Some aspects of the chemistry of quaternary benzo[c]phenanthridine alkaloids

Abstract

Abstract Quaternary benzo[ c ]phenanthridine alkaloids (QBA)are a relatively small class of natural products. These isoquinoline-derived alkaloids are conspicuous for their bright colours. They currently number 18, apart from evident artifacts and synthetic derivatives. QBA are widely distributed in a number of plant species of the Papaveraceae, Fumariaceae , and Rutaceae families. The most abundant sources of QBA are Sanguinaria canadensis, Chelidonium majus, Dicranostigma lactucoides, Macleaya cordata, M. microcarpa , and some Bocconia and Zanthoxylum species. Sanguinarine and chelerythrine, discovered in the 19th century, are the two best-known and commercially available QBA. Quaternary benzophenathridine cations display great susceptibility towards nucleophilic reagents. This nucleophilic attack is associated with a number of significant alterations in physical appearance, solubility, constitution, spectral properties, etc. A specific and very interesting chapter in the chemistry of the QBA concerns the formation of free bases. In analkaline environment, QBA are converted to bimolecular aminoacetal derivatives with an oxygen atom as the linking bridge. This review describes the distribution of QBA in plants. Methods of isolation and separation are included as well as biological activities. The main part of this chapter is devoted to the chemical reactivity of QBA, nucleophilic transformations and the formation of free bases.