A Molecular Networking Based Discovery of Diketopiperazine Heterodimers and Aspergillicins from <i>Aspergillus caelatus</i>

The number of species in Aspergillus section Flavi has recently increased to 36 and includes some of the most important and well-known species in the genus Aspergillus. Numerous secondary metabolites, especially mycotoxins, have been reported from species such as A. flavus; however many of the more recently described species are less studied from a chemical point of view. This paper describes the use of MS/MS-based molecular networking to investigate the metabolome of A. caelatus leading to the discovery of several new diketopiperazine dimers and aspergillicins. An MS-guided isolation procedure yielded six new compounds, including asperazines D-H (1-5) and aspergillicin H (6). Asperazines G and H are artifacts derived from asperazines E and F formed during the separation process by formic acid. Two known compounds, aspergillicins A and C (7 and 8), were isolated from the same strain. Structures were elucidated by analyzing their HR-MS/MS and NMR spectroscopic data. The absolute configuration of asperazines D-F and aspergillicin H were deduced from the combination of NMR, Marfey's method, and ECD analyses.