Abstract
Coniine, a polyketide-derived alkaloid, is poisonous to humans and animals. It is a nicotinic acetylcholine receptor antagonist, which leads to inhibition of the nervous system, eventually causing death by suffocation in mammals. Coniine’s most famous victim is Socrates who was sentenced to death by poison chalice containing poison hemlock in 399 BC. In chemistry, coniine holds two historical records: It is the first alkaloid the chemical structure of which was established (in 1881), and that was chemically synthesized (in 1886). In plants, coniine and twelve closely related alkaloids are known from poison hemlock (Conium maculatum L.), and several Sarracenia and Aloe species. Recent work confirmed its biosynthetic polyketide origin. Biosynthesis commences by carbon backbone formation from butyryl-CoA and two malonyl-CoA building blocks catalyzed by polyketide synthase. A transamination reaction incorporates nitrogen from l-alanine and non-enzymatic cyclization leads to γ-coniceine, the first hemlock alkaloid in the pathway. Ultimately, reduction of γ-coniceine to coniine is facilitated by NADPH-dependent γ-coniceine reductase. Although coniine is notorious for its toxicity, there is no consensus on its ecological roles, especially in the carnivorous pitcher plants where it occurs. Lately there has been renewed interest in coniine’s medical uses particularly for pain relief without an addictive side effect.
Highlights
Coniine is an alkaloid which is known to be present in a diversity of plants, including monocots (Aloe [1,2,3,4]) and dicots (Conium (e.g., [5]) and Sarracenia [6,7])
Coniine and twelve closely related alkaloids are known from poison hemlock (Conium maculatum L.), and several Sarracenia and Aloe species
Biosynthesis commences by carbon backbone formation from butyryl-CoA and two malonyl-CoA building blocks catalyzed by polyketide synthase
Summary
Coniine is an alkaloid which is known to be present in a diversity of plants, including monocots (Aloe [1,2,3,4]) and dicots (Conium (e.g., [5]) and Sarracenia [6,7]). Coniine holds two records in chemistry in that it constitutes the first alkaloid the structure of which was fully resolved, and that has been chemically synthesized. Coniine, have historically been used as medicine but not anymore due to a narrow treatment window. Coniine’s ecological role in plants, on the other hand, is not yet fully revealed, especially in insectivorous. The poison hemlock and coniine literature has been reviewed by López et al [8], Vetter [9] and Reynolds [10]. There have been many advances related to the biosynthesis, occurrence in plants, molecular diversity and biological interactions, justifying an updated summary
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