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Abstract

Several studies have investigated stereochemical effects observed in the electron ionization and low-energy collision-induced dissociation (CID) mass spectra of molecular ions from synthetic and natural alkaloids. More recently, it has been shown that low-collision-energy CID spectra of protonated epimeric alkaloids can yield additional information. For instance, three epimeric tetracyclic alkaloids studied in the present work are characterized by different cis/trans ring junction geometries and by different configurations of the ethyl group linked to the C-ring. Low-energy collisional spectra of the epimeric MH+ ions show large differences depending both on the ring junction geometry and the stereochemistry of the side chain. Interpretation of certain specific processes invokes ion-dipole formation, allowing internal electron transfer. Consecutive decompositions have also been scrutinized.