-SH cells and brain membranes isolated from naive and morphine-dependent mice; their mode of action was compared with naloxone or naltrexone, which both are standard nonspecific opioid-receptor antagonists. [N-Allyl-Dmt1]-EM-1 and -2 were neutral antagonists under all of the experimental conditions examined, in contrast to naloxone and naltrexone, which behave as neutral antagonists only in membranes from vehicle-treated cells and mice but act as inverse agonists in membranes from morphine- and ethanol-treated cells as well as morphine-treated mice. Both endomorphin analogs inhibited the naloxone- and naltrexone-elicited withdrawal syndromes from acute morphine dependence in mice. This suggests their potential therapeutic application in the treatment of drug addiction and alcohol abuse without the adverse effects observed with inverse agonist alkaloid-derived compounds that produce severe withdrawal symptoms.

Synthesis of Opioidmimetics, 3-[H-Dmt-NH(CH2)m]-6-[H-Dmt-NH(CH2)n]-2(1H)-pyrazinones, and Studies on Structure-Activity Relationships

Opioidmimetics containing 3-[H-Dmt-NH-(CH(2))(m)]-6-[H-Dmt-NH-(CH(2))(n)]-2(1H)-pyrazinone symmetric (m = n, 1-4) (1 - 4) and asymmetric (m, n = 1 - 4) aliphatic chains (5 - 16) were synthesized using dipeptidyl chloromethylketone intermediates. They had high mu-affinity (K(i)mu = 0.021 - 2.94 nM), delta-affinity (K(i)delta = 1.06 - 152.6 nM), and mu selectivity (K(i)delta/K(i)mu = 14 - 3,126). The opioidmimetics (1 - 16) exhibited mu agonism in proportion to their mu-receptor affinity. delta-Agonism was essentially lacking in the compounds except (4) and (16), and (1) and (2) indicated weak delta antagonism (pA(2) = 6.47 and 6.56, respectively). The data verify that a specific length of aliphatic linker is required between the Dmt pharmacophore and the pyrazinone ring to produce unique mu-opioid receptor ligands.

Immediate deamination from the aminomethyl group attached to 1,2-dihydropyrazin-2-one derivative during catalytic hydrogenation

Abstract The catalytic hydrogenation of 3,6-bis(benzyloxycarbonylaminomethyl)-5-methyl-1,2-dihydropyrazin-2-one to remove benzyloxycarbonyl (Z) groups resulted in a side reaction. Purification by reverse-phase HPLC and analysis by proton nuclear magnetic resonance (1H NMR) spectroscopy identified the product as 3-aminomethyl-5,6-dimethyl-1,2-dihydropyrazin-2-one. It was determined through the synthesis of two 1,2-dihydropyrazin-2-one derivatives, composed of alanine and 2,3-diaminopropionic acid that deamination occurred specifically and easily (under atmospheric pressure and at the room temperature) only in the case of 6-benzyloxycarbonylaminomethyl-3,5-dimethyl-1,2-dihydropyrazin-2-one. The catalytic hydrogenation of 3,6-bis(benzyloxycarbonylaminomethyl)-5-methyl-1,2-dihydropyrazin-2-one specifically yields the deaminated product, 3-aminomethyl-5,6-dimethyl-1,2-dihydropyrazin-2-one.