Given an abstract from a research paper, your task is to identify and label relationships between chemical compounds and genes mentioned in the abstract.

The relationship type must be one of ['DOWNREGULATOR', 'SUBSTRATE', 'INDIRECT-REGULATOR', 'PART-OF', 'MODULATOR-ACTIVATOR', 'REGULATOR', 'INHIBITOR', 'COFACTOR', 'UPREGULATOR', 'ACTIVATOR', 'ANTAGONIST', 'NOT', 'INDIRECT-DOWNREGULATOR', 'SUBSTRATE_PRODUCT-OF', 'INDIRECT-UPREGULATOR', 'AGONIST', 'PRODUCT-OF', 'MODULATOR', 'DIRECT-REGULATOR', 'UNDEFINED', 'AGONIST-INHIBITOR', 'AGONIST-ACTIVATOR', 'MODULATOR-INHIBITOR'].

Please format your output as a JSON array. Each entry in the array should express a single relation, formatted as ["<Entity_A>", "<RELATION_A_B>", "<Entity_B>"]. If no relations can be found, please output an empty JSON array [].

Abstract:

Design, Synthesis, and Pharmacological Characterization of Novel Endomorphin-1 Analogues as Extremely Potent μ-Opioid Agonists. Recently we reported the synthesis and structure-activity study of endomorphin-1 (EM-1) analogues containing novel, unnatural α-methylene-β-aminopropanoic acids (Map). In the present study, we describe new EM-1 analogues containing Dmt (1), (R/S) -βPro (2), and (ph) Map (4) / (2-furyl) Map (4). All of the analogues showed a high affinity for the μ-opioid receptor (MOR) and increased stability in mouse brain homogenates. Of the new compounds, Dmt (1) - (R) -βPro (2) -Trp (3) - (2-furyl) Map (4) (analogue 12) displayed the highest affinity toward MOR, in the picomolar range (Ki (μ) = 3.72 pM). Forskolin-induced cAMP accumulation assays indicated that this analogue displayed an extremely high agonistic potency, in the subpicomolar range (EC50 = 0.0421 pM, Emax = 99.5%). This compound also displayed stronger in vivo antinociceptive activity after iv administration when compared to morphine in the tail-flick test, which indicates that this analogue was able to cross the blood-brain barrier.
[["Endomorphin-1", "AGONIST", "\u03bc-Opioid"]]