Psychoactive substances of the 2C-series (2Cs) are
phenethylamine-derived
designer drugs that can induce psychostimulant and hallucinogenic effects. Chemically, the classic 2Cs contain two methoxy groups in positions 2 and 5 of the phenyl ring, whereas substances of the so-called FLY series contain rigidified methoxy groups integrated in a 2,3,6,7-tetrahydrobenzo[1,2-b:4,5-b']difuran core. One of the pharmacological features that has not been investigated in detail is the inhibition of
monoamine oxidase (
MAO). Inhibition of this
enzyme can cause elevated monoamine levels that have been associated with adverse events such as agitation,
nausea,
vomiting,
tachycardia,
hypertension, or
seizures. The aim of this study was to extend the knowledge surrounding the potential of
MAO inhibition for 17 test drugs, which consisted of 12 2Cs (2C-B, 2C-D, 2C-E, 2C-H, 2C-I, 2C-N, 2C-P, 2C-T-2, 2C-T-7, 2C-T-21, bk-2C-B, and bk-2C-I) and five FLY analogs (2C-B-FLY, 2C-E-FLY, 2C-EF-FLY, 2C-I-FLY, and 2C-T-7-FLY). The extent of
MAO inhibition was assessed using an established in vitro procedure based on heterologously expressed
enzymes and analysis by hydrophilic interaction liquid chromatography-high resolution tandem mass spectrometry. Thirteen test drugs showed inhibition potential for
MAO-A and 11 showed inhibition of
MAO-B. In cases where
MAO-A IC50 values were determined, values ranged from 10 to 125 μM (7 drugs) and from 1.7 to 180 μM for
MAO-B (9 drugs). In the absence of detailed clinical information on most test drugs, it is concluded that a pharmacological contribution of
MAO inhibition cannot be excluded and that further studies are warranted.