Indole is a significant structural moiety and functionalization of the C−H bond in indole‐containing molecules expands their chemical space, and modifies their properties and/or activities. Indole ...prenyltransferases (IPTs) catalyze the direct regiospecific installation of prenyl moieties on indole‐derived compounds. IPTs have shown relaxed substrate flexibility enabling them to be used as tools for indole functionalization. However, the mechanism by which certain IPTs target a specific carbon position is not fully understood. Herein, we use structure‐guided site‐directed mutagenesis, in vitro enzymatic reactions, kinetics and structural‐elucidation of analogs to verify the key catalytic residues that control the regiospecificity of all characterized regiospecific C6 IPTs. The presented results also demonstrate that substitution of PriB_His312 to Tyr leads to the synthesis of analogs prenylated at different positions than C6. This work contributes to understanding of how certain IPTs can access a challenging position in indole‐derived compounds.
The functionalization of indole‐derived compounds modifies their physicochemical properties and/or pharmacological activities. Activation of the indole C6 position is challenging. Yet, certain indole prenyltransferases (IPTs) catalyze this reaction efficiently, regiospecifically and under physiological conditions. Through enzyme engineering, in vitro enzymatic reactions and NMR experiments, guided by protein structure analyses, the mechanism was verified by which C6 IPTs catalyze their reactions.
Appalachian active coal fire sites were selected for the isolation of bacterial strains belonging to the class actinobacteria. A comparison of high-resolution electrospray ionization mass ...spectrometry (HRESIMS) and ultraviolet (UV) absorption profiles from isolate extracts to natural product databases suggested Streptomyces sp. RM-4-15 to produce unique metabolites. Four new pyranonaphthoquinones, frenolicins C–F (1–4), along with three known analogues, frenolicin (6), frenolicin B (7), and UCF76-A (8), were isolated from the fermentation of this strain. An additional new analogue, frenolicin G (5), along with two known compounds, deoxyfrenolicin (9) and UCF 13 (10), were isolated from the fermentation supplied with 18 mg/L of scandium chloride, the first example, to the best of our knowledge, wherein scandium chloride supplementation led to the confirmed production of new bacterial secondary metabolites. Structures 1–5 were elucidated on the basis of spectral analysis and chemical modification. While frenolicins are best known for their anticoccidial activity, the current study revealed compounds 6–9 to exhibit moderate cytotoxicity against the human lung carcinoma cell line (A549) and thereby extends the anticancer SAR for this privileged scaffold.
The structures and bioactivities of three unprecedented fused 5-hydroxyquinoxaline/alpha-keto acid amino acid metabolites (baraphenazines A–C, 1–3), two unique diastaphenazine-type metabolites ...(baraphenazines D and E, 4 and 5) and two new phenazinolin-type (baraphenazines F and G, 6 and 7) metabolites from the Himalayan isolate Streptomyces sp. PU-10A are reported. This study highlights the first reported bacterial strain capable of producing diastaphenazine-type, phenazinolin-type, and izumiphenazine A-type metabolites and presents a unique opportunity for the future biosynthetic interrogation of late-stage phenazine-based metabolite maturation.
Actinomadura melliaura ATCC 39691, a strain isolated from a soil sample collected in Bristol Cove, California, is a known producer of the disaccharide-substituted AT2433 indolocarbazoles (6–9). ...Reinvestigation of this strain using new media conditions led to >40-fold improvement in the production of previously reported AT2433 metabolites and the isolation and structure elucidation of the four new analogues, AT2433-A3, A4, A5, and B3 (1–4). The availability of this broader set of compounds enabled a subsequent small antibacterial/fungal/cancer SAR study that revealed disaccharyl substitution, N-6 methylation, and C-11 chlorination as key modulators of bioactivity. The slightly improved anticancer potency of the newly reported N-6-desmethyl 1 (compared to 6) contrasts extensive SAR of monoglycosylated rebeccamycin-type topoisomerase I inhibitors where N-6 alkylation has contributed to improved potency and ADME. Complete 2D NMR assignments for the known metabolite BMY-41219 (5) and 13C NMR spectroscopic data for the known analogue AT2433-B1 (7) are also provided for the first time.
Four cyclopentenone‐containing ansamycin polyketides (mccrearamycins A–D), and six new geldanamycins (Gdms B–G, including new linear and mycothiol conjugates), were characterized as metabolites of ...Streptomyces sp. AD‐23‐14 isolated from the Rock Creek underground coal mine acid drainage site. Biomimetic chemical conversion studies using both simple synthetic models and Gdm D confirmed that the mccrearamycin cyclopentenone derives from benzilic acid rearrangement of 19‐hydroxy Gdm, and thereby provides a new synthetic derivatization strategy and implicates a potential unique biocatalyst in mccrearamycin cyclopentenone formation. In addition to standard Hsp90α binding and cell line cytotoxicity assays, this study also highlights the first assessment of Hsp90α modulators in a new axolotl embryo tail regeneration (ETR) assay as a potential new whole animal assay for Hsp90 modulator discovery.
Mining for geldanamycins: Six new geldanamycins (Gdms) and four new ring‐contracted cyclopentenone macrolactams are reported as metabolites of an abandoned Kentucky coal mine associated microbe. A biosynthetic pathway via benzilic acid rearrangement is proposed and an axolotl embryo tail regeneration assay is utilized to assess the Hsp90 inhibitory activities of the metabolites.
The structures of 12 new “enantiomeric”-like abyssomicin metabolites (abyssomicins M–X) from Streptomyces sp. LC-6-2 are reported. Of this set, the abyssomicin W (11) contains an unprecedented ...8/6/6/6 tetracyclic core, while the bicyclic abyssomicin X (12) represents the first reported naturally occurring linear spirotetronate. Metabolite structures were determined based on spectroscopic data and X-ray crystallography, and Streptomyces sp. LC-6-2 genome sequencing also revealed the corresponding putative biosynthetic gene cluster.
We report the isolation and characterization of three new nybomycins (nybomycins B–D, 1–3) and six known compounds (nybomycin, 4; deoxynyboquinone, 5; α-rubromycin, 6; β-rubromycin, 7; γ-rubromycin, ...8; and 2α(1E,3E),4β-2-(1,3-pentadienyl)-4-piperidinol, 9) from the Rock Creek (McCreary County, KY) underground coal mine acid reclamation site isolate Streptomyces sp. AD-3-6. Nybomycin D (3) and deoxynyboquinone (5) displayed moderate (3) to potent (5) cancer cell line cytotoxicity and displayed weak to moderate anti-Gram-(+) bacterial activity, whereas rubromycins 6–8 displayed little to no cancer cell line cytotoxicity but moderate to potent anti-Gram-(+) bacterial and antifungal activity. Assessment of the impact of 3 or 5 cancer cell line treatment on 4E-BP1 phosphorylation, a predictive marker of ROS-mediated control of cap-dependent translation, also revealed deoxynyboquinone (5)-mediated downstream inhibition of 4E-BP1p. Evaluation of 1–9 in a recently established axolotl embryo tail regeneration assay also highlighted the prototypical telomerase inhibitor γ-rubromycin (8) as a new inhibitor of tail regeneration. Cumulatively, this work highlights an alternative nybomycin production strain, a small set of new nybomycin metabolites, and previously unknown functions of rubromycins (antifungal activity and inhibition of tail regeneration) and also provides a basis for revision of the previously proposed nybomycin biosynthetic pathway.
Four new Y-type actinomycin analogues named Y
-Y
(1-4) were isolated and characterized from the scale-up fermentation of the Streptomyces sp. strain Gö-GS12, as well as actinomycin Zp (5), which was, ...for the first time, isolated as a natural product. Structures of the new compounds were elucidated by the cumulative analyses of NMR spectroscopy and HRMS. The 4-hydroxythreonine on the β-ring of 1 uniquely undergoes both a rearrangement by a 2-fold acyl shift and an additional ring closure with the amino group of the phenoxazinone chromophore, and the α-rings of 4 and 5 contain a rare 5-methyl proline. Compounds 2-5 showed potent antibacterial activities against Gram-positive bacteria that correlated with cytotoxicity against representative human cell lines. The combination of a β-ring rearrangement and additional ring closure in 1 rendered this actinomycin significantly less potent relative to the nonrearranged comparator actinomycin Y
and other actinomycins.
Four new Y-type actinomycin analogues named Y6–Y9 (1–4) were isolated and characterized from the scale-up fermentation of the Streptomyces sp. strain Gö-GS12, as well as actinomycin Zp (5), which ...was, for the first time, isolated as a natural product. Structures of the new compounds were elucidated by the cumulative analyses of NMR spectroscopy and HRMS. The 4-hydroxythreonine on the β-ring of 1 uniquely undergoes both a rearrangement by a 2-fold acyl shift and an additional ring closure with the amino group of the phenoxazinone chromophore, and the α-rings of 4 and 5 contain a rare 5-methyl proline. Compounds 2–5 showed potent antibacterial activities against Gram-positive bacteria that correlated with cytotoxicity against representative human cell lines. The combination of a β-ring rearrangement and additional ring closure in 1 rendered this actinomycin significantly less potent relative to the nonrearranged comparator actinomycin Y5 and other actinomycins.
Venturicidin C (1), a new 20-membered macrolide along with the known venturicidins A (2) and B (3) were isolated from the crude extract of the Appalachian bacterial strain Streptomyces sp. TS-2-2. ...Additionally, nine other known compounds namely nocardamine, dehydroxynocardamine, desmethylenylnocardamine, ferrioxamine E, adenosine, riboflavin, cyclo(D)-trans-4-OH-Pro-(D)-Phe, cyclo(D)-Pro-(D)-Phe and N-(2-phenylethyl)-acetamide were also isolated and identified. The structure of the new macrolide 1 was elucidated by the cumulative analyses of NMR spectroscopy and HR-MS data. Complete NMR assignments for the known venturicidins A (2) and B (3) are also provided, for the first time, in this report. Venturicidins A-C did not inhibit the proliferation of A549 lung cancer cell line but all displayed potent antifungal activity.
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