Abstract
Alkaloids from plants are characterised by structural diversity and bioactivity, and maintain a privileged position in both modern and traditional medicines. In recent years, there have been significant advances in elucidating the biosynthetic origins of plant alkaloids. In this review, I will describe the progress made in determining the metabolic origins of the so-called true alkaloids, specialised metabolites derived from amino acids containing a nitrogen heterocycle. By identifying key biosynthetic steps that feature in the majority of pathways, I highlight the key roles played by modifications to primary metabolism, iminium reactivity and spontaneous reactions in the molecular and evolutionary origins of these pathways.
Highlights
De nition of alkaloids Major alkaloid classes Patterns in biosynthesis Amine accumulation Polyamines Putrescine Cadaverine Homospermidine Aromatic amines Tyrosine Tryptophan Summary Aldehyde accumulation Amino aldehydes N-Methylaminobutanal and N-methylpyrrolinium 5-Aminopentanal and D1-piperideine 4-(4-Oxobutylamino)butanal and pyrrolizidine Amino acid origins Phenylacetaldehydes Betalamic acid Phenylpropanoids Benzaldehydes Dihydrocinnamaldehyes Secologanin Iminium formation Intramolecular Intermolecular Coupled reactions Stable iminium
In the general pattern of alkaloid biosynthesis proposed in this review, amines accumulate beyond typical concentrations to enable ux to be directed into alkaloid metabolism without disruption to existing pathways
Whilst further veri cation is needed of this chronology, it suggests that amine accumulation pre gures the emergence of alkaloid biosynthesis
Summary
Background De nition of alkaloids Major alkaloid classes Patterns in biosynthesis Amine accumulation Polyamines Putrescine Cadaverine Homospermidine Aromatic amines Tyrosine Tryptophan Summary Aldehyde accumulation Amino aldehydes N-Methylaminobutanal and N-methylpyrrolinium 5-Aminopentanal and D1-piperideine 4-(4-Oxobutylamino)butanal and pyrrolizidine Amino acid origins Phenylacetaldehydes Betalamic acid Phenylpropanoids Benzaldehydes Dihydrocinnamaldehyes Secologanin Iminium formation Intramolecular Intermolecular Coupled reactions Stable iminium
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