Xiachang Wang

Frenolicins C–G, Pyranonaphthoquinones from Streptomyces sp. RM-4-15

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.

Herbimycins D–F, Ansamycin Analogues from Streptomyces sp. RM-7-15

Bacterial strains belonging to the class actinomycetes were isolated from the soil near a thermal vent of the Ruth Mullins coal fire (Appalachian Mountains of eastern Kentucky). High-resolution electrospray ionization mass spectrometry and ultraviolet absorption profiles of metabolites from one of the isolates (Streptomyces sp. RM-7-15) revealed the presence of a unique set of metabolites ultimately determined to be herbimycins D-F (1-3). In addition, herbimycin A (4), dihydroherbimycin A (TAN 420E) (7), and the structurally distinct antibiotic bicycylomycin were isolated from the crude extract of Streptomyces sp. RM-7-15. Herbimycins A and D-F (1-3) displayed comparable binding affinities to the Hsp90α. While the new analogues were found to be inactive in cancer cell cytotoxicity and antimicrobial assays, they may offer new insights in the context of nontoxic ansamycin-based Hsp90 inhibitors for the treatment of neurodegenerative disease.

A Diastereoselective Oxa-Pictet–Spengler-Based Strategy for (+)-Frenolicin B and epi-(+)-Frenolicin B Synthesis

An efficient diastereoselective oxa-Pictet-Spengler reaction strategy was developed to construct benzoisochroman diastereomers. The utility of the reaction was demonstrated in the context of both the total synthesis of naturally occurring pyranonaphthoquinones (+)-frenolicin B and epi-(+)-frenolicin B as well as a range of frenolicin precursor analogs. The method is versatile and offers exquisite stereocontrol and, as such, offers a synthetic advance for the synthesis of pyranonaphthoquinone analogs.

Mullinamides A and B, new cyclopeptides produced by the Ruth Mullins coal mine fire isolate Streptomyces sp. RM-27-46.

Two new cyclopeptides, mullinamides A [cyclo-(-L-Gly-L-Glu-L-Val-L-Ile-L-Pro-)] and B [cyclo-(-L-Glu-L-Met-L-Pro-)] were isolated from the crude extract of terrestrial Streptomyces sp. RM-27-46 along with the three known cyclopeptides surugamide A [cyclo-(-L-Ile-D-Ile-L-Lys-L-Ile-D-Phe-D-Leu-L-Ile-D-Ala-)], cyclo-(-L-Pro-L-Phe-) and cyclo-(-L-Pro-L-Leu-). The structures of the new compounds were elucidated by the cumulative analyses of NMR spectroscopy and HRMS. Although mullinamides A and B displayed no appreciable antimicrobial/fungal activity or cytotoxicity, this study highlights the first reported antibacterial activity of surugamide A.

Venturicidin C, a new 20-membered macrolide produced by Streptomyces sp. TS-2-2

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.

Cytotoxic Indolocarbazoles from Actinomadura melliaura ATCC 39691

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 (13)C NMR spectroscopic data for the known analogue AT2433-B1 (7) are also provided for the first time.

Ruthmycin, a New Tetracyclic Polyketide from Streptomyces sp. RM-4-15

The isolation and structural elucidation of a new tetracyclic polyketide (ruthmycin) from Streptomyces sp. RM-4-15, a bacteria isolated near thermal vents from the Ruth Mullins underground coal mine fire in eastern Kentucky, is reported. In comparison to the well-established frenolicin core scaffold, ruthmycin possesses an unprecedented signature C3 bridge and a corresponding fused six member ring. Preliminary in vitro antibacterial, anticancer, and antifungal assays revealed ruthmycin to display moderate antifungal activity.

The Native Production of the Sesquiterpene Isopterocarpolone by Streptomyces sp. RM-14-6

We report the production, isolation and structure elucidation of the sesquiterpene isopterocarpolone from an Appalachian isolate Streptomyces species RM-14-6. While isopterocarpolone was previously put forth as a putative plant metabolite, this study highlights the first native bacterial production of isopterocarpolone and the first full characterisation of isopterocarpolone using 1D and 2D NMR spectroscopy and HR-ESI mass spectrometry. Considering the biosynthesis of closely related metabolites (geosmin or 5-epiaristolochene), the structure of isopterocarpolone also suggests the potential participation of one or more unique enzymatic transformations. In this context, this work also sets the stage for the elucidation of potentially novel bacterial biosynthetic machinery.

Spoxazomicin D and Oxachelin C, Potent Neuroprotective Carboxamides from the Appalachian Coal Fire-Associated Isolate Streptomyces sp. RM-14-6

The isolation and structure elucidation of six new bacterial metabolites [spoxazomicin D (2), oxachelins B and C (4, 5), and carboxamides 6-8] and 11 previously reported bacterial metabolites (1, 3, 9-12a, and 14-18) from Streptomyces sp. RM-14-6 is reported. Structures were elucidated on the basis of comprehensive 1D and 2D NMR and mass spectrometry data analysis, along with direct comparison to synthetic standards for 2, 11, and 12a,b. Complete 2D NMR assignments for the known metabolites lenoremycin (9) and lenoremycin sodium salt (10) were also provided for the first time. Comparative analysis also provided the basis for structural revision of several previously reported putative aziridine-containing compounds [exemplified by madurastatins A1, B1, C1 (also known as MBJ-0034), and MBJ-0035] as phenol-dihydrooxazoles. Bioactivity analysis [including antibacterial, antifungal, cancer cell line cytotoxicity, unfolded protein response (UPR) modulation, and EtOH damage neuroprotection] revealed 2 and 5 as potent neuroprotectives and lenoremycin (9) and its sodium salt (10) as potent UPR modulators, highlighting new functions for phenol-oxazolines/salicylates and polyether pharmacophores.

Mccrearamycins A–D, Geldanamycin-Derived Cyclopentenone Macrolactams from an Eastern Kentucky Abandoned Coal Mine Microbe

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.