Stephanie A. Sweetana’s research while affiliated with Purdue University West Lafayette and other places

Twenty new alkaloids, of which 13 are new natural products, have been discovered in Pachycereus weberi by tandem mass spectrometry using a mass-analyzed ion kinetic energy spectrometer. These observations have been confirmed by chromatography and, in many cases, by simple synthetic interconversions from known alkaloids. Particularly significant to the discovery of several alkaloids having the same molecular formula. Isomer distinctions such as these, which are difficult to make on pure compounds by mass spectrometry, were made by utilizing daughter spectra recorded successively during the evaporation of the material from the probe and/or from spectra recorded on different types of plant extracts. This study suggests that many natural materials may contain trace amounts of compounds of potential biomedical or synthetic interest and, in particular, that the number of known alkaloids might be greatly increased by experiments of this type.

Tandem mass spectrometry, applied to simple extracts of Backebergia militaris, indicated the presence of a number of new alkaloids, including fully aromatic oxygenated isoquinolines, their di- and tetra-hydro analogs, and beta-phenethylamines. These conclusions were supported by separation using radial tlc and comparison with authentic compounds. Traces of seven alkaloids new to this cactus species were identified; four (3,4,8,11) were known previously from other cacti. Three novel cactus alkaloids were identified and confirmed by synthesis as 7,8-dimethoxy-3,4-dihydroisoquinoline (12, dehydrolemaireocereine), 6,7-dimethoxyisoquinoline (13, backebergine), and 7,8-dimethoxyisoquinoline (14, isobackebergine). The last two compounds are the first simple, fully aromatic, isoquinoline alkaloids to be reported from the Cactaceae. The sensitivity of this approach to new alkaloid discovery is emphasized; the entire project consumed only 10 g of dried plant material.