The plausible biogenetic mechanism proposed in this communication clarifies the chemical pathway leading to over 60 polycyclic pyrrole‐imidazole marine alkaloids isolated from more than 20 different species of various genera (Agelas, Hymeniacidon, Axinella, Acanthella, Cymbastella, Phakellia...) of sponges. The tautomerism and ambivalent reactivity of 2‐aminoimidazole precursors provide a consistent chemical pathway explaining the intriguing formation of all the compounds of this class. The mechanistic proposal proposed here for the first time is unique in the sense that the chemical pathway is universal and therefore provides fertile intellectual ground for the study of the enzymatic mechanism involved in this system.
The pyrrole-2-aminoimidazole (P-2-AI) alkaloids are a growing family of marine alkaloids, now numbering well over 150 members, with high topographical and biological information content. Their intriguing structural complexity, rich and compact stereochemical content, high N to C ratio (~1:2), and increasingly studied biological activities are attracting a growing number of researchers from numerous disciplines world-wide. This review surveys advances in this area with a focus on the structural diversity, biosynthetic hypotheses with increasing but still rare verifying experimental studies, asymmetric syntheses, and biological studies including cellular target receptor isolation studies of this stimulating and exciting alkaloid family.
A novel method of transamidation of carboxamides with amines using catalytic amounts of readily available boric acid under solvent-free conditions has been developed. The scope of the methodology has been demonstrated with (i) primary, secondary, and tertiary amides and phthalimide and (ii) aliphatic, aromatic, cyclic, acyclic, primary, and secondary amines.
The study of the n-butanol extract of the New Caledonian sponge Agelas dendromorpha led to the isolation and identification of three new pyrrole-2-aminoimidazole (P-2-AI) alkaloids, named agelastatins E (3) and F (4) and benzosceptrin C (5), together with 10 known metabolites, agelastatin A (1), agelastatin D (2), sceptrin (6), manzacidin A, tauroacidin A, taurodispacamide A, nortopsentin D, thymine, longamide, and 4,5-dibromopyrrole-2-carboxamide. Their structures were assigned by spectroscopic data interpretation. All the compounds were tested for cytotoxic activity.
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