Global Natural Products Social Research Articles

Mining Small Molecules from Teredinibacter turnerae Strains Isolated from Philippine Teredinidae.

Endosymbiotic relationship has played a significant role in the evolution of marine species, allowing for the development of biochemical machinery for the synthesis of diverse metabolites. In this work, we explore the chemical space of exogenous compounds from shipworm endosymbionts using LC-MS-based metabolomics. Priority T. turnerae strains (1022X.S.1B.7A, 991H.S.0A.06B, 1675L.S.0A.01) that displayed antimicrobial activity, isolated from shipworms collected from several sites in the Philippines were cultured, and fractionated extracts were subjected for profiling using ultrahigh-performance liquid chromatography with high-resolution mass spectrometry quadrupole time-of-flight mass analyzer (UHPLC-HRMS QTOF). T. turnerae T7901 was used as a reference microorganism for dereplication analysis. Tandem MS data were analyzed through the Global Natural Products Social (GNPS) molecular networking, which resulted to 93 clusters with more than two nodes, leading to four putatively annotated clusters: lipids, lysophosphatidylethanolamines, cyclic dipeptides, and rhamnolipids. Additional clusters were also annotated through molecular networking with cross-reference to previous publications. Tartrolon D cluster with analogues, turnercyclamycins A and B; teredinibactin A, dechloroteredinibactin, and two other possible teredinibactin analogues; and oxylipin (E)-11-oxooctadec-12-enoic acid were putatively identified as described. Molecular networking also revealed two additional metabolite clusters, annotated as lyso-ornithine lipids and polyethers. Manual fragmentation analysis corroborated the putative identification generated from GNPS. However, some of the clusters remained unclassified due to the limited structural information on marine natural products in the public database. The result of this study, nonetheless, showed the diversity in the chemical space occupied by shipworm endosymbionts. This study also affirms the use of bioinformatics, molecular networking, and fragmentation mechanisms analysis as tools for the dereplication of high-throughput data to aid the prioritization of strains for further analysis.

UHPLC-MS/MS-GNPS based phytochemical investigation of Dryopteris ramosa (Hope) C. Chr. and evaluation of cytotoxicity against liver and prostate cancer cell lines

Dryopteris ramosa (family; Dryopteridaceae) has been reported for its medicinal importance in cancer, gastrointestinal disorders, and infections. The present study aimed to investigate the detailed phytochemical profile of D. ramosa and its cytotoxic potential using various cancer cell lines. The phytochemical profile of D. ramosa methanolic extract and its fractions were established by employing UHPLC-MS/MS and Global Natural Product Social (GNPS) molecular networking. Moreover, the cytotoxic activity of extract and fractions was evaluated against human liver (HepG-2) and prostate cancer (PC-3) cells using MTT assay. Overall, 18 compounds including flavonoids, flavonoid O-glycosides, isoflavone di-C-glycoside, flavanol, flavanone, rotenoid, phloroglucinol derivative, coumarin derivative, benzofuranone, abietic acid, and phenolic acid were observed as the major phytochemical bioactive constituents in the extract and fractions of D. ramosa. In MTT assay, chloroform fraction showed highest anti-proliferative activity against liver cancer cells (IC50 = 53.49 μg/mL) followed by n-hexane fraction (IC50 = 55.36 μg/mL), D. ramosa extract (IC50 = 85.67 μg/mL) and ethyl acetate (IC50 = 125.00 μg/mL) fraction. However, n-hexane and chloroform fractions presented maximum cytotoxic effect against prostate cancer cells with respective IC50 values of 214.53 and 281.47 μg/mL. Moreover, all the tested samples showed negligible toxicity against non-cancer (BHK-21) cells. The results indicated that D. ramosa is rich in flavonoids, phloroglucinol derivative, and phenolic acids and showed positive results in cytotoxic studies, especially against liver cancer. Therefore, it can be considered safe for the development of anticancer drugs, especially against liver cancer.

Antihypertensive Activity in High Salt-Induced Hypertensive Rats and LC-MS/MS-Based Phytochemical Profiling of Melia azedarach L. (Meliaceae) Leaves.

Melia azedarach L. leaves have been traditionally used but not scientifically evaluated for antihypertensive activity. The focus of the present work was to carry out the detailed phytochemical profiling and antihypertensive potential of methanolic extract and subsequent fractions of this plant. The tandem mass spectrometry-based phytochemical profiling of M. azedarach extract (Ma.Cr) and fractions was determined in negative ionization mode while molecular networking was executed using the Global Natural Product Social (GNPS) molecular networking platform. This study resulted in the identification of 29 compounds including flavonoid O-glycosides, simple flavonoids, triterpenoidal saponins, and cardenolides as the major constituents. Ma.Cr at the concentration of 300 mg/kg resulted in a fall in blood pressure (BP), i.e., 81.44 ± 2.1 mmHg in high salt-induced hypertensive rats in vivo, in comparison to normotensive group, i.e., 65.36 ± 1.8 mmHg at the same dose. A decrease in blood pressure was observed in anaesthetized normotensive and hypertensive rats treated with extract and various fractions of M. azedarach. A reasonable activity was observed for all fractions except the aqueous fraction. The highest efficacy was shown by the ethyl acetate fraction, i.e., 77.06 ± 3.77 mmHg in normotensive and 88.96 ± 1.3 mmHg in hypertensive anaesthetized rats. Ma.Cr and fractions showed comparatively better efficacy towards hypertensive rats as compared to rats with normal blood pressure. Blood pressure-lowering effects did not change upon prior incubation with atropine. In vitro testing of Ma.Cr and polarity-based fractions resulted in L-NAME sensitive, endothelium-dependent vasodilator effects on aortic tissues. Pretreatment of aorta preparations with Ma.Cr and its fractions also blocked K+-induced precontractions indicating Ca2+ channel blocking activity comparable to verapamil. The extract and polarity-based fractions did not reveal a vasoconstrictor response in spontaneously beating isolated rat aorta. Ma.Cr and fractions when used in atrial preparations resulted in negative inotropic and chronotropic effects. These effects in atrial preparations did not change in the presence of atropine. These effects of extract and fractions explained the antihypertensive potential of M. azedarach and thus provided a scientific basis for its ethnopharmacological use in the treatment of hypertension. Among the constituents observed, flavonoids and flavonoid O-glycosides were previously reported for antihypertensive potential.

A complementary chromatographic strategy for integrated components characterization of Imperatae Rhizoma based on convergence and liquid chromatography combined with mass spectrometry and molecular network

The complexity of natural ingredients and the diversity of preparations are the major obstacles to the quality evaluation of traditional Chinese medicines (TCMs). A more comprehensive characterization of herbal compounds using different types of chromatographic separation techniques and covering a diverse polarity range can help evaluate the quality of TCMs. In this study, we first proposed a comprehensive method for characterizing compounds derived from Imperatae Rhizoma by combining the complementary strengths of UPCC-QTOF-MS (ultra-performance convergence chromatography coupled with quadrupole-time of flight mass spectrometry) with UPLC-QTOF-MS (ultra-performance liquid chromatography coupled with quadrupole-time of flight mass spectrometry). The method based on the UNIFI scientific platform significantly shortened the analysis time and enabled a more comprehensive characterization of known and unreported compounds. Meanwhile, a feature-based molecular network (FBMN) was established on the Global Natural Product Social (GNPS) to infer potential compounds by rapidly classifying and visualizing these components. A total of 62 compounds in Imperatae Rhizoma were jointly characterizedand classified into six types. In comparison, the UPCC-QTOF-MS technology individually characterized 17 components, including lactones, phenols, aldehydes, phenylpropanoids, and small polar organic acids. The UPLC-QTOF-MS technology characterized 16 compounds mainly phenylpropionic acids, flavonoid glycosides, and chromone glycosides. Furthermore, three types of characteristic compounds could be well aggregated into an FBMN approach. Five possible potential new compounds were detected through the supplementary identification of GNPS and the correlation analysis of vicinal known compounds. The strategy was first applied to Imperatae Rhizoma and facilitated the characterization of a large quantity of data to provide comprehensive chemical composition results. This approach can be easily extended to the study of the material basis of other herbs or preparations in order to improve the accuracy of herb quality evaluation.

TIMSCONVERT: a workflow to convert trapped ion mobility data to open data formats.

Advances in mass spectrometry have led to the development of mass spectrometers with ion mobility spectrometry capabilities and dual-source instrumentation; however, the current software ecosystem lacks interoperability with downstream data analysis using open-source software and pipelines. Here, we present TIMSCONVERT, a data conversion high-throughput workflow from timsTOF Pro/fleX mass spectrometer raw data files to mzML and imzML formats that incorporates ion mobility data while maintaining compatibility with data analysis tools. We showcase several examples using data acquired across different experiments and acquisition modalities on the timsTOF fleX MS. TIMSCONVERT and its documentation can be found at https://github.com/gtluu/timsconvert and is available as a standalone command-line interface tool for Windows and Linux, NextFlow workflow and online in the Global Natural Products Social (GNPS) platform. Supplementary data are available at Bioinformatics online.

Tandem high resolution mass spectrometry based phytochemical composition of Sauromatum guttatum tubers and its enzyme inhibitory potential with molecular docking

Sauromatum guttatum has been traditionally used in the treatment of snakebite and tumors in India, Pakistan, and China. However, it lacks detailed phytochemical composition like other members of the family Araceae. Therefore, the aim of the present study was to investigate the phytochemical composition of crude methanolic extract and subsequent fractions from S. guttatum tubers and to determine their enzyme inhibitory potentials. The phytochemical profile was studied through tandem high-resolution mass-based phytochemical analysis and Global Natural Product Social (GNPS) molecular networking. Similarly, crude extract and fractions were also investigated for enzyme inhibitory activity against urease and α-glucosidase. Twenty-six compounds were dereplicated belonging to flavone C-glycosides, flavone O-glycosides, phenolic acids, phenolic acid glycosides, and iridoid glycosides. The n-butanol fraction was particularly found rich in flavone di-C-glycosides including schaftoside, isoschaftoside, neoschaftoside, and vicenin-2. The n-butanol fraction exhibited the highest in vitro inhibition against urease and α-glucosidase with IC50 values of 113.7 µg/mL and 155.3 µg/mL, respectively. The results of enzyme inhibition potential were also supported by in silico molecular docking studies against the above-mentioned enzymes. This is the first report on the detailed phytochemical profile of S. guttatum tubers, and these results will contribute to the chemosystematic knowledge of the Araceae family. The results of this study also suggest that S. guttatum may find possible applications in the treatment of gastrointestinal disorders and diabetes.

Metabolomics of the wild mushroom Gymnopilus imperialis (Agaricomycetes, Basidiomycota) by UHPLC-HRMS/MS analysis and molecular network

Gymnopilus consists in a widely distributed genus of mushroom-forming fungi, especially in tropical regions of the world. Literature on Gymnopilus representatives reports the presence of oligoisoprenoids, and styrylpyrones. Considering the large number of secondary metabolites that basidiomycetes might contain, dereplication tools such as GNPS (Global Natural Products Social Molecular Networking), has become important in prospecting metabolites, saving time and work on isolation and characterization of natural products. Thus, this work identified the wild mushroom Gymnopilus imperialis and dereplicated their extracts with the aid of GNPS to annotate oligoisoprenoids. It was possible to annotate 24 oligoisoprenoids from methanol, dichloromethaneand ethyl acetate extracts of G. imperialis, 4 of them from GNPS spectral library match, and 20 from prediction based on molecular network. Moreover HRMS-ESI-(+) dereplication of the acetate extract annotated bisnoryangonin and hispidin. To the best of our knowledge, this is the first report on the annotation of a series of gymnopilins analogues based on GNPS molecular network. Our findings suggest that GNPS might be an effective, rapid, and open-source device to identify compounds and predict analogues.

Saliniquinone Derivatives, Saliniquinones G-I and Heraclemycin E, from the Marine Animal-Derived Nocardiopsis aegyptia HDN19-252.

Four new anthraquinone derivatives, namely saliniquinones G−I (1–3) and heraclemycin E (4), were obtained from the Antarctic marine-derived actinomycete Nocardiopsis aegyptia HDN19-252, guided by the Global Natural Products Social (GNPS) molecular networking platform. Their structures, including absolute configurations, were elucidated by extensive NMR, MS, and ECD analyses. Compounds 1 and 2 showed promising inhibitory activity against six tested bacterial strains, including methicillin-resistant coagulase-negative staphylococci (MRCNS), with MIC values ranging from 3.1 to 12.5 μM.

A conversation between hyphenated spectroscopic techniques and phytometabolites from medicinal plants.

Medicinal plant metabolomics has emerged as a goldmine for the natural product chemists. It provides a pool of bioactive phytoconstituents leading to accelerated novel discoveries and the elucidation of a variety of biosynthetic pathways. Further, it also acts as an innovative tool for herbal medicine's scientific validation and quality assurance. This review highlights different strategies and analytical techniques employed in the practice of metabolomics. Further, it also discusses several other applications and advantages of metabolomics in the area of natural product chemistry. Additional examples of integrating metabolomics with multivariate data analysis techniques for some Indian medicinal plants are also reviewed. Recent technical advances in mass spectrometry-based hyphenated techniques, nuclear magnetic resonance-based techniques, and comprehensive hyphenated technologies for phytometabolite profiling studies have also been reviewed. Mass Spectral Imaging (MSI) has been presented as a highly promising method for high precision in situ spatiotemporal monitoring of phytometabolites. We conclude by introducing GNPS (Global Natural Products Social Molecular Networking) as an emerging platform to make social networks of related molecules, to explore data and to annotate more metabolites, and expand the networks to novel "predictive" metabolites that can be validated.

Mass Spectrometry-Based Network Analysis Reveals New Insights Into the Chemodiversity of 28 Species in Aspergillus section Flavi.

Aspergillus section Flavi includes some of the most famous mycotoxin producing filamentous fungi known to mankind. In recent years a number of new species have been included in section Flavi, however these species have been much less studied from a chemical point of view. In this study, we explored one representative strain of a total of 28 fungal species in section Flavi by systematically evaluating the relationship between taxonomy and secondary metabolites with LC-MS/MS analysis for the first time and dereplication through an in-house database and the Global Natural Product Social Molecular Networking (GNPS) platform. This approach allowed rapid identification of two new cyclopiazonic acid producers (A. alliaceus and A. arachidicola) and two new tenuazonic acid producers (A. arachidicola and A. leporis). Moreover, for the first time we report species from section Flavi to produce fumifungin and sphingofungins B-D. Altogether, this study emphasizes that the chemical diversity of species in genus Aspergillus section Flavi is larger than previously recognized, and especially that understudied species are prolific producers of important mycotoxins such as fumi- and sphingofungins not previously reported from this section. Furthermore, our work demonstrates Global Natural Product Social (GNPS) Molecular Networking as a powerful tool for large-scale chemotaxonomic analysis of closely related species in filamentous fungi.

Structure-based molecular networking for the target discovery of novel germicidin derivatives from the sponge-associated streptomyces sp. 18A01.

Four new α-pyrone derivatives, named germicidins P-S (1-4) along with nine known analogues (5-13) were discovered from the sponge-associated Streptomyces sp. 18A01 guided by Global Natural Products Social (GNPS) molecular networking, the LC-DAD-MS profile, and hexokinase II (HK2) inhibitory activity. The structures of 1-13 were elucidated by analysis of their HRMS, optical rotation, and NMR spectroscopic data. The absolute configurations of germicidin P (1) and germicidin Q (2) were determined on the basis of comparisons of experimental and theoretically calculated ECD spectra. Bioactivities of the isolated compounds were assayed against human HK2. The bioassay results showed that compounds 1-4and 11-13 exhibited significant inhibitory activities against HK2, with IC50 values ranging from 5.1 to 11.0 μM. A molecular docking simulation demonstrated that these germicidins were docked in the inner active site tunnel of HK2. Interestingly, the amino residue Arg91 has a better binding affinity and efficacy than the amino residue Asn89 in the process of HK2 binding to the ligands, resulting in better hexokinase inhibitory activity. This result provided a valuable perspective for better understanding their HK2 inhibition activity.

Headspace Gas Chromatography/Mass Spectrometry Analysis Endorses Melaleuca Species as Abundant Source of Medicinal Eucalyptol and Its Proposed Anti-Obesity Activity

In the present study, the essential oils of the five Melaleuca species, ( Melaleuca bracteata, Melaleuca styphelioides, Melaleuca nesophila, Melaleuca leucadendra, and Melaleuca ericifolia ) were analyzed via headspace gas chromatography/ mass spectrometry (HS-GC/MS) analysis the unveiled considerable differences among the five Melaleuca accessions. Twelve volatile constituents were identified in the essential oils of Melaleuca accessions. Oxygenated monoterpene exemplified by eucalyptol was the main constituent in M. leucadendra and M. nesophila oils representing 97.62% and 95.08% of their aroma correspondingly followed by M. styphelioides (56.10 %), M. ericifolia (29%), and lastly M. bracteata (10.71%). A consecutive molecular network was constructed via the GNPS (Global Natural Products Social Molecular Networking) for the visual exploration of the volatile constituents among Melaleuca species. The constructed molecular network divulged eucalyptol (1,8 cineole) as the prevailing volatile, especially in M. leucadendra oil. Quantitative estimation of eucalyptol content in the studied species proved M. leucadendra oil as a potential source for its isolation with a content of 6031.8 µg/g dry weight. In addition, the effect of eucalyptol on the activity of digestive enzymes (α-amylase and pancreatic lipase) was assessed. Eucalyptol showed IC50 values of 75.3±2.1 and 64.6± 1.4 µg/ml for α-amylase and pancreatic lipase inhibition, compared with acarbose and orlistat 34.71±1.3 and 23.8± 0.82 µg/ml, respectively with significant difference of p Further target prediction studies for eucalyptol were applied and proposed the Cytochrome 450 19A1 aromatase enzyme as a possible target of eucalyptol that could be a potential alternative therapy in the management of obesity.

Novel Steroidal Saponins in Oat Identified by Molecular Networking Analysis and Their Levels in Commercial Oat Products.

Through the use of the Global Natural Product Social (GNPS) feature-based networking system, a series of newly identified steroidal saponins were discovered in oat. The structures of the three new major steroidal saponins, sativacosides A-C (1-3), were characterized by analyzing their high-resolution MS, 1D and 2D NMR spectra, and an additional eight new steroidal saponins were also tentatively identified (4-11) based on their tandem mass spectra and typical fragments. Using ultrahigh-performance liquid chromatography with tandem mass spectrometry techniques, a complete profile of the new sativacoside series was established, and the contents of sativacosides A-C were quantified in 18 different commercial oat products. The total levels of sativacosides A-C varied from 62.2 to 192.9 μg/g in these 18 products, in which oat bran (11 samples) and oatmeal (3 samples) had higher levels than cold oat cereal (4 samples).

Early Detection of Cyanobacterial Blooms and Associated Cyanotoxins using Fast Detection Strategy.

Fast detection of cyanobacteria and cyanotoxins is achieved using a Fast Detection Strategy (FDS). Only 24 h are needed to unravel the presence of cyanobacteria and related cyanotoxins in water samples and in an organic matrix, such as bivalve extracts. FDS combines remote/proximal sensing techniques with analytical/bioinformatics analyses. Sampling spots are chosen through multi-disciplinary, multi-scale, and multi-parametric monitoring in a three-dimensional physical space, including remote sensing. Microscopic observation and taxonomic analysis of the samples are performed in the laboratory setting, which allows for the identification of cyanobacterial species. Samples are then extracted with organic solvents and processed with LC-MS/MS. Data obtained by MS/MS are analyzed using a bioinformatic approach using the online platform Global Natural Products Social (GNPS) to create a network of molecules. These networks are analyzed to detect and identify toxins, comparing data of the fragmentation spectra obtained by mass spectrometry with the GNPS library. This allows for the detection of known toxins and unknown analogues that appear related in the same molecular network.

New from Old: Thorectandrin Alkaloids in a Southern Australian Marine Sponge, Thorectandra choanoides (CMB-01889)

Thorectandra choanoides (CMB-01889) was prioritized as a source of promising new chemistry from a library of 960 southern Australian marine sponge extracts, using a global natural products social (GNPS) molecular networking approach. The sponge was collected at a depth of 45 m. Chemical fractionation followed by detailed spectroscopic analysis led to the discovery of a new tryptophan-derived alkaloid, thorectandrin A (1), with the GNPS cluster revealing a halo of related alkaloids 1a–1n. In considering biosynthetic origins, we propose that Thorectandra choanoides (CMB-01889) produces four well-known alkaloids, 6-bromo-1′,8-dihydroaplysinopsin (2), 6-bromoaplysinopsin (3), aplysinopsin (4), and 1′,8-dihydroaplysinopsin (10), all of which are susceptible to processing by a putative indoleamine 2,3-dioxygenase-like (IDO) enzyme to 1a–1n. Where the 1′,8-dihydroalkaloids 2 and 10 are fully transformed to stable ring-opened thorectandrins 1 and 1a–1b, and 1h–1j, respectively, the conjugated precursors 3 and 4 are transformed to highly reactive Michael acceptors that during extraction and handling undergo complete transformation to artifacts 1c–1g, and 1k–1n, respectively. Knowledge of the susceptibility of aplysinopsins as substrates for IDOs, and the relative reactivity of Michael acceptor transformation products, informs our understanding of the pharmaceutical potential of this vintage marine pharmacophore. For example, the cancer tissue specificity of IDOs could be exploited for an immunotherapeutic response, with aplysinopsins transforming in situ to Michael acceptor thorectandrins, which covalently bind and inhibit the enzyme.

Neobulgarones Revisited: Anti and Syn Bianthrones from an Australian Mud Dauber Wasp Nest-Associated Fungus, Penicillium sp. CMB-MD22.

We report on the chemical analysis of a mud dauber wasp nest-associated fungus, Penicillium sp. CMB-MD22, leading to the discovery and structure elucidation of three known (1-3) and two new (4 and 5) anthrones, and a family of new and known bianthrones, neobulgarones 6-23. Detection and structure elucidation of 1-23 was supported by detailed spectroscopic analysis, as well as chemical (thermal) transformations, and global natural products social (GNPS) molecular networking. An empirical approach using HPLC retention times was effective at differentiating anti from syn bianthrone isomers, while a facile thermal equilibration was shown to favor anti over syn isomers. The neobulgarones 6-23 are natural products, and a crude extract rich in 6-23 exhibits selective antifungal activity against a co-isolated mud dauber wasp nest-associated fungus, suggestive of a possible ecological role as an antifungal chemical defense.

REDES MOLECULARES: UMA ANÁLISE SOBRE ANOTAÇÕES E DESCOBERTA DE NOVOS ATIVOS

MOLECULAR NETWORKS: AN ANALYSIS ON ANNOTATIONS AND DISCOVERY OF NEW ASSETS. To speed up the discovery of bioactive natural products (NP), chemists have sought advanced approaches in analytical and computational chemistry in attempt to organize and extract information from large data sets. In this sense, the molecular networks (MN) successfully organized enormous sets of mass spectrometry (MS) data together with samples metadata information in an intuitive visualization in the spectral similarity networks format. GNPS (Global Natural Products Social Molecular Networking), a free online platform for storing and processing MSn data, is a leading application of spectral matching with public databases aimed at the dereplication and discovery of new bioactive products through molecular networks. In this review, we address the concept of GNPS spectral similarity networks, as well as their complementary computational tools, benefits and limitations applied in NP studies associated with dereplication, chemical ecology, functional genetics and determination of biosynthetic pathways.

Auto-deconvolution and molecular networking of gas chromatography-mass spectrometry data.

We engineered a machine learning approach, MSHub, to enable auto-deconvolution of gas chromatography-mass spectrometry (GC-MS) data. We then designed workflows to enable the community to store, process, share, annotate, compare and perform molecular networking of GC-MS data within the Global Natural Product Social (GNPS) Molecular Networking analysis platform. MSHub/GNPS performs auto-deconvolution of compound fragmentation patterns via unsupervised non-negative matrix factorization and quantifies the reproducibility of fragmentation patterns across samples.

Monacycliones G-K and ent-Gephyromycin A, Angucycline Derivatives from the Marine-Derived Streptomyces sp. HDN15129.

Six new angucycline derivatives, named monacycliones G-K (1-5) and ent-gephyromycin A (6), as well as three known ones (7-9) were discovered from the marine sediment-derived actinomycete Streptomyces sp. HDN15129 guided by Global Natural Products Social (GNPS) molecular networking. Structures including absolute configurations were elucidated by extensive NMR, MS, and ECD analyses. Among them, monacyclione G (1) possesses a unique scaffold featuring a xanthone core linked to the aminodeoxysugar ossamine, and monacycliones H-J (2-4) are rare examples of natural angucyclines with an S-methyl group. Monacycliones I and J (3 and 4) showed cytotoxic activity against multiple human cancer cell lines, with IC50 values ranging from 3.5 to 10 μM.

Targeted Isolation of Rubrolides from the New Zealand Marine Tunicate Synoicum kuranui.

Global natural products social (GNPS) molecular networking is a useful tool to categorize chemical space within samples and streamline the discovery of new natural products. Here, we demonstrate its use in chemically profiling the extract of the marine tunicate Synoicum kuranui, comprised of many previously reported rubrolides, for new chemical entities. Within the rubrolide cluster, two masses that did not correspond to previously reported congeners were detected, and, following MS-guided fractionation, led to the isolation of new methylated rubrolides T (3) and (Z/E)–U (4). Both compounds showed strong growth inhibitory activity against the Gram-positive bacteria Bacillus subtilis, with minimum inhibitory concentration (MIC) values of 0.41 and 0.91 μM, respectively.