6-APB (6-(2-aminopropyl)benzofuran) is an empathogenic psychoactive compound of the substituted benzofuran, substituted amphetamine and substituted phenethylamine classes. 6-APB and other compounds are sometimes informally called "Benzofury" in newspaper reports. It is similar in structure to MDA, but differs in that the 3,4-methylenedioxyphenyl ring system has been replaced with a benzofuran ring. 6-APB is also the unsaturated benzofuran derivative of 6-APDB. It may appear as a tan grainy powder. 6-APB was first synthesized by David Nichols and his team in 1993 while studying non-neurotoxic analogs of MDMA.
While the drug never became particularly popular, it briefly entered the rave and underground clubbing scene in the UK before its sale and import were banned. It falls under the category of research chemicals, sometimes called "legal highs." Because 6-APB and other substituted benzofurans have not been explicitly outlawed in some countries, they are often technically legal, contributing to their popularity.
6-APB is a serotonin–norepinephrine–dopamine reuptake inhibitor (SNDRI) with Ki values of 117, 150, and 2698 nM for the norepinephrine transporter (NET), dopamine transporter (DAT), and serotonin transporter (SERT), respectively. In addition, 6-APB not only blocks the reuptake of these monoamine neurotransmitters but is also a releasing agent of them; that is, it is a serotonin-norepinephrine-dopamine releasing agent (SNDRA). In addition to actions at the monoamine transporters, 6-APB is a potent full agonist of the serotonin 5-HT2B receptor (Ki = 3.7 nM), with higher affinity for this target than any other site. Moreover, unlike MDMA, 6-APB shows 100-fold selectivity for the 5-HT2B receptor over the 5-HT2A and 5-HT2C receptors. It is notably both more potent and more selective as an agonist of the 5-HT2B receptor than the reference 5-HT2B receptor agonist, BW-723C86, which is commonly used for research into the 5-HT2B receptor. Aside from the 5-HT2B receptor, 6-APB has also been found to bind with high affinity to the α2C-adrenergic receptor subtype (Ki = 45 nM), although the clinical significance of this action is unknown. 6-APB showed little other affinity at a wide selection of other sites.
The potent agonism of the 5-HT2B receptor makes it likely that 6-APB would be cardiotoxic with chronic or long-term use, as seen with other 5-HT2B receptor agonists such as the withdrawn serotonergic anorectic fenfluramine.
The pharmacokinetics of 6-APB have not been studied, however, some information can be extracted from user reports. These suggest an slow onset of 20–120 minutes. The drugs maximum effects last 3–4 hours, followed by a comedown phase of up to 24 hours.
Although limited literature is available, there is some data on metabolism of 6-APB in rats. Its Phase I metabolism involves hydroxylation of the furan ring, then cleavage of the ring, followed by a reduction of the unsaturated aldehyde from the previous step. The resulting aldehyde may then takes two paths. It is either oxidized to a carboxylic acid or reduced to an alcohol, and then hydroxylated. Phase II metabolism consists of glucuronidation. The most prevalent metabolites in rats were 3-carboxymethyl-4-hydroxyamphetamine and 4-carboxymethyl-3-hydroxyamphetamine.
6-APB and its structural isomer 5-APB have been tested with a series of agents including: Marquis, Liebermann, Mecke, and Froehde reagents. Exposing compounds to the reagents gives a colour change which is indicative of the compound under test.
6-APB succinate is reported to be practically insoluble in CHCl3 as well as very minimally soluble in cold water. A batch seized by the DEA contained a 2:1 ratio of succinate to 6-APB.
Exact experimental details are not provided, but roughly follow the provided procedure. The procedure of Briner et al. was the most comprehensive thus far and was replicated by Casale and Hays as described below.
Briefly, 3-bromophenol was refluxed with bromoacetaldehyde and NaH to give the diethyl acetyl, which then was heated with polyphosphoric acid to give a mixture of bromobenzofurans structural isomers: 4-Bromo-1-benzofuran and 6-Bromo-1-benzofuran. Both isomers were separated via silica gel column chromatography, then catalytically converted to their respective 2-propanones, and then reductively aminated to 6-APB and 4-APB. Both of which were converted to their HCl ion-pairs for further examination.
Users report a feeling a sense of euphoria and energy. The effect has been most closely compared with those of ecstasy. Adverse effects include loss of appetite, hallucinations, paranoia, tachycardia, insomnia, and jaw tension.
6-APB is Schedule III in Canada as it is an analogue of MDA. The CDSA was updated as a result of the Safe Streets Act changing amphetamines from Schedule 3 to Schedule 1.
6-APB is unscheduled in France.
6-APB is illegal in Italy.
6-APB is illegal in Germany since the 17th of July, 2013, when it was added to Anlage II of the Betäubungsmittelgesetz.
6-APB is not listed under the Opium Law or the Medicine Act in the Netherlands, and thus currently legal.
Certain countries contain a "substantially similar" catch-all clause in their drug law, such as New Zealand and Australia. This includes 6-APB as it is similar in chemical structure to the class A drug MDA, meaning 6-APB may be viewed as a controlled substance analogue in these jurisdictions.
In Sweden, as of 27 December 2009 6-APB is classified as "health hazard" under the act Lagen om förbud mot vissa hälsofarliga varor (translated Act on the Prohibition of Certain Goods Dangerous to Health).
On June 10, 2013 6-APB and a number of analogues were classified as Temporary Class Drugs in the UK following an ACMD recommendation. This means that sale and import of the named substances are criminal offences and are treated as for class B drugs. On November 28, 2013 the ACMD recommended that 6-APB and related benzofurans should become Class B, Schedule 1 substances. On March 5, 2014 the UK Home Office announced that 6-APB would be made a class B drug on 10 June 2014 alongside every other benzofuran entactogen and many structurally related drugs.
6-APB is unscheduled in the United States, but not currently approved by the Food and Drug Administration for human consumption.