PMMA-stimulus generalization to the optical isomers of MBDB and 3,4-DMA

Beyond ecstasy: Alternative entactogens to 3,4-methylenedioxymethamphetamine with potential applications in psychotherapy

The last two decades have seen a revival of interest in the entactogen 3,4-methylenedioxy-N-methylamphetamine (MDMA) as an adjunct to psychotherapy, particularly for the treatment of post-traumatic stress disorder. While clinical results are highly promising, and MDMA is expected to be approved as a treatment in the near future, it is currently the only compound in its class of action that is being actively investigated as a medicine. This lack of alternatives to MDMA may prove detrimental to patients who do not respond well to the particular mechanism of action of MDMA or whose treatment calls for a modification of MDMA's effects. For instance, patients with existing cardiovascular conditions or with a prolonged history of stimulant drug use may not fit into the current model of MDMA-assisted psychotherapy, and could benefit from alternative drugs. This review examines the existing literature on a host of entactogenic drugs, which may prove to be useful alternatives in the future, paying particularly close attention to any neurotoxic risks, neuropharmacological mechanism of action and entactogenic commonalities with MDMA. The substances examined derive from the 1,3-benzodioxole, cathinone, benzofuran, aminoindane, indole and amphetamine classes. Several compounds from these classes are identified as potential alternatives to MDMA.

Emergence and properties of spice and bath salts: a medicinal chemistry perspective

Over the past five years the number of internet sites advertising "legal highs" has literally exploded, as have user reports of experiences (both pleasurable and frightening) with these substances and the number of emergency room visits by users. Although the majority of these "legal highs" have been described as bath salts and herbal extracts, most contain neither plant derived compounds nor components of personal hygiene products. So-called "bath salts" largely contain synthetic analogs of the natural compound Khat; spice-related materials, claimed to be "legal marijuana," are mostly synthetic analogs of cannabinoid receptor ligands that were developed as research tools. This review describes the emergence and properties of these two groups of "legal highs" from a medicinal chemist's perspective.

N-Methyl-1-(4-methoxyphenyl)-2-aminopropane (PMMA) and N-Methyl-1-(3,4-methylenedioxyphenyl)-2-aminopropane (MDMA) produce non-identical discriminative stimuli in rats

N-Methyl-1-(3,4-methylenedioxyphenyl)-2-aminopropane (methylenedioxymethamphetamine, MDMA, Ecstasy) and its structurally abbreviated congener N-methyl-1-(4-methoxyphenyl)-2-aminopropane (para-methoxymethamphetamine, PMMA) are chemically related designer drugs, and PMMA is sometimes sold on the clandestine market as a substitute for MDMA. Prior drug discrimination studies have found that MDMA and PMMA substitute for one another suggesting that they produce similar discriminative stimulus effects in rats. However, there also are some indications that the two agents produce distinct stimulus effects. In this study, further comparisons were made between the stimulus effects of these two agents. Sprague-Dawley rats were trained to discriminate either 1.25 mg/kg of PMMA or 1.5 mg/kg of MDMA from saline vehicle in a two-lever operant paradigm. A structure-activity comparison revealed that MDMA and PMMA behave similarly upon homologation of their terminal amine substituents. In contrast, the PMMA stimulus, unlike an MDMA stimulus, failed to generalize completely to the psychostimulant cocaine, 8-hydroxy-2-(N,N-di-n-propylamino)tetralin (8-OH DPAT), and R(-)-1-(3-methoxyphenyl)-2-aminopropane [R(-)MMA]. In an additional group of animals, a (+)amphetamine stimulus partially generalized to R(-)MMA. Taken together, the results argue and re-emphasize the conclusion that the stimulus effects produced by MDMA and PMMA are similar, but non-identical, and that PMMA is the less "stimulant-like" of the two.

IDENTIFICATION OF HUMAN CYTOCHROME P450 2D6 AS MAJOR ENZYME INVOLVED IN THEO-DEMETHYLATION OF THE DESIGNER DRUGP-METHOXYMETHAMPHETAMINE

p-Methoxymethamphetamine (PMMA) is a new designer drug, listed in many countries as a controlled substance. Several fatalities have been attributed to the abuse of this designer drug. Previous in vivo studies using Wistar rats had shown that PMMA was metabolized mainly by O-demethylation. The aim of the study presented here was to identify the human hepatic cytochrome P450 (P450) enzymes involved in the biotransformation of PMMA to p-hydroxymethamphetamine. Baculovirus-infected insect cell microsomes, pooled human liver microsomes (pHLMs), and CYP2D6 poor-metabolizer genotype human liver microsomes (PM HLMs) were used for this purpose. Only CYP2D6 catalyzed O-demethylation. The apparent K(m) and V(max) values in baculovirus-infected insect cell microsomes were 4.6 +/- 1.0 microM and 92.0 +/- 3.7 pmol/min/pmol P450, respectively, and 42.0 +/- 4.0 microM and 412.5 +/- 10.8 pmol/min/mg protein in pHLMs. Inhibition studies with 1 microM quinidine showed significant inhibition of the metabolite formation (67.2 +/- 0.6%; p < 0.0001), and comparison of the metabolite formation between pHLMs and PM HLMs revealed significantly lower metabolite formation in the incubations with PM HLMs (87.3 +/- 1.1%; p < 0.0001). According to these studies, CYP2D6 is the major P450 involved in O-demethylation of PMMA.

Effect of 1-(3,4-methylenedioxyphenyl)-2-aminopropane and its optical isomers in PMMA-trained rats

1-(3,4-Methylenedioxyphenyl)-2-aminopropane (MDA) is a drug of abuse that is known to produce stimulus effects similar to those of the stimulant phenylalkylamine (+)amphetamine and the hallucinogenic phenylalkylamine 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM). Earlier, a working model was described to account for the stimulus effects produced by phenylalkylamines. Such agents can produce one or more of three distinct effects: an amphetamine effect, a DOM effect and a third effect that is typified by the agent N-methyl-1-(4-methoxyphenyl)-2-aminopropane (PMMA). Because MDA is known to produce two of the three effects, in the present investigation, we sought to determine if racemic MDA or either of its optical isomers could produce a PMMA-like effect in animals. Administration of S(+)MDA, R(-)MDA and (+/-)MDA to rats trained to discriminate 1.25 mg/kg of PMMA from saline vehicle under a VI 15-s schedule of reinforcement resulted in substitution in each case. (+/-)MDA and S(+)MDA were nearly equipotent and several fold more potent than R(-)MDA. The results are not only consistent with the proposed model but also identify (+/-)MDA as the first phenylalkylamine shown to produce all three types of stimulus effects (i.e., amphetamine-like, DOM-like and PMMA-like) in rats.

Effect of PMA optical isomers and 4-MTA in PMMA-trained rats

1-(4-Methoxyphenyl)-2-aminopropane (PMA) and its sulfur analog, 1-(4-methylthiophenyl)-2-aminopropane (4-MTA), have been misrepresented as the controlled substance analog, N-methyl-1-(3,4-methylenedioxyphenyl)-2-aminopropane (MDMA; "Ecstasy"). Because MDMA has been shown to produce both amphetamine-like and N-methyl-1-(4-methoxyphenyl)-2-aminopropane (PMMA)-like stimulus effects in rats, we examined S(+)PMA, R(-)PMA and 4-MTA in rats trained to discriminate either PMMA (1.25 mg/kg) or (+)amphetamine (1.0 mg/kg) from saline vehicle. The sulfur analog of PMMA (i.e., 4-MTMA) was also examined. The PMMA stimulus generalized to R(-)PMA (ED50=0.4 mg/kg), whereas S(+)PMA produced a maximum of 72% PMMA-appropriate responding. 4-MTA (ED50=0.3 mg/kg) also substituted for PMMA, but 4-MTMA produced a maximum of only 36% PMMA-appropriate responding. None of the four agents substituted for (+)amphetamine. Hence, like MDMA, R(-)PMA and 4-MTA are capable of producing PMMA stimulus effects in rats, but unlike MDMA, neither agent substituted for (+)amphetamine.

Further characterization of the stimulus properties of 5,6,7,8-tetrahydro-1,3-dioxolo[4,5-g]isoquinoline

This investigation is based on the premise that conformational restriction of abused phenylalkylamines in a tetrahydroisoquinoline conformation alters their pharmacology in such a manner that their original action is lost and that a new action emerges. TDIQ or 5,6,7,8-tetrahydro-1,3-dioxolo[4,5-g]isoquinoline, is a conformationally constrained phenylalkylamine that serves as a discriminative stimulus in animals. Although TDIQ bears structural resemblance to phenylalkylamine stimulants (e.g., amphetamine), hallucinogens (e.g., 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane [DOM]), and designer drugs (e.g., N-methyl-1-(3,4-methylenedioxyphenyl)-2-aminopropane [MDMA], N-methyl-1-(4-methoxyphenyl)-2-aminopropane [PMMA]), the TDIQ stimulus failed to generalize to (+)amphetamine or MDMA. In the present investigation, further evaluations were made of the stimulus nature of TDIQ. Specifically, the stimulus similarities of TDIQ, PMMA, and DOM were examined. In no case was stimulus generalization (substitution) observed. The results confirm that TDIQ produces stimulus effects distinct from those of the abovementioned phenylalkylamines. We also examined the structure-activity relationships of a series of TDIQ analogs, including several that might be viewed as conformationally restricted (CR) analogs of phenylalkylamine hallucinogens, stimulants, and designer drugs. These agents were examined in rats trained to discriminate either DOM (1.0 mg/kg), (+)amphetamine (1.0 mg/kg), MDMA (1.5 mg/kg), or TDIQ (5.0 mg/kg) from saline vehicle. Whereas we have demonstrated that none of these agents retains their respective phenylalkylamine stimulus actions, several of these agents were found to substitute for TDIQ. N-Methylation abolished TDIQ-stimulus action. These results, coupled with previous findings, imply that TDIQ derivatives represent a novel class of phenylalkylamines analogs with unique stimulus properties. Preliminary radioligand binding studies suggest that an alpha2-adrenergic mechanism might underlie the stimulus effects produced by TDIQ.

Discriminative stimulus properties of alpha-ethyltryptamine optical isomers

alpha-Ethyltryptamine (alpha-ET) possesses central stimulant and hallucinogenic activity. Also, in tests of stimulus generalization using rats trained to discriminate the controlled substance analog (i.e., designer drug) N-methyl-1-(3,4-methylenedioxyphenyl)-2-aminopropane (MDMA) from vehicle, alpha-ET substituted for MDMA. These previous studies employed racemic alpha-ET. Because psychoactive phenylalkylamines with abuse potential can produce one or more of three distinct stimulus effects (i.e., amphetamine-, DOM- and/or PMMA-like effects) in animals trained to discriminate either the stimulant (+)amphetamine, the hallucinogen 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM), or N-methyl-1-(4-methoxyphenyl)-2-aminopropane (PMMA) from vehicle, and because these effects can be stereoselective, the individual optical isomers of alpha-ET were examined in groups of animals trained to discriminate (+)amphetamine, DOM, PMMA and MDMA from saline vehicle. (-)alpha-ET (ED(50)=7.8 mg/kg), but not (+)alpha-ET (maximum of 53% drug-appropriate responding), substituted for (+)amphetamine, whereas (+)alpha-ET (ED(50)=2.7 mg/kg), but not (-)alpha-ET (maximum of 33% drug-appropriate responding), substituted for DOM. Both optical isomers of alpha-ET substituted for PMMA and MDMA with ED(50) values of 1.6 and 1.4 mg/kg (PMMA-trained animals) and 1.3 and 2.0 mg/kg (MDMA-trained animals) for (-)alpha-ET and (+)alpha-ET, respectively. The results of this investigation suggest that both optical isomers of alpha-ET are capable of producing an MDMA/PMMA-like effect at nearly comparable doses, and that the stimulant or amphetamine-like nature of alpha-ET resides primarily with its (-)isomer whereas hallucinogenic or DOM-like character resides primarily with the (+)enantiomer.