Determination of peptaibol trace amounts in marine sediments by liquid chromatography/electrospray ionization-ion trap-mass spectrometry

Metabolomic tools used in marine natural product drug discovery

Introduction: The marine environment is a very promising resource for natural product research, with many of these reaching the market as new drugs, especially in the field of cancer therapy as well as the drug discovery pipeline for new antimicrobials. Exploitation for bioactive marine compounds with unique structures and novel bioactivity such as the isoquinoline alkaloid; trabectedin, the polyether macrolide; halichondrin B, and the peptide; dolastatin 10, requires the use of analytical techniques, which can generate unbiased, quantitative, and qualitative data to benefit the biodiscovery process. Metabolomics has shown to bridge this understanding and facilitate the development of new potential drugs from marine sources and particularly their microbial symbionts.Areas covered: In this review, articles on applied secondary metabolomics ranging from 1990-2018 as well as to the last quarter of 2019 were probed to investigate the impact of metabolomics on drug discovery for new antibiotics and cancer treatment.Expert opinion: The current literature review highlighted the effectiveness of metabolomics in the study of targeting biologically active secondary metabolites from marine sources for optimized discovery of potential new natural products to be made accessible to a R&D pipeline.

An assessment of natural product discovery from marine (sensu strictu) and marine-derived fungi

The natural products community has been investigating secondary metabolites from marine fungi for several decades, but when one attempts to search for validated reports of new natural products from marine fungi, one encounters a literature saturated with reports from ‘marine-derived’ fungi. Of the 1000+ metabolites that have been characterized to date, only approximately 80 of these have been isolated from species from exclusively marine lineages. These metabolites are summarized here along with the lifestyle and habitats of their producing organisms. Furthermore, we address some of the reasons for the apparent disconnect between the stated objectives of discovering new chemistry from marine organisms and the apparent neglect of the truly exceptional obligate marine fungi. We also offer suggestions on how to reinvigorate enthusiasm for marine natural products discovery from fungi from exclusive marine lineages and highlight the need for critically assessing the role of apparently terrestrial fungi in the marine environment.

Unprecedented 17-residue peptaibiotics produced by marine-derived Trichoderma atroviride

In the course of investigations on marine-derived toxigenic fungi, five strains of Trichoderma atroviride were studied for their production of peptaibiotics. While these five strains were found to produce classical 19-residue peptaibols, three of them exhibited unusual peptidic sodium-adduct [M + 2 Na](2+) ion peaks at m/z between 824 and 854. The sequencing of these peptides led to two series of unprecedented 17-residue peptaibiotics based on the model Ac-XXX-Ala-Ala-XXX-XXX-Gln-Aib-Aib-Aib-Ala/Ser-Lxx-Aib-Pro-XXX-Aib-Lxx-[C(129) ]. The C-terminus of these new peptides was common to all of them, and its elemental formula C5 H9 N2 O2 was established by HR-MS. It could correspond to the cyclized form of N(δ) -hydroxyornithine which has already been observed at the C-terminus of various peptidic siderophores. The comparison of the sequences of 17- and 19-residue peptides showed similarities for positions 1-16. This observation seems to indicate a common biosynthesis pathway. Both new 17-residue peptaibiotics and 19-residue peptaibols exhibited weak in vitro cytotoxicities against KB cells.

Sequential determination of new peptaibols asperelines G-Z12 produced by marine-derived fungus Trichoderma asperellum using ultrahigh pressure liquid chromatography combined with electrospray-ionization tandem mass spectrometry

Thirty-eight short peptaibols in a microheterogeneous mixture derived from the fermentation broth of a marine-derived fungus Trichoderma asperellum were determined using ultrahigh pressure liquid chromatography in combination with electrospray-ionization tandem mass spectrometry (UHPLC-ESIMS/MS) techniques, including thirty-two new peptaibols namely asperelines G-Z13. The C-terminus bonded to proline (aspereline Z9) or hydroxyprolinol (aspereline Z12) is rarely found in nature. So far, it is the largest number of peptaibols to be detected at once on the basis of the selected ion monitoring (SIM) mode coupled to precursor scan techniques.

Aib and iva in the biosphere: neither rare nor necessarily extraterrestrial

Fourty-nine species and strains of filamentous fungi of the genera Acremonium, Bionectria, Clonostachys, Emericellopsis, Hypocrea/Trichoderma, Lecythophora, Monocillium, Nectriopsis, Niesslia, Tolypocladium, and Wardomyces, deposited with the culture collection of the Centraalbureau voor Schimmelcultures (CBS) in Utrecht, The Netherlands, were grown on nutrient agar plates. Organic extracts of mycelia were analyzed after acidic total hydrolysis and derivatization by GC/SIM-MS on Chirasil-L-Val for the presence of Aib (=alpha-aminoisobutyric acid, 2-methylalanine) and DL-Iva (=isovaline, 2-ethylalanine). In 37 of the hydrolysates, Aib was detected, and in several of them D-Iva or mixtures of D- and L-Iva. Non-proteinogenic Aib, in particular, is a highly specific marker for a distinctive group of fungal polypeptides named peptaibols or, comprehensively, peptaibiotics, i.e., peptides containing Aib and displaying (anti)biotic activities. The biotic synthesis of these amino acids by filamentous fungi contradicts the still widespread belief that alpha,alpha-dialkyl-alpha-amino acids do not or rarely occur in the biosphere and, if detected, are of extraterrestrial origin. The abundant production of peptaibiotics by cosmopolitan species of microfungi has also to be considered in the discussion on the occurrence of Aib and Iva in ancient and recent sediments. The detection of trace amounts of Aib in ice samples of Antarctica that are devoid of meteorites might also be related to the presence of Aib-producing microorganisms, being either indigenous psychrophiles, or being transported and localized by mechanisms related to bioaerosols and cryoconites. The presence of microfungi being capable of producing alpha,alpha-dialkyl alpha-amino acids in terrestrial samples, and possible contamination of extraterrestrial materials are pointed out to be of relevance for the reliable interpretation of cosmogeochemical data.