Synthesis of optically active TAN-67, a highly selective delta opioid receptor agonist, and investigation of its pharmacological properties.

We have synthesized the nonpeptidic highly selective delta opioid receptor agonist, (+/-)-TAN-67, (4aS*, 12aR*)-4a-(3-hydroxyphenyl)-2-methyl-1,2,3,4,4a,5,12,12a-octahydropyrido [3,4-b] acridine. In spite of high potent agonist activity for the delta opioid receptor in in vitro assay, (+/-)-TAN-67 afforded no analgesic activity in the mouse warm-plate test. This result led us to separate (+/-)-TAN-67 into optically pure compounds. Each enantiomer of racemic TAN-67 was synthesized from the corresponding optically active 6-oxodecahydroisoquinoline which was obtained by fractional recrystallization of its optically pure di-p-toluoyl tartaric acid salt. In bioassay using mouse vas deferens, (-)-TAN-67 showed full agonist activity (IC50 = 3.65 nM). On the other hand, (+)-TAN-67 showed almost no agonist activity, but interestingly afforded hyperalgesic activity in vivo (i.t. injection).

Rational drug design and synthesis of a highly selective nonpeptide delta-opioid agonist, (4aS*,12aR*)-4a-(3-hydroxyphenyl)-2-methyl- 1,2,3,4,4a,5,12,12a-octahydropyrido[3,4-b]acridine (TAN-67).

We designed highly selective non-peptide agonists for the delta-opioid receptor. On the basis of the "message-address" concept in this field and the accessory site hypothesis, a novel class of heterocycle-fused octahydroisoquinoline derivatives were synthesized. One of these compounds [(4aS*,12aR*)-4a-(3-hydroxyphenyl)-2-methyl-1,2,3,4,4a,5,12, 12a -octahydropyrido[3,4-b]acridine, TAN-67 (2)] showed high selectivity for the delta-opioid receptor (Ki = 1.12 nM) in guinea-pig cerebrum with a 2070-fold lower affinity for the mu-opioid receptor and a 1600-fold lower affinity for the kappa-opioid receptor. TAN-67 was a potent delta-opioid receptor agonist with an IC50 value of 6.61 nM in the mouse vas deferens assay that was reversed by naltrindole (NTI) (Ke = 0.21). Moreover, TAN-67 was shown to have antinociceptive activity following subcutaneous administration in the mouse acetic acid abdominal constriction assay that was antagonized by NTI (delta 1- and delta 2-antagonist) and 7-benzylidinenaltrexone (delta 1-antagonist), but not by naltriben (delta 2-antagonist). This systemically applicable non-peptide agonist will be useful for elucidating the pharmacological properties of the delta-opioid receptor.

Supraspinal delta 1-opioid receptor-mediated antinociceptive properties of (-)-TAN-67 in diabetic mice.

The antinociceptive potencies of the enantiomorphs of TAN-67 (2-methyl-4-alpha alpha-(3-hydroxyphenyl)-1,2,3,4,4 a 5, 12, 12 a alpha-octahydroquinolino[2,3,3,-g]isoquinoline), (-)-TAN-67 and (+)-TAN-67, given intracerebroventricularly (i.c.v.) on the antinociceptive response were studied in streptozotocin-induced diabetic mice using the tail-flick test. (-)-TAN-67 at doses of 3-10 micrograms given i.c.v. produced dose-dependent inhibition of the tail-flick response in both non-diabetic and diabetic mice. The antinociceptive effect of (-)-TAN-67 in the tail-flick test in diabetic mice was greater than that in non-diabetic mice. The antinociceptive effect of (-)-TAN-67 was not antagonized by pretreatment with either beta-funaltrexamine, a selective mu-opioid receptor antagonist, or nor-binaltorphimine, a selective kappa-opioid receptor antagonist. When 7-benzylidenenaltrexone, a selective delta 1-opioid receptor antagonist, was administered 10 min before treatment with (-)-TAN-67, the antinociceptive effect of (-)-TAN-67 was significantly antagonized. However, naltriben, a selective delta 2-opioid receptor antagonist, had no significant effect on the antinociceptive effect of (-)-TAN-67. On the other hand, in the tail-flick test. (+)-TAN-67 at doses of 3-30 micrograms given i.c.v. did not produce dose-dependent inhibition of the tail-flick response in either non-diabetic or diabetic mice. In conclusion, (-)-TAN-67, but not its enantiomer (+)-TAN-67, produced an antinociceptive effect through the activation of delta 1-opioid receptors.

Delta-1 opioid receptor-mediated antinociceptive properties of a nonpeptidic delta opioid receptor agonist, (-)TAN-67, in the mouse spinal cord.

The effects of enantiomorphs of TAN-67 (2-methyl-4a alpha-(3-hydroxyphenyl)-1,2,3,4,4a,5,12,12a alpha-octahydro-quinolino[2,3,3-g]isoquinoline), (-)TAN-67 and (+)TAN-67, given intrathecally (i.t.) on antinociceptive response with the tail-flick test were studied in male ICR mice. (-)TAN-67 at doses from 17.9 to 89.4 nmol given i.t. produced a dose- and time-dependent inhibition of the tail-flick response, whereas its enantiomer (+)TAN-67 even at smaller doses (1.8, 4.5 and 8.9 nmol) given i.t. decreased the latencies of the tail-flick response. In addition, (+)TAN-67 at higher doses (17.9-89.4 nmol) given i.t. produced scratching and biting pain-like responses. The antinociceptive response induced by i.t.-administered (-)TAN-67 was mediated by the stimulation of delta-1 but not by delta-2, mu or kappa opioid receptors, because the effect was blocked by the i.t. pretreatment with BNTX, but not by naltriben, [D-Phe-Cys-Tyr-[D-Try-Orn-Thr-Pen-Thr-NH2 or nor-binaltorphimine dihydrochloride. Pretreatment with (-)TAN-67 given i.t. 3 hr earlier attenuated the tail-flick inhibition induced by subsequent i.t. administration of (-)TAN-67 and by [D-Pen2,5]enkephalin (DPDPE). However, the tail-flick inhibition induced by [D-Ala2]deltorphin II, [D-Ala2,NMePhe4,Gly5-ol]enkephalin and U50,488H were not affected by (-)TAN-67 pretreatment. Conversely, pretreatment with DPDPE given i.t. 3 hr earlier attenuated the tail-flick inhibition induced by subsequent i.t. administration of (-)TAN-67 and by DPDPE. However, the tail-flick inhibition induced by [D-Ala2]deltorphin II was not affected by i.t. DPDPE pretreatment. It is concluded that (-)TAN-67 given i.t. produces delta-1 opioid receptor-mediated antinociception; on the other hand, its enantiomer (+)TAN-67 produces hyperalgesia. Present studies provide other evidence that delta-1 opioid receptors exist separated from delta-2 opioid receptor.