No abstract

Biotransformation of deuterated-4'-O-methylnorbelladine into alkaloids galanthamine and lycorine in tissue cultures of Leucojum aestivum was demonstrated using HPLC coupled to mass spectrometry. GC-MS screening was also carried to investigate other native and deuterated alkaloids. A total of six labeled alkaloids were identified indicating that 4'-O-methyl-d(3)-norbelladine is incorporated into three different groups of Amaryllidaceae alkaloids that are biosynthesized by three modes of intramolecular oxidative phenol coupling.

Galanthamine, an isoquinoline alkaloid acetylcholinesterase inhibitor, is an important agent used all around the world for the symptomatic treatment of senile dementia of the Alzheimer's type. The production of this metabolite and the availability of the plant are limited and prompted the search for an alternative way to obtain this valuable metabolite using in vitro cultures of Leucojum aestivum L. It is known that cell differentiation level shows a major influence upon the accumulation of alkaloids. For this reason, tissue cultures of L. aestivum showing different stages of morphogenesis controlled by exogenous growth regulators were established. Agrobacterium rhizogenes strain LBA 9402 has been tested for its capacity to induce hairy roots of this monocotyledonae plant.

Condensation of functionalized o-toluamide anions on a carbohydrate-derived lactone, followed by intramolecular aldol cyclization, provides enantiomerically pure 2-arylcyclohexenones. Different approaches for the stereoselective transformation of the carbonyl group of these key intermediates into an amino group were unsuccessful. However 1,4-addition of thiolate and concomitant ring closure to isocoumarine provided a useful method for the transformation of the tertiary amide function. Opening of the isocoumarin with ammonia provided the corresponding amide and recovery of the enone system. Subsequent reductive amination of this cyclohexenone was found to depend on the nature of the protecting groups and led to the protected form of 4-epi- and -iso-narciclasine. Oxo analogues of narciclasine and epi-narciclasine and lycoricidine were also obtained after reduction of the enone and subsequent lactonization. They showed no biological activity as antitumor agents.

Plants of the genus Amaryllidaceae produce a number of alkaloids and other non-basic related molecules, some of them showing antitumor activities. The low availability of these often-complex structures, coupled with their interesting biological properties, has stimulated a long-standing interest in the chemistry community. Total syntheses of challenging structures such as lycoricidine, narciclasine and pancratistatin, which are highly oxygenated tetracyclic systems comprising up to six contiguous chiral centers on ring C, have been accomplished. These well-known structures, more than thirty years for lycoricidine, continue to stimulate interest in synthetic work to provide enough synthetic material or analogs, and also are a model target to test or develop new synthetic methodologies. The synthetic studies around these complex phenanthridinones made use of the latest up-to-date synthetic methodologies and led to the development of novel methods of functionalization and carbon-carbon bond formation. The purpose of this review is to summarize recent total syntheses and synthetic approaches towards these three highly oxygenated members of this particular class of alkaloids over the last twenty years. The review is arranged according to the different strategies used for the construction of the benzophenanthridinone ring system.