Structure elucidation of a new open chain isomer of the cannabimimetic cyclopropoylindole A-796,260

A new hitherto unknown ring opened isomer of the tetramethylcyclopropoylindole 1-(2-morpholin-4-ylethyl)-1H-indol-3-yl]-(2,2,3,3-tetramethylcyclopropyl)methanone (A-796,260) has been identified in a seizure of the German Customs. It bears an E-alkene moiety in the side chain with a tert.-butyl group, having a 3-penten-5-one skeleton. The isomer is not identical to the known products of thermal ring opening of tetramethylcyclopropoylindoles, which have a 1-pentene-5-one alkyl chain, instead. We postulate its formation via a Wagner-Meerwein-rearrangement under acidic conditions during the attempted synthesis of the desired tetramethylcyclopropoylindole. Whether the compound, found in high purity, has been the result of a synthesis fault or has been synthesized intentionally and if the new isomer has cannabimimetic potential, is still unknown. During structure elucidation with NMR spectroscopy and mass spectrometry, interesting phenomena have been detected concerning the product ion spectrometry of tetramethylcyclopropoylindoles.