Re-evaluation of the Fijianolide/Laulimalide Chemotype Suggests an Alternate Mechanism of Action for C-15/C-20 Analogs.

Herein, we report on naturally derived microtubule stabilizers with activity against triple negative breast cancer (TNBC) cell lines, including paclitaxel, fijianolide B/laulimalide (3), fijianolide B di-acetate (4), and two new semisynthetic analogs of 3, which include fijianolide J (5) and fijianolide L (6). Similar to paclitaxel, compound 3 demonstrated classic microtubule stabilizing activity with potent (GI50 = 0.7-17 nM) antiproliferative efficacy among the five molecularly distinct TNBC cell lines. Alternatively, compounds 5 or 6, generated from oxidation of C-20 or C-15 and C-20 respectively, resulted in a unique profile with reduced potency (GI50 = 4-9 µM), but improved efficacy in some lines, suggesting a distinct mechanism of action. The C-15, C-20 di-acetate, and dioxo modifications on 4 and 6 resulted in compounds devoid of classic microtubule stabilizing activity in biochemical assays. While 4 also had no detectable effect on cellular microtubules, 6 promoted a reorganization of the cytoskeleton resulting in an accumulation of microtubules at the cell periphery. Compound 5, with a single C-20 oxo substitution, displayed a mixed phenotype, sharing properties of 3 and 6. These results demonstrate the importance of the C-15/C-20 chiral centers, which appear to be required for the potent microtubule stabilizing activity of this chemotype and that oxidation of these sites promotes unanticipated cytoskeletal alterations that are distinct from classic microtubule stabilization, likely through a distinct mechanism of action.

Reinvestigation of Mycothiazole Reveals the Penta-2,4-dien-1-ol Residue Imparts Picomolar Potency and 8S Configuration.

Reinvestigation of mycothiazole (1) revealed picomolar potency (IC50 = 0.00016, 0.00027, 0.00035 µM) against pancreatic, (PANC-1), liver (HepG2), and colon (HCT-116) tumor cell lines. Reevaluation of 1 provided [α]D data indicating Vanuatu specimens of C. mycofijiensis contain the 8S enantiomer of 1 and not the 8R configuration previously reported. Semisynthesis provided 8-O-acetylmycothiazole (2), 8-oxomycothiazole (8), mycothiazole nitrosobenzene derivatives (MND1, MND2: 9a, 9b), and MND3 (10) with IC50 = 0.00129, >1.0, >1.0, >1.0, >1.0 µM, respectively, against PANC-1 cell lines. These results highlight the significance of the penta-2,4-dien-1-ol residue as a key structural feature of 1 required for its cytotoxicty against tumor cell lines.

The value of universally available raw NMR data for transparency, reproducibility, and integrity in natural product research.

Covering: up to 2018With contributions from the global natural product (NP) research community, and continuing the Raw Data Initiative, this review collects a comprehensive demonstration of the immense scientific value of disseminating raw nuclear magnetic resonance (NMR) data, independently of, and in parallel with, classical publishing outlets. A comprehensive compilation of historic to present-day cases as well as contemporary and future applications show that addressing the urgent need for a repository of publicly accessible raw NMR data has the potential to transform natural products (NPs) and associated fields of chemical and biomedical research. The call for advancing open sharing mechanisms for raw data is intended to enhance the transparency of experimental protocols, augment the reproducibility of reported outcomes, including biological studies, become a regular component of responsible research, and thereby enrich the integrity of NP research and related fields.

Correction: The value of universally available raw NMR data for transparency, reproducibility, and integrity in natural product research.

Correction for 'The value of universally available raw NMR data for transparency, reproducibility, and integrity in natural product research' by James B. McAlpine et al., Nat. Prod. Rep., 2018, DOI: .

Application of the DP4 Probability Method to Flexible Cyclic Peptides with Multiple Independent Stereocenters: The True Structure of Cyclocinamide A.

A DP4 protocol has been successfully utilized to establish the true structure of the natural product cyclocinamide A, a flexible cyclic peptide with four isolated stereocenters. Benchmarking the necessary level of theory required to successfully predict the NMR spectra of three previously synthesized isomers of cyclocinamide A led to the prediction of the natural stereochemistry as 4 S, 7 R, 11 R, 14 S, which has been confirmed by total synthesis.

Evaluating Nitrogen-Containing Biosynthetic Products Produced by Saltwater Culturing of Several California Littoral Zone Gram-Negative Bacteria.

The biosynthetic potential of marine-sediment-derived Gram-negative bacteria is poorly understood. Sampling of California near-shore marine environments afforded isolation of numerous Gram-negative bacteria in the Proteobacteria and Bacteriodetes phyla, which were grown in the laboratory to provide extracts whose metabolites were identified by comparative analyses of LC-mass spectrometry and MSn data. Overall, we developed an assemblage of seven bacterial strains grown in five different media types designed to coax out unique secondary metabolite production as a function of varying culture conditions. The changes in metabolite production patterns were tracked using the GNPS MS2 fragmentation pattern analysis tool. A variety of nitrogen-rich metabolites were visualized from the different strains grown in different media, and strikingly, all of the strains examined produced the same new, proton-atom-deficient compound, 1-methyl-4-methylthio-ß-carboline (1), C13H12N2S. Scale-up liquid culture of Achromobacter spanius (order: Burkholderiales; class: Betaproteobacteria) provided material for the final structure elucidation. The methods successfully combined in this work should stimulate future studies of molecules from marine-derived Gram-negative bacteria.