Total Synthesis of Homoseongomycin Enantiomers and Evaluation of Their Optical Rotation.

A total synthesis of each homoseongomycin enantiomer was accomplished in 17 total steps (longest linear sequence = 12 steps) and 10 chromatographic purifications. Several schemes were attempted to forge the key 5-membered ring, but only a Suzuki coupling-intramolecular Friedel-Crafts acylation sequence proved viable. Challenges encountered during the optical rotation characterization of the natural product left us with two important takeaways. First, highly colored compounds like homoseongomycin that absorb near/at the sodium d-line may require optical rotation measurements at other wavelengths. Second, high dilution of such compounds to obtain measurement at the sodium d-line could result in artificially large and incorrectly assigned specific rotations. To verify the optical rotation, electronic circular dichroism spectra were acquired for both homoseongomycin enantiomers and were transformed into optical rotary dispersions via the Kramers-Kronig transform. We note the wavelength dependency on rotation, and at the sodium d-line 589 nm, we reassign the optical rotation of L-homoseongomycin from (-) to (+).

Genome-based taxonomic analysis of the genus Pseudoalteromonas reveals heterotypic synonyms.

The Pseudoalteromonas genus comprises members that have been demonstrated to play significant ecological roles and produce enzymes, natural products, and activities that are beneficial to the environment and economy. A comprehensive evaluation of the genus revealed that the genomes of several Pseudoalteromonas species are highly similar to each other, exceeding species cutoff values. This evaluation involved determining and comparing the average nucleotide identity, in silico DNA-DNA hybridization, average amino acid identity, and the difference in G + C% between Pseudoalteromonas type strains with publicly available genomes. The genome of the Pseudoalteromonas elyakovii type strain was further assessed through additional sequencing and genomic comparisons to historical sequences. These findings suggest that six Pseudoalteromonas species, namely P. mariniglutinosa, P. donghaensis, P. maricaloris, P. elyakovii, P. profundi, and P. issachenkonii, should be reclassified as later heterotypic synonyms of the following validly published species: P. haloplanktis, P. lipolytica, P. flavipulchra, P. distincta, P. gelatinilytica, and P. tetraodonis. Furthermore, two names without valid standing, 'P. telluritireducens' and 'P. spiralis', should be associated with the validly published Pseudoalteromonas species P. agarivorans and P. tetraodonis, respectively.

Modulation of in Vitro SARS-CoV-2 Infection by Stephania tetrandra and Its Alkaloid Constituents.

Botanical natural products have been widely consumed for their purported usefulness against COVID-19. Here, six botanical species from multiple sources and 173 isolated natural product compounds were screened for blockade of wild-type (WT) SARS-CoV-2 infection in human 293T epithelial cells overexpressing ACE-2 and TMPRSS2 protease (293TAT). Antiviral activity was demonstrated by an extract from Stephania tetrandra. Extract fractionation, liquid chromatography-mass spectrometry (LC-MS), antiviral assays, and computational analyses revealed that the alkaloid fraction and purified alkaloids tetrandrine, fangchinoline, and cepharanthine inhibited WT SARS-CoV-2 infection. The alkaloids and alkaloid fraction also inhibited the delta variant of concern but not WT SARS-CoV-2 in VeroAT cells. Membrane permeability assays demonstrate that the alkaloids are biologically available, although fangchinoline showed lower permeability than tetrandrine. At high concentrations, the extract, alkaloid fractions, and pure alkaloids induced phospholipidosis in 293TAT cells and less so in VeroAT cells. Gene expression profiling during virus infection suggested that alkaloid fraction and tetrandrine displayed similar effects on cellular gene expression and pathways, while fangchinoline showed distinct effects on cells. Our study demonstrates a multifaceted approach to systematically investigate the diverse activities conferred by complex botanical mixtures, their cell-context specificity, and their pleiotropic effects on biological systems.

Nephroprotective plant species used in traditional Mayan Medicine for renal-associated diseases.

ETHNOPHARMACOLOGICAL RELEVANCE: The prevalence of kidney disease has increased rapidly in recent years and has emerged as one of the leading causes of mortality worldwide. Natural products have been suggested as valuable nephroprotective agents due to their multi-target and synergistic effects on modulating important proteins involved in kidney injury. There is a large number of plant species that have been used traditionally for kidney-related conditions in Mesoamerican medicine by different cultural groups that could provide a valuable source of nephroprotective therapeutic candidates and could lead to potential drug discovery. AIM OF REVIEW: This review aims to provide an overview of the currently known efficacy of plant species used traditionally in Mesoamerica by Mayan groups to treat kidney-related conditions and to analyze the phytochemical, pharmacological, molecular, toxicological, and clinical evidence to contribute to public health efforts and for directing future research. METHODS: Primary sources of plant use reports for traditional kidney-related disorders in Mesoamerica were searched systematically from library catalogs, theses, and scientific databases (PubMed, Google Scholar; and Science Direct), and were filtered according to usage frequency in Mayan groups and plant endemism. The database of traditional plants was further analyzed based on associations with published reports of the phytochemical, pharmacological, molecular, toxicological, and clinical evidence. RESULTS: The most reported kidney-related conditions used traditionally in Mayan medicine involve reducing renal damage (a cultural interpretation that considers an inflammatory or infectious condition), cleaning or purifying the blood and kidney, reducing kidney pain, and eliminating kidney stones. A total of 208 plants used for kidney-related problems by 10 Mayan groups were found, representing 143 native species, where only 42 have reported pharmacological activity against kidney damage, mainly approached by in vitro and in vivo models of chemical- or drug-induced nephrotoxicity, diabetes nephropathy, and renal injury produced by hypertension. Nephroprotective effects are mainly mediated by reducing oxidative stress, inflammatory response, fibrosis mechanisms, and apoptosis in the kidney. The most common nephroprotective compounds associated with traditional Mayan medicine were flavonoids, terpenoids, and phenolic acids. The most widely studied traditional plants in terms of pharmacological evidence, bioactive compounds, and mechanisms of action, are Annona muricata L., Carica papaya L., Ipomoea batatas (L.) Lam., Lantana camara L., Sechium edule (Jacq.) Sw., Tagetes erecta L., and Zea mays L. Most of the plant species with reported pharmacological activity against kidney damage were considered safe in toxicological studies. CONCLUSION: Available pharmacological reports suggest that several herbs used in traditional Mayan medicine for renal-associated diseases may have nephroprotective effects and consistent pharmacological evidence, nephroprotective compounds, and mechanisms of action in different models of kidney injury. However, more research is required to fully understand the potential of traditional Mayan medicine in drug discovery given the limited ethnobotanical studies and data available for most species with regards to identification on bioactive components, pharmacological mechanisms, and the scarce number of clinical studies.

Homoseongomycin, a compound isolated from marine actinomycete bacteria K3-1, is a potent inhibitor of encephalitic alphaviruses.

Marine microorganisms have been a resource for novel therapeutic drugs for decades. In addition to anticancer drugs, the drug acyclovir, derived from a marine sponge, is FDA-approved for the treatment of human herpes simplex virus-1 infections. Most alphaviruses that are infectious to terrestrial animals and humans, such as Venezuelan and eastern equine encephalitis viruses (VEEV and EEEV), lack efficient antiviral drugs and it is imperative to develop these remedies. To push the discovery and development of anti-alphavirus compounds forward, this study aimed to isolate and screen for potential antiviral compounds from cultured marine microbes originating from the marine environment. Compounds from marine microbes were of interest as they are prolific producers of bioactive compounds across the spectrum of human diseases and infections. Homoseongomycin, an actinobacteria isolated from a marine sponge displayed impressive activity against VEEV from a total of 76 marine bioactive products. The 50% effective concentration (EC50) for homoseongomycin was 8.6 µM for suppressing VEEV TC-83 luciferase reporter virus replication. Homoseongomycin was non-toxic up to 50 µM and partially rescued cells from VEEV induced cell death. Homoseongomycin exhibited highly efficient antiviral activity with a reduction of VEEV infectious titers by 8 log10 at 50 µM. It also inhibited EEEV replication with an EC50 of 1.2 µM. Mechanism of action studies suggest that homoseongomycin affects both early and late stages of the viral life cycle. Cells treated with 25 µM of homoseongomycin had a ~90% reduction in viral entry. In comparison, later stages showed a more robust reduction in infectious titers (6 log10) and VEEV extracellular viral RNA levels (4 log10), but a lesser impact on intracellular viral RNA levels (1.5 log10). In sum, this work demonstrates that homoseongomycin is a potential anti-VEEV and anti-EEEV compound due to its low cytotoxicity and potent antiviral activity.

Identification of Portimine B, a New Cell Permeable Spiroimine That Induces Apoptosis in Oral Squamous Cell Carcinoma.

Spiroimines are a class of compounds produced by marine dinoflagellates with a wide range of toxicity and therapeutic potential. The smallest of the cyclic imines, portimine, is far less toxic than other known members in several animal models. Portimine has also been shown to induce apoptosis and reduce the growth of a variety of cancer cell lines at low nanomolar concentrations. In an effort to discover new spiroimines, the current study undertook a metabolomic analysis of cultures of cyclic imine-producing dinoflagellates, and a new analog of portimine was discovered in which the five-membered cyclic ether is open. Further scrutiny with human oral cavity squamous cell carcinoma (OCSCC) cell lines revealed that the open ring congener was less potent than portimine A but could still lead to the accumulation of apoptotic gene transcripts, fragment genomic DNA, and reduce cancer cell proliferation in the range of 100-200 nM.

The biosynthesis of 15N-labeled microcystins and the comparative MS/MS fragmentation of natural abundance and their 15N-labeled congeners using LC-MS/MS.

The global need for accurate and sensitive quantitation of microcystins (MCs) persists as incidents of cyanobacterial harmful algal blooms continue to rise and recent research reveals an underestimation of the human health implications of these toxins. An optimal approach for their accurate quantitation relies on the availability of stable isotope-labeled MC standards for use in stable isotope dilution analysis (SIDA) strategies involving liquid chromatography tandem mass spectrometry (LC-MS/MS). Due to the dearth of isotopically labeled MCs, ten different 15N-enriched MCs were biosynthesized from producing cultures and fully characterized. This involved the comparative MS/MS fragmentation of natural abundance or unlabeled metabolites with their 15N-labeled congeners for improved confidence in product ion annotation. These results revealed a series of incorrect annotations described previously in the literature. In this manuscript, the biosynthesis of labeled microcystin is detailed, and their complete analytical characterization for prospective use in targeted SIDA applications, such as routine water testing is described.

Sulfated diesters of okadaic acid and DTX-1: Self-protective precursors of diarrhetic shellfish poisoning (DSP) toxins.

Many toxic secondary metabolites used for defense are also toxic to the producing organism. One important way to circumvent toxicity is to store the toxin as an inactive precursor. Several sulfated diesters of the diarrhetic shellfish poisoning (DSP) toxin okadaic acid have been reported from cultures of various dinoflagellate species belonging to the genus Prorocentrum. It has been proposed that these sulfated diesters are a means of toxin storage within the dinoflagellate cell, and that a putative enzyme mediated two-step hydrolysis of sulfated diesters such as DTX-4 and DTX-5 initially leads to the formation of diol esters and ultimately to the release of free okadaic acid. However, only one diol ester and no sulfated diesters of DTX-1, a closely related DSP toxin, have been isolated leading some to speculate that this toxin is not stored as a sulfated diester and is processed by some other means. DSP components in organic extracts of two large scale Prorocentrum lima laboratory cultures have been investigated. In addition to the usual suite of okadaic acid esters, as well as the free acids okadaic acid and DTX-1, a group of corresponding diol- and sulfated diesters of both okadaic acid and DTX-1 have now been isolated and structurally characterized, confirming that both okadaic acid and DTX-1 are initially formed in the dinoflagellate cell as the non-toxic sulfated diesters.

Microcystins and two new micropeptin cyanopeptides produced by unprecedented Microcystis aeruginosa blooms in North Carolina's Cape Fear River.

The Cape Fear River is the largest river system in North Carolina. It is heavily used as a source of drinking water for humans and livestock as well as a source of irrigation water for crops, and production water for industry. It also serves as a major fishery for both commercial and recreational use. In recent years, possibly related to increased eutrophication of the river, massive blooms of cyanobacteria, identified as Microcystis aeruginosa have been observed. Bloom samples collected in 2009 and 2012 were chemically analyzed to determine if they contained cyanobacterial toxins known as microcystins. Both blooms were found to produce microcystins in high yields. Microcystins are potent hepatotoxins that can be bio-accumulated in the food chain. Recent biological studies have also shown a host of other potentially harmful effects of low level microcystin exposure. Detailed chemical analysis of these blooms led us to discover that these blooms produce an additional family of cyanobacterial peptides know as the micropeptins, including two new members named micropeptins 1106 and 1120. The biological activities of these new molecules have not yet been determined, although protease activity has been well documented for this peptide group. These data indicate a need for thorough monitoring of toxin levels especially during bloom events in addition to additional biological testing of other cyanopeptides present in blooms.

Synthesis of phosphatidylinositol 3-kinase (PI3K) inhibitory analogues of the sponge meroterpenoid liphagal.

Analogues of the sponge meroterpenoid liphagal have been synthesized and evaluated for inhibition of PI3Kα and PI3Kγ as part of a program aimed at developing new isoform-selective PI3K inhibitors. One of the analogues, compound 24, with IC50 values of 66 nM against PI3Kα and 1840 nM against PI3Kγ, representing a 27-fold preference for PI3Kα, exhibited enhanced chemical stability and modestly enhanced potency and selectivity compared with the natural product liphagal.

Potent inhibitors of pro-inflammatory cytokine production produced by a marine-derived bacterium.

Cytokines produced through the antigen presenting cell (APC)-T-cell interaction play a key role in the activation of the allergic asthmatic response. Evaluating small molecules that inhibit the production of these pro-inflammatory proteins is therefore important for the discovery of novel chemical structures with potential antiasthma activity. We adapted a mouse splenocyte cytokine assay to screen a library of 2,500 marine microbial extracts for their ability to inhibit T(H)2 cytokine release and identified potent activity in a marine-derived strain CNQ431, identified as a Streptomyces species. Bioactivity guided fractionation of the organic extract of this strain led to the isolation of ten new 9-membered bis-lactones, splenocins A-J (1-10). The new compounds display potent biological activities, comparable to that of the corticosteroid dexamethasone, with IC(50) values from 2 to 50 nM in the splenocyte cytokine assay. This study provides the foundation for the optimization of these potent anti-inflammatory compounds for development in the treatment of asthma.

Thalassospiramides A and B, immunosuppressive peptides from the marine bacterium Thalassospira sp.

[structure: see text] Two new cyclic peptides, thalassospiramides A and B (1 and 2), were isolated from a new member of the marine alpha-proteobacterium Thalassospira. The thalassospiramides, the structures of which were assigned by combined spectral and chemical methods, bear unusual gamma-amino acids and show immunosuppressive activity in an interleukin-5 production inhibition assay (IC50 = 5 muM for thalassospiramide B).