Biosynthesis and biomimetic synthesis of alkaloids isolated from plants of the Nitraria and Myrioneuron genera: an unusual lysine-based metabolism

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Abstract

This review describes a wide panel of alkaloids isolated from plants of the Nitraria genus, focusing on their biosynthesis and discussing the resulting biomimetic chemistry in relevant cases. The scope is purposely limited to alkaloids derived at least to some extent from L-lysine, considering that most of these molecules have unique structures and are specific to the genus. Some of the biosynthetic pathways described are taken from the literature, but others are proposed here for the first time. The latter are mostly hypotheses justified by the fact that they are based on metabolic routes frequently encountered for other Nitraria alkaloids, and thus permit unification of the biosynthesis around common pivotal biosynthetic intermediates. Myrioneuron alkaloids are also presented as a newly discovered class with striking similarities to Nitraria alkaloids.

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Tangutorine induces p21 expression and abnormal mitosis in human colon cancer HT-29 cells.

B.P.L. Liu, E.Y.Y. Chong, F.W.K. Cheung … (2005)

A novel beta-carboline alkaloid, tangutorine (benz[f]indolo[2,3-a]quinolizidine) was isolated from the leaves of Nitraria tangutorum L. [Duan JA, Williams ID, Che CT, Zhou RH, Zhao RH, Tangutorine: a novel beta-carboline alkaloid from Nitraria tangutorum. Tetrahedron Lett 1999;40:2593-6], and its unique structural characters led us to initiate a study of its potential anti-proliferation activity. The in vitro treatment with low doses of tangutorine slightly stimulated the proliferation of human colon cancer HT29 cells until at concentrations higher than 6.25 microg/ml when the cell numbers, cellular MTT reduction, and cell proliferation by 3H-thymidine incorporation decreased in a dose-dependent manner (IC50=15 microg/ml=48 microM). Morphological studies of cells by fluorescence and electron microscopy did not show features for apoptosis but only large vacuoles, swollen mitochondria and dense cytoskeletal filaments bunching in the cytoplasm. Immunoblotting analysis revealed a dramatic induction of cyclin kinase inhibitor p21 as well as an inhibition of topoisomerase II expression at 25 microg/ml tangutorine, thereby impeding cell progression from S to G2/M phase. Cells accumulated at G1 phase of the cell cycle at concentrations > or =50 microg/ml tangutorine. Interestingly, some cells escaped from prolonged growth arrest without cell division and resulted in binucleated and polyploid G1 cells. Taken all results together, tangutorine induced a p21 suppression of all cyclins and their associated kinases, such as the topoisomerase II, and thus inhibited normal DNA replication and mitosis.

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Biomimetic synthesis of tangutorine following new biogenetic proposals.

Rim Salame, Edmond Gravel, Karine Leblanc … (2009)

Following new biosynthetic proposals, an expeditious synthesis of tangutorine, an indolic alkaloid from Nitraria tangutorum has been achieved in three steps from simple C(5) lysine-derived units. The work also includes further insights into the biosynthesis of Nitraria alkaloids.