Synthetic Studies Toward the Skyllamycins: Total Synthesis and Generation of Simplified Analogues

Herein, we report our synthetic studies toward the skyllamycins, a highly modified class of nonribosomal peptide natural products which contain a number of interesting structural features, including the extremely rare α-OH-glycine residue. Before embarking on the synthesis of the natural products, we prepared four structurally simpler analogues. Access to both the analogues and the natural products first required the synthesis of a number of nonproteinogenic amino acids, including three β-OH amino acids that were accessed from the convenient chiral precursor Garner’s aldehyde. Following the preparation of the suitably protected nonproteinogenic amino acids, the skyllamycin analogues were assembled using a solid-phase synthetic route followed by a final stage solution-phase cyclization reaction. To access the natural products (skyllamycins A–C) the synthetic route used for the analogues was modified. Specifically, linear peptide precursors containing a C-terminal amide were synthesized via solid-phase peptide synthesis. After cleavage from the resin the N-terminal serine residue was oxidatively cleaved to a glyoxyamide moiety. The target natural products, skyllamycins A–C, were successfully prepared via a final step cyclization with concomitant formation of the unusual α-OH-glycine residue. Purification and spectroscopic comparison to the authentic isolated material confirmed the identity of the synthetic natural products.AR

The Natural Products Atlas : an open access knowledge base for microbial natural products discovery

Despite rapid evolution in the area of microbial natural products chemistry, there is currently no open access database containing all microbially produced natural product structures. Lack of availability of these data is preventing the implementation of new technologies in natural products science. Specifically, development of new computational strategies for compound characterization and identification are being hampered by the lack of a comprehensive database of known compounds against which to compare experimental data. The creation of an open access, community-maintained database of microbial natural product structures would enable the development of new technologies in natural products discovery and improve the interoperability of existing natural products data resources. However, these data are spread unevenly throughout the historical scientific literature, including both journal articles and international patents. These documents have no standard format, are often not digitized as machine readable text, and are not publicly available. Further, none of these documents have associated structure files (e.g., MOL, InChI, or SMILES), instead containing images of structures. This makes extraction and formatting of relevant natural products data a formidable challenge. Using a combination of manual curation and automated data mining approaches we have created a database of microbial natural products (The Natural Products Atlas, www.npatlas.org) that includes 24 594 compounds and contains referenced data for structure, compound names, source organisms, isolation references, total syntheses, and instances of structural reassignment. This database is accompanied by an interactive web portal that permits searching by structure, substructure, and physical properties. The Web site also provides mechanisms for visualizing natural products chemical space and dashboards for displaying author and discovery timeline data. These interactive tools offer a powerful knowledge base for natural products discovery with a central interface for structure and property-based searching and presents new viewpoints on structural diversity in natural products. The Natural Products Atlas has been developed under FAIR principles (Findable, Accessible, Interoperable, and Reusable) and is integrated with other emerging natural product databases, including the Minimum Information About a Biosynthetic Gene Cluster (MIBiG) repository, and the Global Natural Products Social Molecular Networking (GNPS) platform. It is designed as a community-supported resource to provide a central repository for known natural product structures from microorganisms and is the first comprehensive, open access resource of this type. It is expected that the Natural Products Atlas will enable the development of new natural products discovery modalities and accelerate the process of structural characterization for complex natural products libraries

Total Synthesis of Skyllamycins

The skyllamycins are a family of highly functionalized non‐ribosomal cyclic depsipeptide natural products which contain the extremely rare α‐OH‐glycine functionality. Herein the first total synthesis of skyllamycins A–C is reported, together with the biofilm inhibitory activity of the natural products. Linear peptide precursors for each natural product were prepared through an efficient solid‐phase route incorporating a number of synthetic modified amino acids. A novel macrocyclization step between a C‐terminal amide and an N‐terminal glyoxylamide moiety served as a key transformation to install the unique α‐OH‐glycine unit and generate the natural products in the final step of the synthesis

Annotation of natural product compound families using molecular networking topology and structural similarity fingerprinting

Comparing experimental mass spectra to reference spectra can enable natural product identification, but these spectral libraries are often incomplete and not universally applicable. Here, the authors present SNAP-MS, a tool that allows assigning compound families without experimental or calculated reference spectra

Elucidation of unusual biosynthesis and DnaN-targeting mode of action of potent anti-tuberculosis antibiotics Mycoplanecins

DNA polymerase III sliding clamp (DnaN) was recently validated as a new antituberculosis target employing griselimycins. Three (2 S,4 R)−4-methylproline moieties of methylgriselimycin play significant roles in target binding and metabolic stability. Here, we identify the mycoplanecin biosynthetic gene cluster by genome mining using bait genes from the 4-methylproline pathway. We isolate and structurally elucidate four mycoplanecins comprising scarce homo-amino acids and 4-alkylprolines. Evaluating mycoplanecin E against Mycobacterium tuberculosis surprisingly reveals an excitingly low minimum inhibition concentration at 83 ng/mL, thus outcompeting griselimycin by approximately 24-fold. We show that mycoplanecins bind DnaN with nanomolar affinity and provide a co-crystal structure of mycoplanecin A-bound DnaN. Additionally, we reconstitute the biosyntheses of the unusual L-homoleucine, L-homonorleucine, and (2 S,4 R)−4-ethylproline building blocks by characterizing in vitro the full set of eight enzymes involved. The biosynthetic study, bioactivity evaluation, and drug target validation of mycoplanecins pave the way for their further development to tackle multidrug-resistant mycobacterial infections

Elucidation of unusual biosynthesis and DnaN-targeting mode of action of potent anti-tuberculosis antibiotics Mycoplanecins

Abstract DNA polymerase III sliding clamp (DnaN) was recently validated as a new anti-tuberculosis target employing griselimycins. Three (2 S,4 R)−4-methylproline moieties of methylgriselimycin play significant roles in target binding and metabolic stability. Here, we identify the mycoplanecin biosynthetic gene cluster by genome mining using bait genes from the 4-methylproline pathway. We isolate and structurally elucidate four mycoplanecins comprising scarce homo-amino acids and 4-alkylprolines. Evaluating mycoplanecin E against Mycobacterium tuberculosis surprisingly reveals an excitingly low minimum inhibition concentration at 83 ng/mL, thus outcompeting griselimycin by approximately 24-fold. We show that mycoplanecins bind DnaN with nanomolar affinity and provide a co-crystal structure of mycoplanecin A-bound DnaN. Additionally, we reconstitute the biosyntheses of the unusual l-homoleucine, l-homonorleucine, and (2 S,4 R)−4-ethylproline building blocks by characterizing in vitro the full set of eight enzymes involved. The biosynthetic study, bioactivity evaluation, and drug target validation of mycoplanecins pave the way for their further development to tackle multidrug-resistant mycobacterial infections

Lipopeptides from the Tropical Marine Cyanobacterium <i>Symploca</i> sp.

A collection of the tropical marine cyanobacterium <i>Symploca</i> sp., collected near Kimbe Bay, Papua New Guinea, previously yielded several new metabolites including kimbeamides A–C, kimbelactone A, and tasihalide C. Investigations into a more polar cytotoxic fraction yielded three new lipopeptides, tasiamides C–E (<b>1</b>–<b>3</b>). The planar structures were deduced by 2D NMR spectroscopy and tandem mass spectrometry, and their absolute configurations were determined by a combination of Marfey’s and chiral-phase GC-MS analysis. These new metabolites are similar to several previously isolated compounds, including tasiamide (<b>4</b>), grassystatins (<b>5</b>, <b>6</b>), and symplocin A, all of which were isolated from similar filamentous marine cyanobacteria

The Natural Products Atlas - data download

Download files from the Natural Products Atlas (npatlas.org). van Santen, J. A.; Jacob, G.; Leen Singh, A.; Aniebok, V.; Balunas, M. J.; Bunsko, D.; Carnevale Neto, F.; Castaño-Espriu, L.; Chang, C.; Clark, T. N.; Cleary Little, J. L.; Delgadillo, D. A.; Dorrestein, P. C.; Duncan, K. R.; Egan, J. M.; Galey, M. M.; Haeckl, F. P. J.; Hua, A.; Hughes, A. H.; Iskakova, D.; Khadilkar, A.; Lee, J.-H.; Lee, S.; LeGrow, N.; Liu, D. Y.; Macho, J. M.; McCaughey, C. S.; Medema, M. H.; Neupane, R. P.; O’Donnell, T. J.; Paula, J. S.; Sanchez, L. M.; Shaikh, A. F.; Soldatou, S.; Terlouw, B. R.; Tran, T. A.; Valentine, M.; van der Hooft, J. J. J.; Vo, D. A.; Wang, M.; Wilson, D.; Zink, K. E.; Linington, R. G.* "The Natural Products Atlas: An Open Access Knowledge Base for Microbial Natural Products Discovery”, ACS Central Science, 2019, 5, 11, 1824-1833. 10.1021/acscentsci.9b00806 Now includes ontological data from: NP Classifier - https://npclassifier.ucsd.edu/ ClassyFire - http://classyfire.wishartlab.com/ Including archived versions, extra data download types, and new MIBiG and GNPS IDs Includes dump of compounds deemed out of scope and removed from DB on May 19, 2021. The latest versions (v2021_08 onward) include the ontological data in the full JSON download

The Natural Products Atlas - data download

Download files from the Natural Products Atlas (npatlas.org). van Santen, J. A.; Jacob, G.; Leen Singh, A.; Aniebok, V.; Balunas, M. J.; Bunsko, D.; Carnevale Neto, F.; Castaño-Espriu, L.; Chang, C.; Clark, T. N.; Cleary Little, J. L.; Delgadillo, D. A.; Dorrestein, P. C.; Duncan, K. R.; Egan, J. M.; Galey, M. M.; Haeckl, F. P. J.; Hua, A.; Hughes, A. H.; Iskakova, D.; Khadilkar, A.; Lee, J.-H.; Lee, S.; LeGrow, N.; Liu, D. Y.; Macho, J. M.; McCaughey, C. S.; Medema, M. H.; Neupane, R. P.; O’Donnell, T. J.; Paula, J. S.; Sanchez, L. M.; Shaikh, A. F.; Soldatou, S.; Terlouw, B. R.; Tran, T. A.; Valentine, M.; van der Hooft, J. J. J.; Vo, D. A.; Wang, M.; Wilson, D.; Zink, K. E.; Linington, R. G.* "The Natural Products Atlas: An Open Access Knowledge Base for Microbial Natural Products Discovery”, ACS Central Science, 2019, 5, 11, 1824-1833. 10.1021/acscentsci.9b00806 Now includes ontological data from: NP Classifier - https://npclassifier.ucsd.edu/ ClassyFire - http://classyfire.wishartlab.com/ Including archived versions, extra data download types, and new MIBiG and GNPS IDs Includes dump of compounds deemed out of scope and removed from DB on May 19, 2021. The latest versions (v2021_08 onward) include the ontological data in the full JSON download