Covering: 1993-2014 (July)To alleviate the dereplication holdup, which is a major bottleneck in natural products discovery, scientists have been conducting their research efforts to add tools to their "bag of tricks" aiming to achieve faster, more accurate and efficient ways to accelerate the pace of the drug discovery process. Consequently dereplication has become a hot topic presenting a huge publication boom since 2012, blending multidisciplinary fields in new ways that provide important conceptual and/or methodological advances, opening up pioneering research prospects in this field.

Marine-derived actinomycete bacteria are emerging as a valuable resource for bioactive natural products encompassing a variety of unique structural classes.[1] In our hands, early detection of cell growth inhibitors using in vitro cytotoxicity assays against the colon carcinoma cancer cell line HCT-116, followed by extensive mechanism of action studies, has proven to be an effective approach. As such, the HCT-116 assay has been instrumental in the identification of potentially important anticancer agents. [2] In the course of our continued studies, Streptomyces strain CNR-698[3] was isolated from bottom sediments collected at a depth of 1618 meters in the Bahamas Islands in 2003. Cytotoxicity-guided (HCT-116) fractionation by C 18 flash chromatography and RP-HPLC of crude extract led to the isolation of ammosamides A (1) and B (2) as blue and red solids, respectively (3 and 4 mg L −1 ). Structure assignments for 1 and 2 proved to be particularly difficult due to their inherent insolubility (soluble only in dimethyl sulfoxide (DMSO)) and a lack of descriptive NMR signals, ultimately requiring the integration of NMR spectral analysis, mass spectrometry data, and single crystal X-ray diffraction studies. Inspection of the 1 H NMR spectrum of 1 in [D 6 ]DMSO revealed six singlets between δ=6.0 and 9.0 ppm and one methyl singlet at δ=4.03 ppm, while the 13 C NMR spectra revealed the presence of eleven sp 2 hybridized carbon atoms and a single sp 3 hybridized carbon atom at δ c =33.3 ppm ( Table 1). The addition of D 2 O (20 μL) to the sample in [D 6 ]DMSO resulted in the immediate disappearance of 1 H NMR signals at δ=7.16 (1H), 6.63 (1H), 6.89 ppm (2H) and the slower disappearance of singlets at δ=8.92 (1H), and 7.68 ppm (1H) (less than 10 min). The exchangeable protons at δ=7.16, 6.63 and 6.89 ppm were assigned as aromatic amines at C-6 and C-8 (based on HMBC correlations), while the slowly exchanging protons at δ=8.92 High-resolution (ESI NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript and 7.68 ppm were assigned to a primary amide on the basis of COSY and HMBC correlations. The only non-exchangeable hydrogen atoms were the methyl singlet resonance at δ=4.03 ppm and a one-proton singlet at δ=8.47 ppm. The 13 C NMR spectrum of 1 indicated the presence of two carbonyl groups (δ c =177.2 and 166.0 ppm), as well as two upfield sp 2 carbon atoms (δ c =103.1 and 110.5 ppm). HMBC correlations between the downfield carbonyl (δ c =177.2 ppm) and the proton methyl singlet at δ=4.03 ppm, we thought, defined an N-methyl amide, although a carbon chemical shift so far downfield would not be expected. In addition to correlations from the aromatic δ=8.47 ppm singlet, the only other HMBC correlations were from the exchangeable protons at δ=7.16/6.63 ppm to C-7 (δ c =103.1 ppm) and from δ=6.89 ppm to C-7 and C-8a (δ c =110.5 ppm).The spectral data for 1 suggested a highly unsaturated azaaromatic metabolite possessing three rings. However, the lack of definitive NMR assignments that could be used to link ...

A diverse collection of 60 marine-sediment-derived Actinobacteria representing 52 operational taxonomic units was screened by PCR for genes associated with secondary-metabolite biosynthesis. Three primer sets were employed to specifically target adenylation domains associated with nonribosomal peptide synthetases (NRPSs) and ketosynthase (KS) domains associated with type I modular, iterative, hybrid, and enediyne polyketide synthases (PKSs). In total, two-thirds of the strains yielded a sequence-verified PCR product for at least one of these biosynthetic types. Genes associated with enediyne biosynthesis were detected in only two genera, while 88% of the ketosynthase sequences shared greatest homology with modular PKSs. Positive strains included representatives of families not traditionally associated with secondary-metabolite production, including the Corynebacteriaceae, Gordoniaceae, Intrasporangiaceae, and Micrococcaceae. In four of five cases where phylogenetic analyses of KS sequences revealed close evolutionary relationships to genes associated with experimentally characterized biosynthetic pathways, secondary-metabolite production was accurately predicted. Sequence clustering patterns were used to provide an estimate of PKS pathway diversity and to assess the biosynthetic richness of individual strains. The detection of highly similar KS sequences in distantly related strains provided evidence of horizontal gene transfer, while control experiments designed to amplify KS sequences from Salinispora arenicola strain CNS-205, for which a genome sequence is available, led to the detection of 70% of the targeted PKS pathways. The results provide a bioinformatic assessment of secondarymetabolite biosynthetic potential that can be applied in the absence of fully assembled pathways or genome sequences. The rapid identification of strains that possess the greatest potential to produce new secondary metabolites along with those that produce known compounds can be used to improve the process of naturalproduct discovery by providing a method to prioritize strains for fermentation studies and chemical analysis.Microbial natural products represent the primary resource from which new medicines are derived, accounting for approximately half of the antibiotics discovered as of 2002 (6). Over the past several decades, however, drug discovery efforts have moved away from microbial products (29), in part due to a reduction in the ratio of new chemical entities discovered relative to the isolation of known metabolites (3) and the challenges associated with developing effective "dereplication" methods to improve the efficiency of the discovery process. More recently, the rise in drug-resistant pathogens has left many current antibiotics obsolete, while the limited success of alternative discovery strategies, such as combinatorial chemistry, have created a void in the pipeline of new drug leads (39). The response to this need includes renewed interest in a group of actinobacteria commonly called actinomycetes (defined here as ba...