Tutuilamides A–C: vinyl-chloride-containing cyclodepsipeptides from marine cyanobacteria with potent elastase inhibitory properties

Marine cyanobacteria (blue-green algae) have been shown to possess an enormous capacity to produce structurally diverse natural products that exhibit a broad spectrum of potent biological activities, including cytotoxic, antifungal, antiparasitic, antiviral, and antibacterial activities. Using mass-spectrometry-guided fractionation together with molecular networking, cyanobacterial field collections from American Samoa and Palmyra Atoll yielded three new cyclic peptides, tutuilamides A–C. Their structures were established by spectroscopic techniques including 1D and 2D NMR, HR-MS, and chemical derivatization. Structure elucidation was facilitated by employing advanced NMR techniques including nonuniform sampling in combination with the 1,1-ADEQUATE experiment. These cyclic peptides are characterized by the presence of several unusual residues including 3-amino-6-hydroxy-2-piperidone and 2-amino-2-butenoic acid, together with a novel vinyl chloride-containing residue. Tutuilamides A–C show potent elastase inhibitory activity together with moderate potency in H-460 lung cancer cell cytotoxicity assays. The binding mode to elastase was analyzed by X-ray crystallography revealing a reversible binding mode similar to the natural product lyngbyastatin 7. The presence of an additional hydrogen bond with the amino acid backbone of the flexible side chain of tutuilamide A, compared to lyngbyastatin 7, facilitates its stabilization in the elastase binding pocket and possibly explains its enhanced inhibitory potency

Tutuilamides A–C: vinyl-chloride-containing cyclodepsipeptides from marine cyanobacteria with potent elastase inhibitory properties

Marine cyanobacteria (blue-green algae) have been shown to possess an enormous capacity to produce structurally diverse natural products that exhibit a broad spectrum of potent biological activities, including cytotoxic, antifungal, antiparasitic, antiviral, and antibacterial activities. Using mass-spectrometry-guided fractionation together with molecular networking, cyanobacterial field collections from American Samoa and Palmyra Atoll yielded three new cyclic peptides, tutuilamides A–C. Their structures were established by spectroscopic techniques including 1D and 2D NMR, HR-MS, and chemical derivatization. Structure elucidation was facilitated by employing advanced NMR techniques including nonuniform sampling in combination with the 1,1-ADEQUATE experiment. These cyclic peptides are characterized by the presence of several unusual residues including 3-amino-6-hydroxy-2-piperidone and 2-amino-2-butenoic acid, together with a novel vinyl chloride-containing residue. Tutuilamides A–C show potent elastase inhibitory activity together with moderate potency in H-460 lung cancer cell cytotoxicity assays. The binding mode to elastase was analyzed by X-ray crystallography revealing a reversible binding mode similar to the natural product lyngbyastatin 7. The presence of an additional hydrogen bond with the amino acid backbone of the flexible side chain of tutuilamide A, compared to lyngbyastatin 7, facilitates its stabilization in the elastase binding pocket and possibly explains its enhanced inhibitory potency

Advances in exploring the therapeutic potential of marine natural products

Marine natural products represent novel and diverse chemotypes that serve as templates for the discovery and development of therapeutic agents with distinct mechanisms of action. These genetically encoded compounds produced by an evolutionary optimized biosynthetic machinery are usually quite complex and can be difficult to recreate in the laboratory. The isolation from the source organism results in limited amount of material; however, the development of advanced NMR technologies and dereplication strategies has enabled the structure elucidation on small scale. In order to rigorously explore the therapeutic potential of marine natural products and advance them further, the biological characterization has to keep pace with the chemical characterization. The limited marine natural product supply has been a serious challenge for thorough investigation of the biological targets. Several marine drugs have reached the markets or are in clinical trials, where those challenges have been overcome, including through the development of scalable syntheses. However, the identification of mechanisms of action of marine natural products early in the discovery process is potentially game changing, since effectively linking marine natural products to potential therapeutic applications in turn triggers motivation to tackle challenging syntheses and solve the supply problem. An increasing number of sensitive technologies and methods have been developed in recent years, some of which have been successfully applied to marine natural products, increasing the value of these compounds with respect to their biomedical utility. In this review, we discuss advances in overcoming the bottlenecks in marine natural product research, emphasizing on the development and advances of diverse target identification technologies applicable for marine natural product research

Effect of Pricking-bloodletting Therapy Combined with Zhuang-medicine-thread Moxibustion on TLRs/MyD88 Signal Pathway in a Rat Model of Acute Gouty Arthritis

Background With the change of people's environment and diet structure, acute gouty arthritis (AGA) has become a common clinical disease, which is prone to recurrence, causing harm to patients' health. Pricking-bloodletting therapy combined with Zhuang-medicine-thread moxibustion (moxibustion with a threat prepared with Zhuang herbal medicine) has proven to have a definite therapeutic effect on AGA clinically, but the mechanism of action is not very clear. Objective To assess the effect of pricking-bloodletting therapy combined with Zhuang-medicine-thread moxibustion on toll-like receptors /myeloid differentiation factor 88 (TLRs/MyD88) signal pathway in a rat model of AGA to explore the mechanism of action of this treatment in AGA. Methods The experiment lasted from May 2021 to March 2022, sixty SD rats were equally randomized into 6 groups: blank group, model group, pricking-bloodletting group, medicated thread group, colchicine group and pricking-bloodletting with medicated thread group. Except for the blank group, the other groups received sodium urate suspension injected into the right ankle cavity to prepare the AGA model. Twenty-four hours after the modelling, colchicine group received intragastric administration of colchicine suspension, pricking-bloodletting group received bloodletting after pricking the Ashi acupoint with a needle, medicated thread group received Zhuang-medicine-thread moxibustion at the site of lesion, and pricking-bloodletting with medicated thread group first received bloodletting after pricking the Ashi acupoint with a needle, then Zhuang-medicine-thread moxibustion at the site of lesion. The swelling degree of the right ankle joint was observed at 6, 12, 24 h and 72 h after modeling. Hematoxylin-eosin staining was used to observe the pathological changes of the synovium of the right ankle joint. The serum levels of interleukin (IL) -10, IL-8 and cyclooxygenase-2 (COX-2) were determined by ELISA. The expressions of MyD88 and IKK-β in the synovium of the right ankle were detected by western blotting. Results The transverse diameter of right lateral malleolus in model group, pricking-bloodletting group, medicated thread group or colchicine group was larger than that in blank group at 6, 12, 24, 48 h and 72 h after modeling (P<0.05). The transverse diameter of right lateral malleolus in pricking-bloodletting with medicated thread group was larger than that in blank group at 6, 12, 24 h and 48 h after modeling (P<0.05). The transverse diameter of the right lateral malleolus of the pricking-bloodletting group, medicated thread group, colchicine group or pricking-bloodletting with medicated thread group was smaller than that of the model group at 48 h and 72 h after modeling (P<0.05). Compared with model group, the inflammatory cell infiltration of right ankle in pricking-bloodletting group, medicated thread group, colchicine group and pricking-bloodletting with medicated thread group was improved. The blank group had lower levels of IL-8 and COX-2 and higher level of IL-10 than each of the other 5 groups (P<0.05). The model group had higher levels of IL-8 and COX-2 and lower level of IL-10 than colchicine group, pricking-bloodletting with medicated thread group, pricking-bloodletting group or medicated thread group (P<0.05). The colchicine group had lower levels of IL-8 and COX-2 and higher level of IL-10 than pricking-bloodletting group or medicated thread group (P<0.05). The pricking-bloodletting with medicated thread group had lower levels of IL-8 and COX-2 and higher level of IL-10 than pricking-bloodletting group or medicated thread group (P<0.05). The blank group had lower level of MyD88 than each of the other 5 groups (P<0.05). The blank group had lower level of IKK-β than model group, medicated thread group, pricking-bloodletting group or pricking-bloodletting with medicated thread group (P<0.05). The model group had higher IKK-β level than medicated thread group or colchicine group (P<0.05). The model group had higher MyD8 level than medicated thread group, colchicine group, pricking-bloodletting group or pricking-bloodletting with medicated thread group (P<0.05) . Conclusion Pricking-bloodletting with Zhuang-medicine-thread moxibustion is effective in improving the symptoms of AGA by regulating the TLRs/MyD88 signaling pathway, which may be a potential alternative therapy for AGA

Total Synthesis of the Potent Marine-Derived Elastase Inhibitor Lyngbyastatin 7 and in Vitro Biological Evaluation in Model Systems for Pulmonary Diseases

Lyngbyastatin 7 (<b>1</b>) is a marine cyanobacteria-derived lariat-type cyclic depsipeptide of which the macrocyclic core possesses modified amino acids, including a featured 3-amino-6-hydroxy-2-piperidone (Ahp) moiety and a (<i>Z</i>)-2-amino-2-butenoic acid (Abu) moiety. The first total synthesis of <b>1</b> was successfully established via 31 steps, and the conditions of several crucial steps were optimized to ensure smooth operations. The previously reported structural assignment and elastase inhibitory activity of the isolated natural product were confirmed. According to the extensive in vitro biological evaluation, compound <b>1</b> displayed low nanomolar IC₅₀ in blocking elastase activity and strong ability in protecting bronchial epithelial cells against elastase-induced antiproliferation and abrogating the elastase-triggered induction of pro-inflammatory cytokine expression. Its overall performance was superior over sivelestat, the only approved small molecule drug targeting elastase, which indicated its potential in developing as a pharmacotherapeutic against elastase-mediated pathologies. The success in total synthesis, designed with a novel convergent strategy, not only overcame the supply issue for thorough preclinical studies but also paved the way for convenient synthesis of analogues with improved potency and druglike properties

Isolation, Structure Elucidation and Biological Evaluation of Lagunamide D: A New Cytotoxic Macrocyclic Depsipeptide from Marine Cyanobacteria

Lagunamide D, a new cytotoxic macrocyclic depsipeptide, was discovered from a collection of marine cyanobacteria from Loggerhead Key in the Dry Tortugas, Florida. An intramolecular ester exchange was observed, where the 26-membered macrocycle could contract to a 24-membered compound via acyl migration at the 1,3-diol unit, and the transformation product was named lagunamide D&#8217;. The planar structures of both compounds were elucidated using a combination of nuclear magnetic resonance (NMR) spectroscopy and high-resolution mass spectroscopy (HRMS). The absolute configurations were determined on the basis of enantioselective analysis, modified Mosher&#8217;s analysis, Kishi NMR database, and direct comparison with lagunamide A, a structure closely resembling lagunamide D. Lagunamides A and D displayed low-nanomolar antiproliferative activity against A549 human lung adenocarcinoma cells, while the structural transformation from the 26-membered lagunamide D macrocycle to the 24-membered ring structure for lagunamide D&#8217; led to a 9.6-fold decrease in activity. Lagunamide D also displayed potent activity in triggering apoptosis in a dose- and time-dependent manner. Further investigation on the mechanism of action of the lagunamide scaffold is needed to fully explore its therapeutic potential as an anticancer agent

Tutuilamides A–C: Vinyl-Chloride-Containing Cyclodepsipeptides from Marine Cyanobacteria with Potent Elastase Inhibitory Properties

Marine cyanobacteria (blue-green algae) have been shown to possess an enormous capacity to produce structurally diverse natural products that exhibit a broad spectrum of potent biological activities, including cytotoxic, antifungal, antiparasitic, antiviral, and antibacterial activities. Using mass-spectrometry-guided fractionation together with molecular networking, cyanobacterial field collections from American Samoa and Palmyra Atoll yielded three new cyclic peptides, tutuilamides A-C. Their structures were established by spectroscopic techniques including 1D and 2D NMR, HR-MS, and chemical derivatization. Structure elucidation was facilitated by employing advanced NMR techniques including nonuniform sampling in combination with the 1,1-ADEQUATE experiment. These cyclic peptides are characterized by the presence of several unusual residues including 3-amino-6-hydroxy-2-piperidone and 2-amino-2-butenoic acid, together with a novel vinyl chloride-containing residue. Tutuilamides A-C show potent elastase inhibitory activity together with moderate potency in H-460 lung cancer cell cytotoxicity assays. The binding mode to elastase was analyzed by X-ray crystallography revealing a reversible binding mode similar to the natural product lyngbyastatin 7. The presence of an additional hydrogen bond with the amino acid backbone of the flexible side chain of tutuilamide A, compared to lyngbyastatin 7, facilitates its stabilization in the elastase binding pocket and possibly explains its enhanced inhibitory potency