Asymmetric Synthesis of Four Stereoisomers of 2,2-Dimethyl-3-hydroxy-4-(1'-angeloyloxy)-6-acetylchromane from Ageratina grandifolia and Plausible Absolute Stereochemistry of the Natural Product.

2,2-Dimethyl-3-hydroxy-4-(1'-angeloyloxy)-6-acetylchromane is a natural product isolated from Ageratina grandifolia that exhibits inhibitory activity against yeast α-glucosidase. Initially, its structure was proposed to be 4-hydroxy-3-((S)-1'-angeloyloxy-(R)-2',3'-epoxy-3'-methyl)butylacetophenone with an epoxide, but the structure was later revised to 2,2-dimethyl-3R-hydroxy-4S-(1-angeloyloxy)-6-acetylchromane. In this study, we present a total synthesis of 2,2-dimethyl-3-hydroxy-4-(1'-angeloyloxy)-6-acetylchromane from A. gradifolia and its stereoisomers. The key features of their synthesis include Sharpless asymmetric dihydroxylation of a readily available benzopyran substrate and subsequent Mitsunobu or Steglich reaction to provide both cis- and trans-isomers with chiral control. The absolute stereochemistry of the natural product was determined to be 2,2-dimethyl-3S-hydroxy-4R-(1'-angeloyloxy)-6-acetylchromane based on optical rotations of the synthesized compounds. The absolute configuration of the synthesized stereoisomers was confirmed by Mosher ester analysis. In addition, we provided ECD spectra for the four stereoisomers, which will allow verification of the absolute configuration of the natural product. Synthesis of all four stereoisomers of 2,2-dimethyl-3-hydroxy-4-(1'-angeloyloxy)-6-acetylchromane would facilitate the exploration of their potential biomedical applications.

Collinsella aerofaciens Produces a pH-Responsive Lipid Immunogen.

Some members of the human gut microbiota profoundly influence their host's physiology, health, and therapeutic responses, but the responsible molecules and mechanisms are largely unknown. As part of a project to identify immunomodulators produced by gut microbes, we analyzed the metabolome of Collinsella aerofaciens, an actinomycete that figures prominently in numerous association studies. The associations are typically positive correlations of C. aerofaciens with pro-inflammatory responses and undesirable outcomes, but an association with favorable responses to PD-1/PD-L1 cancer immunotherapy is a notable exception. A phenotypic assay-guided screen using dendritic cells (mBMDCs) and cytokine readouts identified the active compound, which was structurally characterized as a lysoglycoglycerolipid with an acetal-bearing ß-galactofuranose head group (CaLGL-1, 1). The structural assignment was confirmed through total synthesis. Assays with tlr2-/-, tlr4-/-, and wt mBMDCs revealed TLR2-dependent signaling. CaLGL-1 is produced by a conversion of a bacterially biosynthesized plasmalogen (CaPlsM, 3) to CaLGL-1 (1) in a low-pH environment.

Clathrin light chain-conjugated drug delivery for cancer.

Targeted drug delivery systems hold the remarkable potential to improve the therapeutic index of anticancer medications markedly. Here, we report a targeted delivery platform for cancer treatment using clathrin light chain (CLC)-conjugated drugs. We conjugated CLC to paclitaxel (PTX) through a glutaric anhydride at high efficiency. Labeled CLCs localized to 4T1 tumors implanted in mice, and conjugation of PTX to CLC enhanced its delivery to these tumors. Treatment of three different mouse models of cancer-melanoma, breast cancer, and lung cancer-with CLC-PTX resulted in significant growth inhibition of both the primary tumor and metastatic lesions, as compared to treatment with free PTX. CLC-PTX treatment caused a marked increase in apoptosis of tumor cells and reduction of tumor angiogenesis. Our data suggested HSP70 as a binding partner for CLC. Our study demonstrates that CLC-based drug-conjugates constitute a novel drug delivery platform that can augment the effects of chemotherapeutics in treating a variety of cancers. Moreover, conjugation of therapeutics with CLC may be used as means by which drugs are delivered specifically to primary tumors and metastatic lesions, thereby prolonging the survival of cancer patients.

Synthesis and Structure Revision of Naturally Occurring Homoisoflavane (+)-Dracaeconolide B.

Dracaeconolide B (1), a naturally occurring homoisoflavane, was isolated from the red resin of Dracaena cochinchinensis. Efforts have been made to elucidate the exact structure of compound 1 since it was confirmed that dracaeconolide B did not contain a 7-hydroxy-5,8-dimethoxy moiety. The structure of dracaeconolide B was revised by synthesis of three homoisoflavanes containing a 5,6,7-trioxygenated moiety each and analysis by NMR spectroscopy. The revised structure of dracaeconolide B was proposed as 3-(4-hydroxybenzyl)-7-hydroxy-5,6-dimethoxychromane. Noyori's Ru-catalyzed asymmetric transfer hydrogenation was used to synthesize (+)-dracaeconolide B. The absolute configuration of the compound was revised to S based on the results obtained by the electronic circular dichroism calculation. We examined the antiangiogenic activity of (S)- and (R)-dracaeconolide B and of synthetic 5,6,7- and 5,7,8-trioxygenated homoisoflavanes. The results can potentially help in the synthesis of related natural products and support drug discovery to treat neovascular eye diseases.

Actinoflavosides B-D, Flavonoid Type Glycosides from Tidal Mudflat-Derived Actinomyces.

Three new secondary metabolites, actinoflavosides B-D (1-3), were discovered in the culture broth of two actinomycete strains (JML48 and JMS33) that were isolated from tidal mudflat sediment in Muan, Republic of Korea. The planar structures of the actinoflavosides were elucidated by MS, UV, and NMR analyses. The stereochemistry of an aminosugar, 2,3,6-trideoxy-3-amino-ribopyranoside in the actinoflavosides was determined by J-based configuration analysis using values obtained from DQF-COSY experiments and modified Mosher's method. Actinoflavosides B-D (1-3) displayed antibacterial activity against Pseudomonas aeruginosa, and actinoflavoside D (3) significantly increased IL-2 production in mouse splenocytes.

Akkermansia muciniphila phospholipid induces homeostatic immune responses.

Multiple studies have established associations between human gut bacteria and host physiology, but determining the molecular mechanisms underlying these associations has been challenging1-3. Akkermansia muciniphila has been robustly associated with positive systemic effects on host metabolism, favourable outcomes to checkpoint blockade in cancer immunotherapy and homeostatic immunity4-7. Here we report the identification of a lipid from A. muciniphila's cell membrane that recapitulates the immunomodulatory activity of A. muciniphila in cell-based assays8. The isolated immunogen, a diacyl phosphatidylethanolamine with two branched chains (a15:0-i15:0 PE), was characterized through both spectroscopic analysis and chemical synthesis. The immunogenic activity of a15:0-i15:0 PE has a highly restricted structure-activity relationship, and its immune signalling requires an unexpected toll-like receptor TLR2-TLR1 heterodimer9,10. Certain features of the phospholipid's activity are worth noting: it is significantly less potent than known natural and synthetic TLR2 agonists; it preferentially induces some inflammatory cytokines but not others; and, at low doses (1% of EC50) it resets activation thresholds and responses for immune signalling. Identifying both the molecule and an equipotent synthetic analogue, its non-canonical TLR2-TLR1 signalling pathway, its immunomodulatory selectivity and its low-dose immunoregulatory effects provide a molecular mechanism for a model of A. muciniphila's ability to set immunological tone and its varied roles in health and disease.

Taeanamides A and B, Nonribosomal Lipo-Decapeptides Isolated from an Intertidal-Mudflat-Derived Streptomyces sp.

Two new lipo-decapeptides, namely taeanamides A and B (1 and 2), were discovered from the Gram-positive bacterium Streptomyces sp. AMD43, which was isolated from a mudflat sample from Anmyeondo, Korea. The exact molecular masses of 1 and 2 were revealed by high-resolution mass spectrometry, and the planar structures of 1 and 2 were elucidated using NMR spectroscopy. The absolute configurations of 1 and 2 were determined using a combined analysis of 1H-1H coupling constants and ROESY correlations, the advanced Marfey's method, and bioinformatics. The putative nonribosomal peptide synthetase pathway for the taeanamides was identified by analyzing the full genome sequence data of Streptomyces sp. AMD43. We also found that taeanamide A exhibited mild anti-tuberculosis bioactivity, whereas taeanamide B showed significant bioactivity against several cancer cell lines.

Cyclodimerization of Mohangamide A by Thioesterase Domain Is Directed by Substrates.

Mohangamide A is a pseudo-dimeric nonribosomal peptide biosynthesized along with its monomer, WS9326A, and is expected to be formed by the head-to-tail cyclodimerization of linear WS9326A and another identical peptide chain with a different acyl side chain. In vitro experiments with the N-acetylcysteamine thioesters of the corresponding monomeric intermediates and thioesterase domains of Streptomyces sp. SNM55 and S. calvus showed that this cyclodimerization reaction is directed by the substrate structures and occurs only with both linear intermediates.

Lyme Disease, Borrelia burgdorferi, and Lipid Immunogens.

The human immune system detects potentially pathogenic microbes with receptors that respond to microbial metabolites. While the overall immune signaling pathway is known in considerable detail, the initial molecular signals, the microbially produced immunogens, for important diseases like Lyme disease (LD) are often not well-defined. The immunogens for LD are produced by the spirochete Borrelia burgdorferi, and a galactoglycerolipid (1) has been identified as a key trigger for the inflammatory immune response that characterizes LD. This report corrects the original structural assignment of 1 to 3, a change of an α-galactopyranose to an α-galactofuranose headgroup. The seemingly small change has important implications for the diagnosis, prevention, and treatment of LD.

Targeted Degradation of the Oncogenic Phosphatase SHP2.

SHP2 is a protein tyrosine phosphatase that plays a critical role in the full activation of the Ras-MAPK pathway upon stimulation of receptor tyrosine kinases, which are frequently amplified or mutationally activated in human cancer. In addition, activating mutations in SHP2 result in developmental disorders and hematologic malignancies. Several allosteric inhibitors have been developed for SHP2 and are currently in clinical trials. Here, we report the development and evaluation of a SHP2 PROTAC created by conjugating RMC-4550 with pomalidomide using a PEG linker. This molecule is highly selective for SHP2, induces degradation of SHP2 in leukemic cells at submicromolar concentrations, inhibits MAPK signaling, and suppresses cancer cell growth. SHP2 PROTACs serve as an alternative strategy for targeting ERK-dependent cancers and are useful tools alongside allosteric inhibitors for dissecting the mechanisms by which SHP2 exerts its oncogenic activity.

A bacterial bile acid metabolite modulates Treg activity through the nuclear hormone receptor NR4A1.

Bile acids act as signaling molecules that regulate immune homeostasis, including the differentiation of CD4+ T cells into distinct T cell subsets. The bile acid metabolite isoallolithocholic acid (isoalloLCA) enhances the differentiation of anti-inflammatory regulatory T cells (Treg cells) by facilitating the formation of a permissive chromatin structure in the promoter region of the transcription factor forkhead box P3 (Foxp3). Here, we identify gut bacteria that synthesize isoalloLCA from 3-oxolithocholic acid and uncover a gene cluster responsible for the conversion in members of the abundant human gut bacterial phylum Bacteroidetes. We also show that the nuclear hormone receptor NR4A1 is required for the effect of isoalloLCA on Treg cells. Moreover, the levels of isoalloLCA and its biosynthetic genes are significantly reduced in patients with inflammatory bowel diseases, suggesting that isoalloLCA and its bacterial producers may play a critical role in maintaining immune homeostasis in humans.

Unprecedented Noncanonical Features of the Nonlinear Nonribosomal Peptide Synthetase Assembly Line for WS9326A Biosynthesis.

Systematic inactivation of nonribosomal peptide synthetase (NRPS) domains and translocation of the thioesterase (TE) domain revealed several unprecedented nonlinear NRPS assembly processes during the biosynthesis of the cyclodepsipeptide WS9326A in Streptomyces sp. SNM55. First, two sets of type ΙΙ TE (TEΙΙ)-like enzymes mediate the shuttling of activated amino acids between two sets of stand-alone adenylation (A)-thiolation (T) didomain modules and an "A-less" condensation (C)-T module with distinctive specificities and flexibilities. This was confirmed by the elucidation of the affinities of the A-T didomains for the TEΙΙs and its structure. Second, the C-T didomain module operates iteratively and independently from other modules in the same protein to catalyze two chain elongation cycles. Third, this biosynthetic pathway includes the first example of module skipping, where the interpolated C and T domains are required for chain transfer.

Bacterial diketopiperazines stimulate diatom growth and lipid accumulation.

Diatoms are photosynthetic microalgae that fix a significant fraction of the world's carbon. Because of their photosynthetic efficiency and high-lipid content, diatoms are priority candidates for biofuel production. Here, we report that sporulating Bacillus thuringiensis and other members of the Bacillus cereus group, when in co-culture with the marine diatom Phaeodactylum tricornutum, significantly increase diatom cell count. Bioassay-guided purification of the mother cell lysate of B. thuringiensis led to the identification of two diketopiperazines (DKPs) that stimulate both P. tricornutum growth and increase its lipid content. These findings may be exploited to enhance P. tricornutum growth and microalgae-based biofuel production. As increasing numbers of DKPs are isolated from marine microbes, the work gives potential clues to bacterial-produced growth factors for marine microalgae.

Chemical Exchanges between Multilateral Symbionts.

Herein is a report on the molecular exchange occurring between multilateral symbiosis partners-a tit-for-tat exchange that led to the characterization of two new metabolites, conocandin B (fungal-derived) and dentigerumycin F (bacterial-derived). The structures were determined by NMR, mass spectrometry, genomic analysis, and chemical derivatizations. Conocandin B exhibits antimicrobial activity against both the bacterial symbionts of fungus-growing ant and human pathogenic strains by selectively inhibiting FabH, thus disrupting fatty acid biosynthesis.

Enteroendocrine cells sense bacterial tryptophan catabolites to activate enteric and vagal neuronal pathways.

The intestinal epithelium senses nutritional and microbial stimuli using epithelial sensory enteroendocrine cells (EEC). EECs communicate nutritional information to the nervous system, but whether they also relay signals from intestinal microbes remains unknown. Using in vivo real-time measurements of EEC and nervous system activity in zebrafish, we discovered that the bacteria Edwardsiella tarda activate EECs through the receptor transient receptor potential ankyrin A1 (Trpa1) and increase intestinal motility. Microbial, pharmacological, or optogenetic activation of Trpa1+EECs directly stimulates vagal sensory ganglia and activates cholinergic enteric neurons by secreting the neurotransmitter 5-hydroxytryptamine (5-HT). A subset of indole derivatives of tryptophan catabolism produced by E. tarda and other gut microbes activates zebrafish EEC Trpa1 signaling. These catabolites also directly stimulate human and mouse Trpa1 and intestinal 5-HT secretion. These results establish a molecular pathway by which EECs regulate enteric and vagal neuronal pathways in response to microbial signals.

Rhizolutin, a Novel 7/10/6-Tricyclic Dilactone, Dissociates Misfolded Protein Aggregates and Reduces Apoptosis/Inflammation Associated with Alzheimer's Disease.

Rhizolutin (1) was discovered as a natural product of ginseng-rhizospheric Streptomyces sp. WON17. Its structure features an unprecedented 7/10/6-tricyclic dilactone carbon skeleton composed of dimethylcyclodecatriene flanked by a 7-membered and a 6-membered lactone ring based on spectroscopic analysis. During an unbiased screening of natural product libraries, this novel compound was found to dissociate amyloid-ß (Aß) plaques and tau tangles, which are key pathological hallmarks of Alzheimer's disease (AD). Rhizolutin treatment of APP/PS1 double transgenic mice with AD significantly dissociated hippocampal plaques. In vitro, rhizolutin substantially decreased Aß-induced apoptosis and inflammation in neuronal and glial cells. Our findings introduce a unique chemical entity that targets Aß and tau concurrently by mimicking misfolded protein clearance mechanisms of immunotherapy, which is prominently investigated in clinical trials.

Donghaecyclinones A-C: New Cytotoxic Rearranged Angucyclinones from a Volcanic Island-Derived Marine Streptomyces sp.

Chemical profiling of the Streptomyces sp. strain SUD119, which was isolated from a marine sediment sample collected from a volcanic island in Korea, led to the discovery of three new metabolites: donghaecyclinones A-C (1-3). The structures of 1-3 were found to be rearranged, multicyclic, angucyclinone-class compounds according to nuclear magnetic resonance (NMR) and mass spectrometry (MS) analyses. The configurations of their stereogenic centers were successfully assigned using a combination of quantum mechanics-based computational methods for calculating the NMR shielding tensor (DP4 and CP3) as well as electronic circular dichroism (ECD) along with a modified version of Mosher's method. Donghaecyclinones A-C (1-3) displayed cytotoxicity against diverse human cancer cell lines (IC50: 6.7-9.6 µM for 3).

Nanodelivery of Mycophenolate Mofetil to the Organ Improves Transplant Vasculopathy.

Inflammation occurring within the transplanted organ from the time of harvest is an important stimulus of early alloimmune reactivity and promotes chronic allograft rejection. Chronic immune-mediated injury remains the primary obstacle to the long-term success of organ transplantation. However, organ transplantation represents a rare clinical setting in which the organ is accessible ex vivo, providing an opportunity to use nanotechnology to deliver therapeutics directly to the graft. This approach facilitates the directed delivery of immunosuppressive agents (ISA) to target local pathogenic immune responses prior to the transplantation. Here, we have developed a system of direct delivery and sustained release of mycophenolate mofetil (MMF) to treat the donor organ prior to transplantation. Perfusion of a donor mouse heart with MMF-loaded PEG-PLGA nanoparticles (MMF-NPs) prior to transplantation abrogated cardiac transplant vasculopathy by suppressing intragraft pro-inflammatory cytokines and chemokines. Our findings demonstrate that ex vivo delivery of an ISA to donor organs using a nanocarrier can serve as a clinically feasible approach to reduce transplant immunity.

Donghaesulfins A and B, Dimeric Benz[ a]anthracene Thioethers from Volcanic Island Derived Streptomyces sp.

The chemical analysis of a Streptomyces strain, from a Korean volcanic island, discovered new benz[ a]anthracene dimers linked by a thioether bond. The structures of donghaesulfins A and B (1 and 2) were elucidated by spectroscopic analysis including energy-dispersive X-ray. Their configurations were determined by ROESY NMR data, DP4 calculations, the modified Mosher's method, and ECD calculations. Donghaesulfins A (1) induced quinone reductase, whereas donghaesulfin B (2) displayed antiangiogenesis activity.

Bombyxamycins A and B, Cytotoxic Macrocyclic Lactams from an Intestinal Bacterium of the Silkworm Bombyx mori.

Bombyxamycins A and B (1 and 2) were discovered from a silkworm gut Streptomyces bacterium. Spectroscopic analysis and multiple-step chemical derivatization identified them as 26-membered cyclic lactams with polyene features. Bombyxamycin A showed significant antibacterial and antiproliferative effects. The bombyxamycin biosynthetic gene cluster was identified by genetic analysis. Gene deletion experiments confirmed that the cytochrome P450 BomK is responsible for the generation of 2, which unprecedentedly bears tetrahydrofuran in its macrocyclic ring.