Abstract
Chemical analysis of a southern Australian sponge, Leucetta sp., led to the discovery of a pair of solvolysis adducts, leucettazoles A1 (1a) and B1 (2a), as artifacts of an unprecedented family of 15-membered macrocyclic alkaloid dimers featuring a pair of imino bridged 2-aminoimidazoles, together with a putative monomeric precursor, leucettazine A (3). The dimeric alkaloids 1a and 2a, and monomer 3, were identified by detailed spectroscopic analysis, supported by chemical transformations, analytical mass spectrometry, and biosynthetic considerations. Global natural product social networking (GNPS) molecular analysis of crude sponge extracts and solvent partitions, supported by single ion extraction (SIE) and diagnostic MS/MS fragmentations, revealed the associated natural products, leucettazoles A (1) and B (2). This study highlights that the study of natural product artifacts can be useful, and can on occasion serve as a pathway to discover cryptic new classes of natural products.
Highlights
Marine sponges are a remarkable source of structurally diverse natural products
Extract a sponge sample partitions was decanted, in vacuo, and subjected to a of sequence of solvent and triturations, was decanted, concentrated HPLC, in vacuo, and leucettazoles subjected to A1 a sequence of (2a), solvent and followed by reversed-phase to yield
Knowledge of leucettazoles A (1) and B (2) is an intriguing late addition to our understanding of the natural product scaffolds embodied within southern Australian marine sponges, and the proposed biosynthesis provides useful insights into a prospective biomimetic synthesis
Summary
Marine sponges are a remarkable source of structurally diverse natural products. Over several decades, our investigation of southern Australian marine sponges revealed a wealth of natural product classes, many unique to marine sponges. These include the terpenyls luffarins [1]. During our studies into sponges, and other Australian marine biodiversity, we regularly encounter natural products that are prone to structural transformation during extraction, isolation, and/or handling. Such compounds, typically denoted as artifacts, enjoy a questionable presence in the field of natural products. Where some natural product chemists tend to ignore artifacts, opting instead to describe every isolated compound as a natural product, others are willing to acknowledge the presence of artifacts, but relegate them to inconsequential footnotes
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