MASS-SPECTROMETRIC DIFFERENTIATION OF HUPERZININE, N,N-DIMETHYLHUPERZINE-A AND N-METHYLHUPERZINE-B

The newly isolated Lycopodium alkaloids huperzinine, N,N-dimethylhuperzine A and N-methylhuperzine B were studied by high-resolution and tandem mass spectrometry. Differentiation of these subtly different isomers from each other and from the general class of Lycopodium alkaloids can be achieved by taking advantage of the structure-specific fragment ions formed upon electron ionization (EI) or collisional activation of these alkaloids. Beta-Obscurine was identified as an impurity component in the N-methylhuperzine B sample and contributed to the EI mass spectrum. The previously published EI mass spectrum of N-methylhuperzine B is likely to be that of a mixture of N-methylhuperzine B and beta-obscurine. The presence of the impurity can now be readily recognized on the basis of two characteristic fragment ions of m/z 215 and 187.