Synthesis and biological evaluation of 14-alkoxymorphinans. 11. 3-Hydroxycyprodime and analogues: opioid antagonist profile in comparison to cyprodime

A series of 3-hydroxy-substituted analogues (3-7) of the mu selective opioid antagonist cyprodime has been synthesized in order to evaluate the role of a hydroxy group at C-3 concerning mu opioid antagonist selectivity. Compounds 3-7 were tested in bioassays (electrical stimulated mouse vas deferens preparation and myenteric-plexus longitudinal muscle preparation of the guinea pig ileum) and opioid receptor binding assays. Antagonism of mu receptor-mediated responses induced by the mu selective agonist DAMGO afforded equilibrium dissociation constants in the mouse vas deferens preparation (Ke values) for compounds 3-7 which agreed closely with their affinities as determined by opioid receptor binding assays (Ki values). At kappa and delta receptors differences were apparent. Although the compounds had high affinity for both kappa and delta receptors in opioid receptor binding, they were very poor at antagonizing agonist responses mediated by kappa and particularly delta agonists in the mouse vas deferens preparation. None of the compounds tested showed agonist potency in the mouse vas deferens preparation or the myenteric-plexus longitudinal muscle preparation of the guinea pig ileum.

[Interaction of S-(+)-ketamine with opiate receptors. Effects on EEG, evoked potentials and respiration in awake dogs]

To check for suspected opioid-receptor mediated hypnotic and antinociceptive effects of S(+)-ketamine, highly selective antagonists were used after the anaesthetic. METHODS. To determine the hypnotic effects of increasing doses of S(+)-ketamine (2-5-10-20 mg/kg given at 10-min intervals), EEG power spectra (delta, theta, alpha, beta) were derived (Lifescan), and antinociceptive potency was evaluated using the somatosensory evoked potential (SEP, Lifescan) in awake, trained dogs (n = 10). To check for an opioid-receptor-related interaction, an antagonist of the methoxymorphinane series (HS-275, 80 micrograms/kg i.v.) with higher selectivity than naloxone for the mu-receptor was given at the end. After washout the same animals were exposed to S(+)-ketamine. This time, however, the highly selective delta-antagonist naltrindole (160 micrograms/kg i.v.) was given. To show up any respiratory depression arterial blood gases were taken after each dose. RESULTS. S(+)-Ketamine induced a dose-related increase in power in the theta band (3-8 Hz), with a ceiling effect at 10 mg/kg. The changes were reversed by both antagonists. In the beta band (13-30 Hz) and in the delta domain, power decreased or increased, respectively, in a highly significant manner (P < 0.005) at 20 mg/kg. Both effects reversed after the antagonists with an overshoot in beta (+12% and +14%, respectively) and a decrease in delta (-45% and -62%, respectively) compared with control. S(+)-Ketamine induced a dose-dependent increase in peak latency and depression of the SEP amplitude by a maximum of over 50%. Latency changes were completely reversed only by HS-275. Amplitude height was only partly restored by both antagonists. A clinical relevant decrease in PaO2 and increase in PaCO2 increase were seen at 20 mg/kg. Hypoxia was reversed by both antagonists; hypercapnia was only partially reversed. CONCLUSION. The results confirm the suspicion that S(+)-ketamine induces an opioid theta- and delta-receptor-mediated deep hypnotic effect. Blockade of nociceptive impulses in afferent sensory nervous pathways suggests an efficient analgesic effect mediated partly by the opioid mu-receptor. Other mechanisms, such as an interaction with the NMDA receptor, have to be taken into consideration to account for the full antinociceptive effect. Respiratory depression may be of clinical importance when high dosages of S(+)-ketamine are given.

Highly potent novel opioid receptor agonist in the 14-alkoxymetopon series

The newly synthesized 14-alkoxymetopon derivatives, 14-methoxymetopon, 14-ethoxymetopon, 14-methoxy-5-methyl-morphinone, exhibit high affinity for the naloxone binding sites in rat brain. A substantial decrease in affinity was observed, in the presence of NaCl indicating a high degree of agonist activity. All three 14-alkoxymetopon derivatives displayed high affinity for [3H][D-Ala2,(Me)Phe4,Gly-ol5]enkephalin ([3H]DAMGO) binding sites, much less potency toward delta sites and were the least effective at kappa sites. Isolated tissue studies using the guinea pig ileum preparation confirmed their high agonist potency. Following administration the new compounds produced naloxone reversible antinociceptive effects and were 130-300 times more potent than morphine in the acetic acid induced abdominal constriction model in the mouse, and the hot plate and tail flick tests in the rat. The compounds also produced dose-dependent muscle rigidity, and potentiated barbiturate-induced narcosis. The in vivo apparent pA2 values for naloxone against 14-ethoxymetopon and morphine were similar in analgesia, suggesting an interaction with the same (mu) receptor site. The dependence liability of 14-alkoxymetopon derivatives in the withdrawal jumping test was less pronounced than that of morphine in either rats or mice, similar to tolerance to the their analgesic action. It is concluded that the 14-alkoxymetopon derivatives studied are selective and potent agonists at mu opioid receptors, with reduced dependence liability.

[Pharmacodynamic effects of S-(+)-ketamine on EEG, evoked potentials and respiration. A study in the awake dog]

Until recently, only the racemic mixture of ketamine has been used in anaesthesia. Little is known of the central nervous effects of the pharmacologically more potent S(+)-isomer. Information in regard to the putative receptor site involved in the mediation of its anaesthetic/analgesic effect is particularly sparse. METHODS. In order to evaluate the anaesthetic and antinociceptive properties of S(+)-ketamine, a dose-response relationship of the compound on the EEG, somatosensory-evoked potentials (SEP), and respiration was established. Increasing doses (2, 5, 10, 20 mg/kg) were given to trained and awake dogs (n = 10) at 10-min intervals. In order to detect a possible opioid receptor-related interaction, an antagonist of the methoxymorphinane series (cyprodime 80 g/kg i.v.) with higher selectivity than naloxone for the mu-receptor was given at the end. RESULTS. Compared to controls, S(+)-ketamine induced a dose-related increase in output in the theta-(3-8 Hz) band and an increase in output in the alpha-domain (8-13 Hz) following 20 mg/kg. Both effects were reversed completely by the opioid antagonist. At low doses (2-5 mg/kg) there was an increase in output (P less than 0.05) in the beta-(13-30 Hz) and a concomitant decrease in output (P less than 0.05) in the delta-(0.5-3 Hz) band. These effects were reversed with increasing doses (5-10 mg/kg). After 20 mg/kg, however, output in the delta-domain increased while power in the beta band decreased significantly (P less than 0.005) when compared to controls. Both effects were reversed by the opioid antagonist. Compared to controls, the reversal resulted in a 12% increase in output in the beta- and a 49% decrease in output in the delta-domain. In SEP, S(+)-ketamine induced a dose-related increase in peak latency and depression of amplitude of more than 50% when compared to controls. While latency changes were completely reversed, amplitude height was only partly restored by the antagonist. Respiration was depressed in a dose-related fashion (PaO2 decreased, PaCO2 increased). Hypoxaemia was fully reversed by the antagonist; hypercapnia was only partly reversed. CONCLUSION. The results support the presumption that the S(+)-isomer of ketamine induces opioid mu-receptor-mediated central effects. Hypersynchronisation of the EEG suggests a deep plane of anaesthesia after S(+)-ketamine. The pronounced blockade of impulses in the sensory nervous pathways suggests an efficient analgesic effect that is partly mediated by the opioid-receptor. The respiratory depression may be of importance when S(+)-ketamine is used in high dosages in man.

Synthesis and biological evaluation of 14-alkoxymorphinans, V: 6-Deoxyocyprodime, an opioid antagonist with decreased mu receptor selectivity in comparison to cyprodime

N-Cyclopropylmethyl-4,14-dimethoxymorphinan (4) and N-cyclopropylmethyl-4-hydroxy-14-methoxymorphinan (5) have been prepared from cyprodime (1) by Wolff-Kishner reduction. Pharmacological studies (mouse vas deferens and guinea pig ileum preparations) revealed that there was no significant decrease of 4 in antagonist activity but in mu selectivity when compared with 1. The phenol 5 showed partial agonism at mu, kappa and delta receptors.

(-)-N,N'-but-2-ene-1,4-diylbimorphinans

N,N'-But-2-ene-1,4-diylbimorphinans 1-3 have been synthesized and pharmacologically evaluated. Bimorphinans 1 and 3 show opioid antagonist activity and preference for mu and kappa opioid receptors in mouse vas deferens and guinea pig ileum preparations.

Synthesis and biological evaluation of 14-alkoxymorphinans. 3. Extensive study on cyprodime-related compounds

A series of cyprodime-related compounds (2, 4-12, and 26) has been synthesized and evaluated for opioid agonist and antagonist activity with the mouse vas deferens and guinea pig ileum preparations. None of the changes to cyprodime, including the introduction of a 3-OMe group, increasing and decreasing the size of or completely removing the substituent in position 4, replacing the N-cyclopropylmethyl group with an N-allyl group, or replacing the 14-OMe with an 14-OEt substituent, resulted in an improved mu antagonist profile and most were detrimental either in terms of mu selectivity and potency or increased agonist activity. Increasing the length of the substituent in position 4 resulted in a compound (6a) with a very similar profile to that of cyprodime.

An opioid agonist with preference for kappa-opioid receptors: (-)-N-cyclopropylmethylmorphinan-6-one

N-Cyclopropylmethyl- and N-cyclobutylmethylmorphinan-6-one (3 and 4, respectively) were prepared from N-methylmorphinan-6-one. The pharmacological studies showed 3 and 4 to be potent opioid agonists. Compound 3 was found to have preference for kappa rather than mu opioid receptors.