Alkylamines, pharmacological activity

The primary pharmacologic activity of promethazine is that of an antihistamine, whereas promazine is an antipsychotic. The only difference between the two is the alkylamine side chain. In the case of promethazine, it contains a isopropylamine side chain, whereas promazine has a n-propylamine. In this case, the small change of one carbon atom from a branched to a linear hydrocarbon radically alters the pharmacologic activity. 

Cerletti, A., Taeschler, M., and Weidmann, H. (1968) Pharmacologic studies on the structure-activity relationship of hydroxyindole alkylamines. Adv. Pharmacol., 6B.233-246. 

N,N-Dimethylttyptamine (DMT) is a representative of the tryptamin i.e. indole-3-alkylamine, family. Note the stmc-tural similarity to serotonin which is 5-hydroxyttyptamine (Fig. 18.33). DMT is parenterally, but not orally, active at around 60-100 mg of the free base since rapid deamination by monoamine oxidase oteurs following oral administration. Pharmacological effects are therefore induced by inhalation of the free base vapour or by injection of a water-soluble salt. The fumarate salt has been used in a number of human dinical studies and it was reported that the psychoactive effects are relativdy short-lived, with durations less than 1 horn. Smoking of the free base leads to very intense but short-lived effects for around 5-15 minutes. A number of N-mono and dimethylated tryptamines are also present in several human tissues. Thdr exact function has been debated for several decades but so far no definite condusion has been reached. 

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