Identification of (1H-indol-3-yl)(2,2,3,3-tetramethylcyclopropyl)methanone (DP-UR-144) in a herbal drug product that was commercially available in the Tokyo metropolitan area

We encountered during our investigation a case of herbal drug products commercially available in the Tokyo metropolitan area in 2014, in which a small unknown peak was detected, along with the intense peak of FUB-144, by liquid chromatography–ultraviolet detection. The present study was conducted to identify and clarify the pharmacological characteristics of the compound present in this small peak. We isolated a compound using a silica gel column from the peak, which was then identified to have a molecular weight of 241 Da by liquid chromatography–mass spectrometry and gas chromatography–mass spectrometry. The accurate mass measurement suggested an elementary composition of C16H19NO. Using these mass data together with those obtained by the nuclear magnetic resonance analysis, the compound was finally identified as (1H-indol-3-yl)(2,2,3,3-tetramethylcyclopropyl)methanone (despentyl-UR-144; DP-UR-144). In addition, this compound was revealed to have affinities for cannabinoid receptors CB1 and CB2 with EC50s of 2.36 × 10−6 and 2.79 × 10−8 M, respectively. To our knowledge, there is no information in the scientific literature on structural or pharmacological properties of this chemical. These results suggest that the components present in small amounts can contribute to the effects of a major component in their mother product, if they have sufficient pharmacological activities, and, therefore, even such small amounts of components should be precisely characterized and well evaluated to control illegal and potentially illegal drug products.