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Abstract:

Cyclic lipopeptides (CLiPs) are secondary metabolites secreted by a range of bacterial phyla. CLiPs from Pseudomonas in particular display diverse structural variations in terms of the number of amino acid residues, macrocycle size, amino acid identity and stereochemistry (e.g. D- vs. L-amino acids). Reports detailing the discovery of novel or already characterized CLiPs from new sources appear regularly in literature. Increasingly however, the lack of detailed characterization threatens to cause considerable confusion, especially if configurational heterogeneity is present for one or more amino acids. Using Pseudomonas CLiPs from the Bananamide, Orfamide and Xantholysin groups as test cases, we demonstrate and validate that 1 H and 13 C NMR chemical shifts of CLiPs are sufficiently sensitive to differentiate between possible diastereomers of a particular sequence even when they only differ in a single D/L configuration. Rapid screening, involving simple comparison of the NMR fingerprint of a newly isolated CLiP with that of a reference CLiP of known stereochemistry, can then be applied to resolve dead-ends in configurational characterization and avoid the much more cumbersome chemical characterization protocols. Even when the stereochemistry of a particular reference CLiP remains to be established, NMR fingerprinting still allows verifying whether a CLiP from a novel source is already present in the reference collection, thus contributing to dereplication. To benefit research involving CLiPs, we have made a publicly available ‘knowledge base’ at https://www.rhizoclip.be , where we present an overview of published NMR fingerprint data of characterized CLiPs, together with literature data on the originally determined structures.

Significance Statement