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| Other names | 4-API; 4-IT; α-Methylisotryptamine; α-Me-isotryptamine; α-Me-isoT |
| Drug class | Serotonin receptor modulator; Serotonin 5-HT2 receptor modulator; Monoamine oxidase inhibitor |
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| Formula | C11H14N2 |
| Molar mass | 174.247 g·mol−1 |
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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.1234 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).234 The drug is a sort of hybrid structure between phenethylamines and tryptamines.1234
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.34
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 1963.15 Subsequently, it was studied by Aurelio Cerletti and colleagues in 19682 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
References
References
- 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.
- 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.
- 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.
- 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.
- "Nouveaux dérivés de l'indole et leur préparation" [New indole derivatives and their preparation]. Google Patents. 21 November 1962. Retrieved 10 February 2026.