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Not to be confused with α-Methylisotryptamine.

4-(2-Aminopropyl)indole (4-API), also known in the past as α-methylisotryptamine (α-Me-isoT), is a serotonin receptor modulator of the phenethylamine and amphetamine families.[1][2][3][4] It is one of seven possible positional isomers of (2-aminopropyl)indole (API), with other examples including α-methyltryptamine (AMT; 3-API) and α-methylisotryptamine (isoAMT; 1-API).[2][3][4] The drug is a sort of hybrid structure between phenethylamines and tryptamines.[1][2][3][4]

It shows affinity for the serotonin 5-HT2 receptor (Ki = 5,000 nM), with its affinity being only 2-fold lower than that of AMT (Ki = 2,500 nM) in the same study.[3] The drug reverses the facilitation of pentylenetetrazol-induced seizures evoked by the monoamine depleting agent reserpine in rodents, albeit with much lower potency than AMT (10-fold) and certain other API positional isomers.[2] It showed activity as a monoamine oxidase inhibitor (MAOI) in vitro, with slightly higher potency than AMT.[2]

The synthesis and identification of 4-API have been described.[3][4]

4-API was first described in the literature in a patent as a potential antiasthmatic agent by Albert Hofmann and Franz Troxler at Sandoz in 1963.[1][5] Subsequently, it was studied by Aurelio Cerletti and colleagues in 1968[2] and by Richard Glennon and colleagues in 1988.[3] The drug was referred to as “α-methyl-isotryptamine” or “α-Me-isoT” by Glennon and colleagues, but this term subsequently came to be used to refer to 1-API instead.[3] Certain APIs, such as AMT and 5-(2-aminopropyl)indole (5-API), have been encountered as novel designer drugs, but 4-API does not appear to have been encountered as of 2014.[4]

Chemical structures of selected APIs and related compounds

See also

References

  1. ^ a b c Trachsel D, Lehmann D, Enzensperger C (2013). Phenethylamine: von der Struktur zur Funktion [Phenethylamines: From Structure to Function]. Nachtschatten-Science (in German) (1 ed.). Solothurn: Nachtschatten-Verlag. p. 470. ISBN 978-3-03788-700-4. OCLC 858805226. Archived from the original on 21 August 2025. Compound 50 has an indole structure in which the alkylamine side chain is located at the 4-position, not at the 3-position as in tryptamine derivatives. On the one hand, the compound was mentioned in a 1963 patent by Hofmann and Troxler of the Sandoz company for possible use as an asthma treatment [48], and on the other hand, it was included in a SAR study on hydroxyindolealkylamines [49]. […] [48] A. Hofmann, F. Troxler. 4(or 5 or 6)-(2Aminoalkyl)indoles. FR1344579, 1963. [49] A. Cerletti, M. Taeschler, H. Weidmann. Adv. Pharmacol. 1968, 6, 233.
  2. ^ a b c d e f Cerletti A, Taeschler M, Weidmann H (1968). “Pharmacologic studies on the structure-activity relationship of hydroxyindole alkylamines”. Pharmacology, Behavior, and Clinical Aspects, Proceedings of a Symposium held at the College of Physicians and Surgeons, Columbia University, New York. Advances in Pharmacology. Vol. 6. pp. 233–246. doi:10.1016/s1054-3589(08)60322-1. ISBN 978-0-12-032906-9. PMID 5658327.
  3. ^ a b c d e f g Lyon RA, Titeler M, Seggel MR, Glennon RA (January 1988). “Indolealkylamine analogs share 5-HT2 binding characteristics with phenylalkylamine hallucinogens”. European Journal of Pharmacology. 145 (3): 291–297. doi:10.1016/0014-2999(88)90432-3. PMID 3350047.
  4. ^ a b c d e Scott KR, Power JD, McDermott SD, O’Brien JE, Talbot BN, Barry MG, et al. (2014). “Identification of (2-aminopropyl)indole positional isomers in forensic samples” (PDF). Drug Testing and Analysis. 6 (7–8): 598–606. doi:10.1002/dta.1508. PMID 23836607.
  5. ^ “Nouveaux dérivés de l’indole et leur préparation” [New indole derivatives and their preparation]. Google Patents. 21 November 1962. Retrieved 10 February 2026.