N-Desmethylmajusculamide B, a lipopeptide isolated from the Okinawan cyanobacterium Okeania hirsuta

A new lipopeptide, N-desmethylmajusculamide B (1), was isolated from the Okinawan cyanobacterium Okeania hirsuta along with 2 known compounds majusculamide A (2) and majusculamide B (3). The planar structure of (1) was elucidated by a detailed analysis of mass spectrometry and nuclear magnetic resonance spectra. The absolute configurations of the amino acid residues were determined using Marfey's analysis. The configuration of C-16 in the α-methyl-β-keto-decanoyl moiety was determined unambiguously to be S by conducting a semisynthesis of N-desmethylmajusculamide B from 3. The cytotoxicity against mouse L1210 leukemia cells was evaluated for majusculamides (1-3).

A Semisynthesis Platform for the Efficient Production and Exploration of Didemnin-Based Drugs

Plitidepsin (or dehydrodidemnin B), an approved anticancer drug, belongs to the didemnin family of cyclic depsipeptides, which are found in limited quantities in marine tunicate extracts. Herein, we introduce a new approach that integrates microbial and chemical synthesis to generate plitidepsin and its analogues. We screened a Tistrella strain library to identify a potent didemnin B producer, and then introduced a second copy of the didemnin biosynthetic gene cluster into its genome, resulting in a didemnin B titer of approximately 75 mg/L. Next, we developed two straightforward chemical strategies to convert didemnin B into plitidepsin, one of which involved a one-step synthetic route giving over 90 % overall yield. Furthermore, we synthesized 13 new didemnin derivatives and three didemnin probes, enabling research into structure-activity relationships and interactions between didemnin and proteins. Our study highlights the synergistic potential of biosynthesis and chemical synthesis in overcoming the challenge of producing complex natural products sustainably and at scale.

Forgotten Natural Products: Semisynthetic Development of Blasticidin S As an Antibiotic Lead

Forgotten natural products offer value as antimicrobial scaffolds, providing diverse mechanisms of action that complement existing antibiotic classes. This study focuses on the derivatization of the cytotoxin blasticidin S, seeking to leverage its unique ribosome inhibition mechanism. Despite its complex zwitterionic properties, a selective protection and amidation strategy enabled the creation of a library of blasticidin S derivatives including the natural product P10. The amides exhibited significantly increased activity against Gram-positive bacteria and enhanced specificity for pathogenic bacteria over human cells. Molecular docking and computational property analysis suggested variable binding poses and indicated a potential correlation between cLogP values and activity. This work demonstrates how densely functionalized forgotten antimicrobials can be straightforwardly modified, enabling the further development of blasticidin S derivatives as lead compounds for a novel class of antibiotics.

Antiviral and antibacterial properties of phloroglucinols: a review on naturally occurring and (semi)synthetic derivatives with potential therapeutic interest

Phloroglucinol and derived compounds comprise a huge class of secondary metabolites widely distributed in plants and brown algae. A vast array of biological activities, including antioxidant, anti-inflammatory, antimicrobial, and anticancer has been associated to this class of compounds. In this review, the available data on the antiviral and antibacterial capacity of phloroglucinols have been analyzed. Some of these compounds and derivatives show important antimicrobial properties in vitro. Phloroglucinols have been shown to be effective against viruses, such as human immunodeficiency virus (HIV), herpes or enterovirus, and preliminary data through docking analysis suggest that they can be effective against SARS-CoV-19. Also, some phloroglucinols derivatives have shown antibacterial effects against diverse bacteria strains, including Bacillus subtilis and Staphylococcus aureus, and (semi)synthetic development of novel compounds have led to phloroglucinols with a significantly increased biological activity. However, therapeutic use of these compounds is hindered by the absence of in vivo studies and scarcity of information on their mechanisms of action, and hence further research efforts are required. On the basis of this consideration, our work aims to gather data regarding the efficacy of natural-occurring and synthetic phloroglucinol derivatives as antiviral and antibacterial agents against human pathogens, which have been published during the last three decades. The recollection of results reported in this review represents a valuable source of updated information that will potentially help researchers in the development of novel antimicrobial agents.

Semisynthesis of A6-A11 lactam insulin

Insulin replacement therapy is essential for the management of diabetes. However, despite the relative success of this therapeutic strategy, there is still a need to improve glycaemic control and the overall quality of life of patients. This need has driven research into orally available, glucose-responsive and rapid-acting insulins. A key consideration during analogue development is formulation stability, which can be improved via the replacement of insulin's A6-A11 disulfide bond with stable mimetics. Unfortunately, analogues such as these require extensive chemical synthesis to incorporate the nonnative cross-links, which is not a scalable synthetic approach. To address this issue, we demonstrate proof of principle for the semisynthesis of insulin analogues bearing nonnative A6-A11 cystine isosteres. The key feature of our synthetic strategy involves the use of several biosynthetically derived peptide precursors which can be produced at scale cost-effectively and a small, chemically synthesised A6-A11 macrocyclic lactam fragment. Although the assembled A6-A11 lactam insulin possesses poor biological activity in vitro, our synthetic strategy can be applied to other disulfide mimetics that have been shown to improve thermal stability without significantly affecting activity and structure. Moreover, we envisage that this new semisynthetic approach will underpin a new generation of hyperstable proteomimetics.

Semisynthesis and Cytotoxic Evaluation of an Ether Analogue Library Based on a Polyhalogenated Diphenyl Ether Scaffold Isolated from a Lamellodysidea Sponge

The known oxygenated polyhalogenated diphenyl ether, 2-(2',4'-dibromophenoxy)-3,5-dibromophenol (1), with previously reported activity in multiple cytotoxicity assays was isolated from the sponge Lamellodysidea sp. and proved to be an amenable scaffold for semisynthetic library generation. The phenol group of 1 was targeted to generate 12 ether analogues in low-to-excellent yields, and the new library was fully characterized by NMR, UV, and MS analyses. The chemical structures for 2, 8, and 9 were additionally determined via single-crystal X-ray diffraction analysis. All natural and semisynthetic compounds were evaluated for their ability to inhibit the growth of DU145, LNCaP, MCF-7, and MDA-MB-231 cancer cell lines. Compound 3 was shown to have near-equivalent activity compared to scaffold 1 in two in vitro assays, and the activity of the compounds with an additional benzyl ring appeared to be reliant on the presence and position of additional halogens.

Phenolic Substitution in Fidaxomicin: A Semisynthetic Approach to Antibiotic Activity Across Species

Fidaxomicin (Fdx) is a natural product antibiotic with potent activity against Clostridioides difficile and other Gram-positive bacteria such as Mycobacterium tuberculosis. Only a few Fdx derivatives have been synthesized and examined for their biological activity in the 50 years since its discovery. Fdx has a well-studied mechanism of action, namely inhibition of the bacterial RNA polymerase. Yet, the targeted organisms harbor different target protein sequences, which poses a challenge for the rational development of new semisynthetic Fdx derivatives. We introduced substituents on the two phenolic hydroxy groups of Fdx and evaluated the resulting trends in antibiotic activity against M. tuberculosis, C. difficile, and the Gram-negative model organism Caulobacter crescentus. As suggested by the target protein structures, we identified the preferable derivatisation site for each organism. The derivative ortho-methyl Fdx also exhibited activity against the Gram-negative C. crescentus wild type, a first for fidaxomicin antibiotics. These insights will guide the synthesis of next-generation fidaxomicin antibiotics.

Regioselective and Stereoselective Synthesis of Parthenolide Analogs by Acyl Nitroso-Ene Reaction and Their Biological Evaluation against Mycobacterium tuberculosis

Historically, natural products have played a major role in the development of antibiotics. Their complex chemical structures and high polarity give them advantages in the drug discovery process. In the broad range of natural products, sesquiterpene lactones are interesting compounds because of their diverse biological activities, their high-polarity, and sp3-carbon-rich chemical structures. Parthenolide (PTL) is a natural compound isolated from Tanacetum parthenium, of the family of germacranolide-type sesquiterpene lactones. In recent years, parthenolide has been studied for its anti-inflammatory, antimigraine, and anticancer properties. Recently, PTL has shown antibacterial activities, especially against Gram-positive bacteria. However, few studies are available on the potential antitubercular activities of parthenolide and its analogs. It has been demonstrated that parthenolide's biological effects are linked to the reactivity of α-exo-methylene-γ-butyrolactone, which reacts with cysteine in targeted proteins via a Michael addition. In this work, we describe the ene reaction of acylnitroso intermediates with parthenolide leading to the regioselective and stereoselective synthesis of new derivatives and their biological evaluation. The addition of hydroxycarbamates and hydroxyureas led to original analogs with higher polarity and solubility than parthenolide. Through this synthetic route, the Michael acceptor motif was preserved and is thus believed to be involved in the selective activity against Mycobacterium tuberculosis.

From Plant to Chemistry: Sources of Active Opioid Antinociceptive Principles for Medicinal Chemistry and Drug Design

Pain continues to be an enormous global health challenge, with millions of new untreated or inadequately treated patients reported annually. With respect to current clinical applications, opioids remain the mainstay for the treatment of pain, although they are often associated with serious side effects. To optimize their tolerability profiles, medicinal chemistry continues to study novel ligands and innovative approaches. Among them, natural products are known to be a rich source of lead compounds for drug discovery, and they hold potential for pain management. Traditional medicine has had a long history in clinical practice due to the fact that nature provides a rich source of active principles. For instance, opium had been used for pain management until the 19th century when its individual components, such as morphine, were purified and identified. In this review article, we conducted a literature survey aimed at identifying natural products interacting either directly with opioid receptors or indirectly through other mechanisms controlling opioid receptor signaling, whose structures could be interesting from a drug design perspective.

Nature-Inspired Compounds: Synthesis and Antibacterial Susceptibility Testing of Eugenol Derivatives against H. pylori Strains

The antimicrobial properties of one of the most important secondary metabolites, Eugenol (EU), inspired us to design and synthesize three different series of derivatives enhancing its parent compound's anti-Helicobacter pylori activity. Thus, we prepared semisynthetic derivatives through (A) diazo aryl functionalization, (B) derivatization of the hydroxy group of EU, and (C) elongation of the allyl radical by incorporating a chalcogen atom. The antibacterial evaluation was performed on the reference NCTC 11637 strain and on three drug-resistant clinical isolates and the minimal inhibitory and bactericidal concentrations (MICs and MBCs) highlight the role of chalcogens in enhancing the antimicrobial activity (less than 4 µg/mL for some compounds) of the EU scaffold (32-64 µg/mL).

Evaluation of Anticancer and Anti-Inflammatory Activities of Some Synthetic Rearranged Abietanes

Synthesis of the rearranged abietane diterpenes pygmaeocins C and D, viridoquinone, saprorthoquinone, and 1-deoxyviroxocine has been successfully achieved. The anticancer and anti-inflammatory activities of selected orthoquinonic compounds 5, 7, 13, and 19, as well as pygmaeocin C (17), were evaluated for the first time. The antitumor properties were assessed using three cancer cell lines: HT29 colon cancer cells, Hep G2 hepatocellular carcinoma cells, and B16-F10 murine melanoma cells. Compounds 5 and 13 showed the highest cytotoxicity in HT29 cells (IC50 = 6.69 ± 1.2 µg/mL and IC50 = 2.7 ± 0.8 µg/mL, respectively). Cytometric studies showed that this growth inhibition involved phase S cell cycle arrest and apoptosis induction, possibly through the activation of the intrinsic apoptotic pathway. Morphological apoptotic changes, including nuclear fragmentation and chromatin condensation, were also observed. Furthermore, the anti-inflammatory activity of these compounds was evaluated on the basis of their ability to inhibit nitric oxide production on the lipopolysaccharide activated RAW 264.7 macrophage cell line. Although all compounds showed high anti-inflammatory activity, with percentages between 40 and 100%, the highest anti-inflammatory potential was obtained by pygmaeocin B (5) (IC50NO = 33.0 ± 0.8 ng/mL). Our results suggest that due to their dual roles, this type of compound could represent a new strategy, contributing to the development of novel anticancer agents.

Anti-Diabetic Activity of Glycyrrhetinic Acid Derivatives FC-114 and FC-122: Scale-Up, In Silico, In Vitro, and In Vivo Studies

Type 2 diabetes (T2D) is one of the most common diseases and the 8th leading cause of death worldwide. Individuals with T2D are at risk for several health complications that reduce their life expectancy and quality of life. Although several drugs for treating T2D are currently available, many of them have reported side effects ranging from mild to severe. In this work, we present the synthesis in a gram-scale as well as the in silico and in vitro activity of two semisynthetic glycyrrhetinic acid (GA) derivatives (namely FC-114 and FC-122) against Protein Tyrosine Phosphatase 1B (PTP1B) and α-glucosidase enzymes. Furthermore, the in vitro cytotoxicity assay on Human Foreskin fibroblast and the in vivo acute oral toxicity was also conducted. The anti-diabetic activity was determined in streptozotocin-induced diabetic rats after oral administration with FC-114 or FC-122. Results showed that both GA derivatives have potent PTP1B inhibitory activity being FC-122, a dual PTP1B/α-glucosidase inhibitor that could increase insulin sensitivity and reduce intestinal glucose absorption. Molecular docking, molecular dynamics, and enzymatic kinetics studies revealed the inhibition mechanism of FC-122 against α-glucosidase. Both GA derivatives were safe and showed better anti-diabetic activity in vivo than the reference drug acarbose. Moreover, FC-114 improves insulin levels while decreasing LDL and total cholesterol levels without decreasing HDL cholesterol.

Light-Mediated Transformation of Renieramycins and Semisynthesis of 4'-Pyridinecarbonyl-Substituted Renieramycin-Type Derivatives as Potential Cytotoxic Agents against Non-Small-Cell Lung Cancer Cells

The semisynthesis of renieramycin-type derivatives was achieved under mild and facile conditions by attaching a 1,3-dioxole-bridged phenolic moiety onto ring A of the renieramycin structure and adding a 4'-pyridinecarbonyl ester substituent at its C-5 or C-22 position. These were accomplished through a light-induced intramolecular photoredox reaction using blue light (4 W) and Steglich esterification, respectively. Renieramycin M (4), a bis-tetrahydroisoquinolinequinone compound isolated from the Thai blue sponge (Xestospongia sp.), served as the starting material. The cytotoxicity of the 10 natural and semisynthesized renieramycins against non-small-cell lung cancer (NSCLC) cell lines was evaluated. The 5-O-(4'-pyridinecarbonyl) renieramycin T (11) compound exhibited high cytotoxicity with half-maximal inhibitory concentration (IC₅₀) values of 35.27 ± 1.09 and 34.77 ± 2.19 nM against H290 and H460 cells, respectively. Notably, the potency of compound 11 was 2-fold more than that of renieramycin T (7) and equal to those of 4 and doxorubicin. Interestingly, the renieramycin-type derivatives with a hydroxyl group at C-5 and C-22 exhibited weak cytotoxicity. In silico molecular docking and dynamics studies confirmed that the mitogen-activated proteins, kinase 1 and 3 (MAPK1 and MAPK3), are suitable targets for 11. Thus, the structure-cytotoxicity study of renieramycins was extended to facilitate the development of potential anticancer agents for NSCLC cells.

New theobromine derivatives inhibiting VEGFR-2: design, synthesis, antiproliferative, docking and molecular dynamics simulations

Background: VEGFR-2 is one of the most effective targets in cancer treatment. Aim: The design and semi-synthesis of new theobromine derivatives as potential VEGFR-2 inhibitors. Methods: In vitro and in silico evaluation of the synthesized compounds. Results: Compound 5b demonstrated excellent antiproliferative and VEGFR-2 inhibitory effects with significant apoptotic activity. It modulated the immune response by increasing IL-2 and reducing TNF-α levels. Docking and molecular dynamics simulations revealed the compound's binding affinity with VEGFR-2. Lastly, computational absorption, distribution, metabolism, excretion and toxicity studies indicated the high potential of compound 5b for drug development. Conclusion: Compound 5b could be a promising anticancer agent targeting VEGFR-2.

Perplexing Polyphenolics: The Isolations, Syntheses, Reappraisals, and Bioactivities of Flavonoids, Isoflavonoids, and Neoflavonoids from 2016 to 2022

Flavonoids, isoflavonoids, neoflavonoids, and their various subcategories are polyphenolics-an extensive class of natural products. These compounds are bioactive and display multiple activities, including anticancer, antibacterial, antiviral, antioxidant, and neuroprotective activities. Thus, these compounds can serve as leads for therapeutic agents or targets for complex synthesis; they are coveted and routinely isolated, characterized, biologically evaluated, and synthesized. However, data regarding the compounds' sources, isolation procedures, structural novelties, bioactivities, and synthetic schemes are often dispersed and complex, a dilemma this review aims to address. To serve as an easily accessible guide for researchers wanting to apprise themselves of the latest advancements in this subfield, this review summarizes seventy-six (76) articles published between 2016 and 2022 that detail the isolation and characterization of two hundred and forty-nine (249) novel compounds, the total and semisyntheses of thirteen (13) compounds, and reappraisals of the structures of twenty (20) previously reported compounds and their bioactivities. This article also discusses new synthetic methods and enzymes capable of producing or modifying flavonoids, isoflavonoids, or neoflavonoids.

Semisynthetic Sesquiterpene Lactones Generated by the Sensibility of Glaucolide B to Lewis and Brønsted-Lowry Acids and Bases: Cytotoxicity and Anti-Inflammatory Activities

Sesquiterpene lactone (SL) subtypes including hirsutinolide and cadinanolide have a controversial genesis. Metabolites of these classes are either described as natural products or as artifacts produced via the influence of solvents, chromatographic mobile phases, and adsorbents used in phytochemical studies. Based on this divergence, and to better understand the sensibility of these metabolites, different pH conditions were used to prepare semisynthetic SLs and evaluate the anti-inflammatory and antiproliferative activities. Therefore, glaucolide B (1) was treated with various Brønsted-Lowry and Lewis acids and bases-the same approach was applied to some of its derivatives-allowing us to obtain 14 semisynthetic SL derivatives, 10 of which are hereby reported for the first time. Hirsutinolide derivatives 7a (CC₅₀ = 5.0 µM; SI = 2.5) and 7b (CC₅₀ = 11.2 µM; SI = 2.5) and the germacranolide derivative 8a (CC₅₀ = 3.1 µM; SI = 3.0) revealed significant cytotoxic activity and selectivity against human melanoma SK-MEL-28 cells when compared with that against non-tumoral HUVEC cells. Additionally, compounds 7a and 7c.1 showed strongly reduced interleukin-6 (IL-6) and nitrite (NOx) release in pre-treated M1 macrophages J774A.1 when stimulated with lipopolysaccharide. Despite the fact that hirsutinolide and cadinanolide SLs may be produced via plant metabolism, this study shows that acidic and alkaline extraction and solid-phase purification processes can promote their formation.

Psammaplysins: Insights from Natural Sources, Structural Variations, and Pharmacological Properties

Marine natural products (MNPs) continue to be in the spotlight in the global drug discovery endeavor. Currently, more than 32,000 structurally diverse secondary metabolites from marine sources have been isolated, making MNPs a vital source for researchers to look for novel drug candidates. The marine-derived psammaplysins possess the rare and unique 1,6-dioxa-2-azaspiro [4.6] undecane backbone and are represented by 44 compounds in the literature, mostly from sponges of the order Verongiida. Compounds with 1,6-dioxa-2-azaspiro [4.6] undecane moiety exist in the literature under five names, including psammaplysins, ceratinamides, frondoplysins, ceratinadins, and psammaceratins. These compounds displayed significant biological properties including growth inhibitory, antimalarial, antifouling, protein tyrosine phosphatase inhibition, antiviral, immunosuppressive, and antioxidant effects. In this review, a comprehensive literature survey covering natural occurrence of the psammaplysins and related compounds, methods of isolation, structural differences, the biogenesis, and biological/pharmacological properties, will be presented.

Photodynamic Inactivation of Microorganisms Using Semisynthetic Chlorophyll a Derivatives as Photosensitizers

In this study, we describe the semisynthesis of cost-effective photosensitizers (PSs) derived from chlorophyll a containing different substituents and using previously described methods from the literature. We compared their structures when used in photodynamic inactivation (PDI) against Staphylococcus aureus, Escherichia coli, and Candida albicans under different conditions. The PSs containing carboxylic acids and butyl groups were highly effective against S. aureus and C. albicans following our PDI protocol. Overall, our results indicate that these nature-inspired PSs are a promising alternative to selectively inactivate microorganisms using PDI.

Synthesis and Biological Evaluation of Cassane Diterpene (5α)-Vuacapane-8(14), 9(11)-Diene and of Some Related Compounds

A set of thirteen cassane-type diterpenes was synthesized and an expedient synthetic route was used to evaluate 14-desmethyl analogs of the most active tested cassane. The anti-inflammatory activities of these 13 compounds were evaluated on a lipopolysaccharide (LPS)-activated RAW 264.7 cell line by inhibition of nitric oxide (NO) production, some of them reaching 100% NO inhibition after 72 h of treatment. The greatest anti-inflammatory effect was observed for compounds 16 and 20 with an IC_{50 NO} of 2.98 ± 0.04 μg/mL and 5.71 ± 0.14 μg/mL, respectively. Flow-cytometry analysis was used to determine the cell cycle distribution and showed that the inhibition in NO release was accompanied by a reversion of the differentiation processes. Moreover, the anti-cancer potential of these 13 compounds were evaluated in three tumor cell lines (B16-F10, HT29, and Hep G2). The strongest cytotoxic effect was achieved by salicylaldehyde 20, and pterolobirin G (6), with IC₅₀ values around 3 μg/mL in HT29 cells, with total apoptosis rates 80% at IC₈₀ concentrations, producing a significant cell-cycle arrest in the G0/G1 phase, and a possible activation of the extrinsic apoptotic pathway. Additionally, initial SAR data analysis showed that the methyl group at the C-14 positions of cassane diterpenoids is not always important for their cytotoxic and anti-inflammatory activities.

Recent Advances in the Development of Semisynthetic Glycopeptide Antibiotics: 2014-2022

The accelerated appearance of drug-resistant bacteria poses an ever-growing threat to modern medicine's capacity to fight infectious diseases. Gram-positive species such as methicillin-resistant Staphylococcus aureus (MRSA) and Streptococcus pneumoniae continue to contribute significantly to the global burden of antimicrobial resistance. For decades, the treatment of serious Gram-positive infections relied upon the glycopeptide family of antibiotics, typified by vancomycin, as a last line of defense. With the emergence of vancomycin resistance, the semisynthetic glycopeptides telavancin, dalbavancin, and oritavancin were developed. The clinical use of these compounds is somewhat limited due to toxicity concerns and their unusual pharmacokinetics, highlighting the importance of developing next-generation semisynthetic glycopeptides with enhanced antibacterial activities and improved safety profiles. This Review provides an updated overview of recent advancements made in the development of novel semisynthetic glycopeptides, spanning the period from 2014 to today. A wide range of approaches are covered, encompassing innovative strategies that have delivered semisynthetic glycopeptides with potent activities against Gram-positive bacteria, including drug-resistant strains. We also address recent efforts aimed at developing targeted therapies and advances made in extending the activity of the glycopeptides toward Gram-negative organisms.

Semisynthetic triterpenes led to the generation of selective antitrypanosomal lead compounds

Triterpenes α,β-amyrin are naturally occurring molecules that can serve as building blocks for synthesizing new chemical entities. This study synthesized acyl, carboxyesther, NSAID, and nitrogenous derivatives and evaluated their antimicrobial activity. A cyclodextrin complexation method was developed to improve the solubility of the derivatives. Of the 17 derivatives tested, five exhibited activity against Trypanosoma cruzi, T. brucei, Leishmania infantum, Candida albicans, Staphylococcus aureus, and Escherichia coli. The 9a/9b mixture showed weak activity against the parasites (IC₅₀ 24.45-40.32 μM). However, it showed no activity for the other microorganisms. Derivatives 14a/14b exhibited potent activity against T. cruzi (IC₅₀ 2.0 nM) in this tested concentration did not show activity to the other microorganisms and were not cytotoxic. Derivatives 15a/15b and 16a/16b demonstrated relevant activity against the parasites (IC₅₀ 2.24-5.44 μM), but were also cytotoxic. Derivatives 17a/17b showed low activity against the tested parasites (IC₅₀ 21.70-22.79 μM), but they were selective since they did not show activity against other microorganisms. In docking studies, in general, all derivatives showed complementarity with the CYP51 binding site of the trypanosomatid mainly by hydrophobic interactions; thus, it is not conclusive that the molecules act by inhibiting this enzyme. Our results showed that triterpenes derivatives with antitrypanosomal activity could be synthesized by an inexpensive and rapid method.

A Review of Modifications of Quinoline Antimalarials: Mefloquine and (hydroxy)Chloroquine

Late-stage modification of drug molecules is a fast method to introduce diversity into the already biologically active scaffold. A notable number of analogs of mefloquine, chloroquine, and hydroxychloroquine have been synthesized, starting from the readily available active pharmaceutical ingredient (API). In the current review, all the modifications sites and reactivity types are summarized and provide insight into the chemistry of these molecules. The approaches include the introduction of simple groups and functionalities. Coupling to other drugs, polymers, or carriers afforded hybrid compounds or conjugates with either easily hydrolyzable or more chemically inert bonds. The utility of some of the compounds was tested in antiprotozoal, antibacterial, and antiproliferative assays, as well as in enantiodifferentiation experiments.

Chemical Synthesis and Semisynthesis of Lipidated Proteins

Lipidation is a ubiquitous modification of peptides and proteins that can occur either co‐ or post‐translationally. An array of different lipid classes can adorn proteins and has been shown to influence a number of crucial biological activities, including the regulation of signaling, cell–cell adhesion events, and the anchoring of proteins to lipid rafts and phospholipid membranes. Whereas nature employs a range of enzymes to install lipid modifications onto proteins, the use of these for the chemoenzymatic generation of lipidated proteins is often inefficient or impractical. An alternative is to harness the power of modern synthetic and semisynthetic technologies to access lipid‐modified proteins in a pure and homogeneously modified form. This Review aims to highlight significant advances in the development of lipidation and ligation chemistry and their implementation in the synthesis and semisynthesis of homogeneous lipidated proteins that have enabled the influence of these modifications on protein structure and function to be uncovered.

Spirodiclofen ether derivatives: semisynthesis, structural elucidation, and pesticidal activities against Tetranychus cinnabarinus Boisduval, Aphis citricola Van der Goot and Mythimna separata Walker

BACKGROUND

Spirodiclofen is a spirocyclic tetronic acid-type acaricidal agent. Nowadays, serious pests resistance to spirodiclofen and cross-resistance to other acaricides has appeared. To overcome pests resistance and discover new potential agrochemicals, a series of ether derivatives were prepared based on spirodiclofen as a lead compound. Their pesticidal activities were investigated against three typically agricultural pests, Mythimna separata Walker, Aphis citricola Van der Goot and Tetranychus cinnabarinus Boisduval.

RESULTS

Four steric structures of compounds 5e, 5f, 5i and 5j were determined by single-crystal X-ray diffraction. Against T. cinnabarinus, compounds 5b, 5f and 5l exhibited potent acaricidal activity, and their good control effects in the glasshouse were observed when compared with spirodiclofen, especially the control efficiency of compound 5b was comparable to that of spirodiclofen; against M. separata, compound 5j showed > 1.8-fold potent insecticidal activity of spirodiclofen; against A. citricola, compounds 5d and 5j displayed > 2.0-fold potent aphicidal activity of spirodiclofen. The relationships between their structures and agricultural activities were also discussed.

CONCLUSION

Compounds 5b and 5d could be further studied as acaricidal and aphicidal agents, respectively; compound 5j can be considered as a lead compound for the insecticidal and aphicidal activities. This will pave the way for future application of these derivatives as pesticide substitutes for spirodiclofen. © 2021 Society of Chemical Industry.

Cephalodiones A-D: Compound Characterization and Semisynthesis by [6+6] Cycloaddition

Cephalodiones A-D (1-4), the first example of C₁₉ -norditerpenoid dimers, were isolated and fully characterized from a Cephalotaxus plant. These new skeletal natural products shared a unique tricyclo[6.4.1.1^2,7 ]tetradeca-3,5,9,11-tetraene-13,14-dione core that was capped in both ends with rigid multicyclic ring systems either C₂ -symmetrically or asymmetrically. Compounds 1-4 were proposed to be biosynthetically produced by the [6+6]-cycloaddition of two identical C₁₉ -norditerpenoid troponoids, which was validated by the semisyntheses of dimers 2-4. Moreover, some compounds showed significant inhibition on Th17 cell differentiation.

SynBio-SynChem Approaches to Diversifying the Pacidamycins through the Exploitation of an Observed Pictet-Spengler Reaction

A nonenzymatic Pictet-Spengler reaction has been postulated to give rise to a subset of naturally occurring uridyl peptide antibiotics (UPAs). Here, using a combination of strain engineering and synthetic chemistry, we demonstrate that Pictet-Spengler chemistry may be employed to generate even greater diversity in the UPAs. We use an engineered strain to afford access to meta-tyrosine containing pacidamycin 4. Pictet-Spengler diversification of this compound using a small series of aryl-aldehydes was achieved with some derivatives affording remarkable diastereomeric control.

Antiproliferative activity of semisynthetic xylopic acid derivatives

Two ent-kaurene diterpenoids, ent-15-β-acetyloxy-kaur-16-en-19-oic acid (xylopic acid) 1 and ent-7-oxo-kaur-16-en-19-oic acid 2 were isolated from the fruits of Xylopia aethiopica. Chemical manipulation of xylopic acid yielded ent-kaurane derivatives 3, 4, 5, and 6. Their structures were elucidated by spectroscopic analysis, including 1 D- and 2 D-NMR spectroscopies. The antiproliferative activities of compounds 1, 2, 3, 4, and 6 were tested on breast MCF7 and SkBr3, endometrial Ishikawa, ovarian BG-1, mesothelioma IST-MES1 and hepatocellular HepG2 human tumor cells, and on mammalian MRC-10 fibroblast cells. Ketone 2 showed significant antiproliferative activity against MFC7 human breast cancer cells (IC₅₀ = 3 ± 1 µM) and A549 pulmonary adenocarcinoma (8 ± 1 µM), that was higher than the well-known anti-cancer agent cisplatin (IC₅₀ = 19 ± 3 and 15 ± 4 µM, respectively).

Semisynthetic Analogs of the Antibiotic Fidaxomicin-Design, Synthesis, and Biological Evaluation

The glycoslated macrocyclic antibiotic fidaxomicin (1, tiacumicin B, lipiarmycin A3) displays good to excellent activity against Gram-positive bacteria and was approved for the treatment of Clostridium difficile infections (CDI). Among the main limitations for this compound, its low water solubility impacts further clinical uses. We report on the synthesis of new fidaxomicin derivatives based on structural design and utilizing an operationally simple one-step protecting group-free preparative approach from the natural product. An increase in solubility of up to 25-fold with largely retained activity was observed. Furthermore, hybrid antibiotics were prepared that show improved antibiotic activities.

Semisynthetic Vitamin E Derivatives as Potent Antibacterial Agents against Resistant Gram-Positive Pathogens

New 5-substituted vitamin E derivatives were semisynthesized, and their antibacterial activity against human Gram-positive and Gram-negative pathogens was evaluated. Several vitamin E analogues were active against methicillin-resistant Staphylococcus aureus (MRSA) and/or methicillin-resistant Staphylococcus epidermidis (MRSE); structure-activity relationships (SARs) are discussed. As a result, it is shown that the presence of a carboxylic acid function at the C-5 position and/or at the end of the side chain is crucial for the antibacterial activity. The bactericidal or bacteriostatic action of three compounds against MRSA and MRSE was confirmed in a time-kill kinetics study, and the cytotoxicity on human cells was evaluated. The preliminary mechanism study by confocal microscopy indicated that those vitamin E analogues led to bacterial cell death through membrane disruption.

Scaffold Modifications in Erythromycin Macrolide Antibiotics. A Chemical Minireview

Clarithromycin and congeners are important antibacterial members of the erythromycin A 14-membered macrocyclic lactone family. The macrolide scaffold consists of a multifunctional core that carries both chemically reactive and non-reactive substituents and sites. Two main approaches are used in the preparation of the macrolides. In semisynthesis, the naturally occurring macrocycle serves as a substrate for structural modifications of peripheral substituents. This review is focused on substituents in non-activated positions. In the total synthesis approach, the macrolide antibiotics are constructed by a convergent assembly of building blocks from presynthesized substrates or substrates prepared by biogenetic engineering. The assembled block structures are linear chains that are cyclized by macrolactonization or by metal-promoted cross-coupling reactions to afford the 14-membered macrolactone. Pendant glycoside residues are introduced by stereoselective glycosylation with a donor complex. When available, a short summary of antibacterial MIC data is included in the presentations of the structural modifications discussed.

Synthesis of Novel Stilbene-Coumarin Derivatives and Antifungal Screening of Monotes kerstingii-Specialized Metabolites Against Fusarium oxysporum

Fusarium is one of the most toxigenic phytopathogens causing diseases and reduced agricultural productivity worldwide. Current chemical fungicides exhibit toxicity against non-target organisms, triggering negative environmental impact, and are a danger to consumers. In order to explore the chemical diversity of plants for potential antifungal applications, crude extract and fractions from Monotes kerstingii were screened for their activity against two multi-resistant Fusarium oxysporum strains: Fo32931 and Fo4287. Antifungal activity was evaluated by the determination of minimum inhibitory concentration (MIC) by broth dilution of fermentative yeasts using kinetic OD_{600 nm} reading by a spectrophotometer. The n-butanol fraction showed the best activity against Fo4287. We screened eleven previously reported natural compounds isolated from different fractions, and a stilbene-coumarin 5-[(1E)-2-(4-hydroxyphenyl)ethenyl]-4,7-dimethoxy-3-methyl-2H-1-benzopyran-2-one (1) was the most active compound against both strains. Compound 1 was employed as a nucleophile with a selection of electrophilic derivatizing agents to synthesize five novel stilbene-coumarin analogues. These semisynthetic derivatives showed moderate activity against Fo32931 with only prenylated derivative exhibiting activity comparable to the natural stilbene-coumarin (1), demonstrating the key role of the phenolic group.

Synthesis and insecticidal activity of sulfonate derivatives of sesamol against Mythimna separata in vivo

A series of sulfonate derivatives of sesamol were synthesized and evaluated for their insecticidal activity against a crop-threatening agricultural pest, the pre-third-instar larvae of Mythimna separata in vivo. Among all the target compounds, compounds 3b, 3g, 3h, and 3p exhibited more promising insecticidal activity than sesamol and toosendanin, and the final mortality rates (FMRs) of 3b, 3g, 3h, 3p, 1, and toosendanin were 60.7%/60.7%/67.9%/53.6%/32.1%/50.0%, respectively. Especially compound 3h exhibited the most potent insecticidal activity with FMRs of 67.9%. This suggested that a 4-fluorophenylsulfonyl group introduced at the hydroxyl position of sesamol was necessary for obtaining the most potent compound.[Formula: see text].

Semisynthetic Modification of Tau Protein with Di-Ubiquitin Chains for Aggregation Studies

Ubiquitin, a protein modifier that regulates diverse essential cellular processes, is also a component of the protein inclusions characteristic of many neurodegenerative disorders. In Alzheimer’s disease, the microtubule associated tau protein accumulates within damaged neurons in the form of cross-beta structured filaments. Both mono- and polyubiquitin were found linked to several lysine residues belonging to the region of tau protein that forms the structured core of the filaments. Thus, besides priming the substrate protein for proteasomal degradation, ubiquitin could also contribute to the assembly and stabilization of tau protein filaments. To advance our understanding of the impact of ubiquitination on tau protein aggregation and function, we applied disulfide-coupling chemistry to modify tau protein at position 353 with Lys48- or Lys63-linked di-ubiquitin, two representative polyubiquitin chains that differ in topology and structure. Aggregation kinetics experiments performed on these conjugates reveal that di-ubiquitination retards filament formation and perturbs the fibril elongation rate more than mono-ubiquitination. We further show that di-ubiquitination modulates tau-mediated microtubule assembly. The effects on tau protein aggregation and microtubule polymerization are essentially independent from polyubiquitin chain topology. Altogether, our findings provide novel insight into the consequences of ubiquitination on the functional activity and disease-related behavior of tau protein.

Synthesis of sulfonate derivatives of maltol and their biological activity against Phytophthora capsici and Bursaphelenchus xylophilus in vitro

Sixteen sulfonate derivatives of maltol were synthesized and screened in vitro for their anti-oomycete and nematicidal activity against Phytophthora capsici and Bursaphelenchus xylophilus, respectively. Among all the compounds, 3e, 3m, and 3p exhibited the most promising and pronounced anti-oomycete activity against P. capsici than zoxamide, and the EC₅₀ values of 25.42, 18.44, 23.69, and 27.99 mg/L, respectively; compounds 3e, 3m, 3n, and 3p exhibited potent nematicidal activity with LC₅₀ values ranging from 1 to 2 mg/L, especially 3m and 3n showed the best promising and pronounced nematicidal activity, with LC₅₀ values of 1.1762 and 1.2384 mg/L, respectively. [Formula: see text].

Recombinant Expression and Stapling of a Novel Long-Acting GLP-1R Peptide Agonist

Owing to their pleiotropic metabolic benefits, glucagon-like peptide-1 receptor (GLP-1R) agonists have been successfully utilized for treating metabolic diseases, such as type 2 diabetes and obesity. As part of our efforts in developing long-acting peptide therapeutics, we have previously reported a peptide engineering strategy that combines peptide side chain stapling with covalent integration of a serum protein-binding motif in a single step. Herein, we have used this strategy to develop a second generation extendin-4 analog rigidified with a symmetrical staple, which exhibits an excellent in vivo efficacy in an animal model of diabetes and obesity. To simplify the scale-up manufacturing of the lead GLP-1R agonist, a semisynthesis protocol was successfully developed, which involves recombinant expression of the linear peptide followed by attachment of a polyethylene glycol (PEG)-fatty acid staple in a subsequent chemical reaction step.

Isolation and identification of sapotexanthin 5,6-epoxide and 5,8-epoxide from red mamey (Pouteria sapota)

Two new carotenoids, sapotexanthin 5,6-epoxide and sapotexanthin 5,8-epoxide, have been isolated from the ripe fruits of red mamey (Pouteria sapota). Sapotexanthin 5,6-epoxide was also prepared by partial synthesis via epoxidation of sapotexanthin, and the (5R,6S) and (5S,6R) stereoisomers were identified by high-performance liquid chromatography-electronic circular dichroism (HPLC-ECD) analysis. Spectroscopic data of the natural and semisynthetic derivatives obtained by acid-catalyzed rearrangement of cryptocapsin 5,8-epoxide stereoisomers were compared for structural elucidation.

Analysis of Site-Specific Phosphorylation of PTEN by Using Enzyme-Catalyzed Expressed Protein Ligation

The activity and localization of PTEN, a tumor suppressor lipid phosphatase that converts the phospholipid PIP3 to PIP2, is governed in part by phosphorylation on a cluster of four Ser and Thr residues near the C terminus. Prior enzymatic characterization of the four monophosphorylated (1p) PTENs by using classical expressed protein ligation (EPL) was complicated by the inclusion of a non-native Cys at the ligation junction (aa379), which may alter the properties of the semisynthetic protein. Here, we apply subtiligase-mediated EPL to create wt 1p-PTENs. These PTENs are more autoinhibited than previously appreciated, consistent with the role of Tyr379 in driving autoinhibition. Alkaline phosphatase sensitivity analysis revealed that these autoinhibited 1p conformations are kinetically labile. In contrast to the Cys mutant 1p-PTENs, which are poorly recognized by an anti-phospho-PTEN antibody, three of the four wt 1p-PTENs are recognized by a commonly used anti-phospho-PTEN antibody.

Semisynthesis of the Neuroprotective Metabolite, Serofendic Acid

Serofendic acid is a natural neuroprotective molecule found in fetal calf serum. It is able to protect neurons against mechanisms of cell death associated with neurodegenerative disease. Because only trace quantities are present in fetal calf serum and complete chemical syntheses are long and inefficient, its development as a therapeutic agent has been slow. We engineered a heterologous metabolic pathway in Streptomyces to produce a late-stage synthetic intermediate, ent-atiserenoic acid, at high titers. We completed the total synthesis of serofendic acid from this intermediate in four steps.

Stereoselective synthesis of 4β-acyloxypodophyllotoxin derivatives as insecticidal agents

As our ongoing work on research of natural-product-based insecticidal agents, some 4α/β-acyloxypodophyllotoxin derivatives were synthesized, and were evaluated against the pre-third-instar larvae of B. mori, A. dissimilis and M. separate in vivo at the concentration of 1 mg ml^-1, respectively. Among all derivatives, compounds 2 g, h and 4c, d showed more promising insecticidal activities than their precursors - podophyllotoxin and epipodophyllotoxin. Furthermore, derivatives 2 g, h and 4c, d exhibited more relative amicable activities than their precursors - podophyllotoxin and epipodophyllotoxin. This results indicated that 4β-acyloxy moiety in the podophyllotoxin derivatives was significant for obtaining the more potent compounds.

Circumdatin-Aspyrone Conjugates from the Coral-Associated Aspergillus ochraceus LCJ11-102

Ochrazepines A-D (1-4), four new conjugates dimerized from 2-hydroxycircumdatin C (5) and aspyrone (6) by a nucleophilic addition to epoxide, were isolated from the fermentation broth of the coral-associated Aspergillus ochraceus strain LCJ11-102. Their structures including absolute configurations were determined based on spectroscopic analysis and chemical methods. Compounds 1-4 were also obtained by the semisynthesis from a nucleophilic addition of 2-hydroxycircumdatin C (5) to aspyrone (6). New compound 1 exhibited cytotoxic activity against 10 human cancer cell lines while new compounds 2 and 4 selectively inhibited U251 (human glioblastoma cell line) and compound 3 was active against A673 (human rhabdomyoma cell line), U87 (human glioblastoma cell line), and Hep3B (human liver cancer cell line) with IC₅₀ (half maximal inhibitory concentration) values of 2.5-11.3 μM among 26 tested human cancer cell lines.

A Review on Bioactivities of Tobacco Cembranoid Diterpenes

Cembranoids are carbocyclic diterpenes comprising four isoprene units and are natural products with a parent skeleton consisting of a 14-membered ring. They have gained wide interest in recent years and are a major hotspot in the research of natural product chemistry. Since 1962, various tobacco cembranoid diterpenes have been identified. This review systematically discusses and summarises the excellent antimicrobial, insecticidal, cytotoxic and neuroprotective activities of tobacco cembranoid diterpenes. These compounds show potential to be developed as botanical fungicides, cytotoxic drugs and drugs for the treatment of human immunodeficiency virus, Alzheimer's disease, Parkinson's disease, and other neurodegenerative diseases. However, there are relatively few studies on the structure⁻activity relationship (SAR) of tobacco cembranoid diterpenes. Therefore, future studies should focus on their structural modification, SAR and biogenic relationships.

9-Norlignans: Occurrence, Properties and Their Semisynthetic Preparation from Hydroxymatairesinol

Lignans, neolignans, norlignans and norneolignans constitute a large class of phenolic natural compounds. 9-Norlignans, here defined to contain a β⁻β' bond between the two phenylpropanoid units and to lack carbon number 9 from the parent lignan structure, are the most rarely occurring compounds within this class of natural compounds. We present here an overview of the structure, occurrence and biological activity of thirty-five 9-norlignans reported in the literature to date. In addition, we report the semisynthetic preparation of sixteen 9-norlignans using the natural lignan hydroxymatairesinol obtained from spruce knots, as starting material. 9-Norlignans are shown to exist in different species and to have various biological activities, and they may therefore serve as lead compounds for example for the development of anticancer agents. Hydroxymatairesinol is shown to be a readily available starting material for the preparation of norlignans of the imperanene, vitrofolal and noralashinol family.

Semisynthesis and Biological Evaluation of Platensimycin Analogues with Varying Aminobenzoic Acids

Platensimycin (PTM) is an excellent natural product drug lead against various gram-positive pathogens, including methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci. In this study, twenty PTM derivatives with varying aminobenzoic acids were semisynthesized. In contrast to all the previous reported inactive aminobenzaote analogues, a few of them showed moderate antibacterial activities against S. aureus. Our study suggested that modification of the conserved aminobenzoic acid remains a viable approach to diversify the PTM scaffold.

Bacterial Cell-Surface Display of Semisynthetic Cyclic Peptides

Semisynthetic cyclic peptides containing both non-proteinogenic building blocks, as the synthetic part, and a genetically encoded sequence amenable to DNA-based randomization hold great potential to expand the chemical space in the quest for novel bioactive peptides. Key to an efficient selection of novel binders to biomacromolecules is a robust method to link their genotype and phenotype. A novel bacterial cell surface display technology has been developed to present cyclic peptides composed of synthetic and genetically encoded fragments in their backbones. The fragments were combined by protein trans-splicing and intramolecular oxime ligation. To this end, a split intein half and an unnatural amino acid were displayed with the genetically encoded part on the surface of Escherichia coli. Addition of the synthetic fragment equipped with the split intein partner and an aminooxy moiety, as well as the application of a pH-shift protocol, resulted in the onsurface formation of the semisynthetic cyclic peptide. This approach will serve for the generation of cyclic peptide libraries suitable for selection by fluorescence-activated cell sorting, and more generally enables chemical modification of proteins on the bacterial surface.

Semisynthesis and absolute configuration of a novel rearranged 19,20-δ-lactone (9βH)-pimarane diterpene

Annonalide (3β,20-epoxy-3α,16-dihydroxy-15-oxo-7-pimaren-19,6β-olide, C₂₀H₂₆O₆, 1) is the major (9βH)-pimarane diterpene isolated from tubers of Cassimirella ampla, and it exhibits cytotoxic properties upon interaction with ctDNA. We have prepared new derivatives of 1 by modification of the (9βH)-pimarane backbone and report here the semisynthesis and absolute configuration of a novel rearranged 19,20-δ-lactone (9βH)-pimarane. Our approach was the reduction of the carbonyl groups of 1 with sodium borohydride, at positions C15 (no stereoselectivity) and C3 (stereoselective reduction), followed by rearrangement of the 6,19-γ-lactone ring into the six-membered 19,20-δ-lactone ring in 4a (3β,6β,16-trihydroxy-7-pimaren-19,20β-olide monohydrate, C₂₀H₃₀O₆·H₂O). The absolute structure of the new compound, 4a, was determined unambiguously with a Flack parameter x of -0.01 (11), supporting the stereochemistry assignment of 1 redetermined here. Besides the changes in the pattern of covalent bonds caused by reduction and lactone rearrangement, the conformation of one of the three fused cyclohexane rings is profoundly different in 4a, adopting a chair conformation instead of the boat shape found in 1. Furthermore, the intramolecular hydrogen bond present in 1 is lost in new compound 4a, due to hydrogen bonding between the 3-OH group and the solvent water molecule.

Lysine-14 acetylation of histone H3 in chromatin confers resistance to the deacetylase and demethylase activities of an epigenetic silencing complex

The core CoREST complex (LHC) contains histone deacetylase HDAC1 and histone demethylase LSD1 held together by the scaffold protein CoREST. Here, we analyze the purified LHC with modified peptide and reconstituted semisynthetic mononucleosome substrates. LHC demethylase activity toward methyl-Lys4 in histone H3 is strongly inhibited by H3 Lys14 acetylation, and this appears to be an intrinsic property of the LSD1 subunit. Moreover, the deacetylase selectivity of LHC unexpectedly shows a marked preference for H3 acetyl-Lys9 versus acetyl-Lys14 in nucleosome substrates but this selectivity is lost with isolated acetyl-Lys H3 protein. This diminished activity of LHC to Lys-14 deacetylation in nucleosomes is not merely due to steric accessibility based on the pattern of sensitivity of the LHC enzymatic complex to hydroxamic acid-mediated inhibition. Overall, these studies have revealed how a single Lys modification can confer a composite of resistance in chromatin to a key epigenetic enzyme complex involved in gene silencing.

Semisynthesis and Biological Evaluation of Oleanolic Acid 3-O-β-d-Glucuronopyranoside Derivatives for Protecting H9c2 Cardiomyoblasts against H₂O₂-Induced Injury

A series of novel oleanolic acid 3-O-β-d-glucuronopyranoside derivatives have been designed and synthesized. Biological evaluation has indicated that some of the synthesized compounds exhibit moderate to good activity against H₂O₂-induced injury in rat myocardial cells (H9c2). Particularly, derivative 28-N-isobutyl ursolic amide 3-O-β-d-galactopyranoside (8a) exhibited a greater protective effect than the positive control oleanolic acid 3-O-β-d-glucuronopyranoside, indicating that it possesses a great potential for further development as a cardiovascular disease modulator by structural modification.

A semisynthesis of 3'-O-ethyl-5,6-dihydrospinosyn J based on the spinosyn A aglycone

Spinetoram, a mixture of 3'-O-ethyl-5,6-dihydrospinosyn J (XDE-175-J, major component) and 3'-O-ethylspinosyn L (XDE-175-L, minor component), is a novel kind of green and efficient insecticide with a broad range of action against various insects. Nowadays, spinetoram is widely used in agriculture and food storage. This work reports a 7-step semisynthesis of 3'-O-ethyl-5,6-dihydrospinosyn J from spinosyn A aglycone. The C9-OH and C17-OH of the aglycone are successively connected to 3-O-ethyl-2,4-di-O-methylrhamnose and D-forosamine after selective protection and deprotection steps. Then, with 10% Pd/C as catalyst, the 5,6-double bond of the macrolide was selectively reduced to afford 3'-O-ethyl-5,6-dihydrospinosyn J. In addition, the 3-O-ethyl-2,4-di-O-methylrhamnose is synthesized from rhamnose which is available commercially, while the D-forosamine and aglycone are obtained via the hydrolysis of spinosyn A. High yields were obtained in each step, and all intermediates in the synthesis were characterized by 1H NMR, 13C NMR and MS techniques. This study can be helpful for developing an efficient chemical synthesis of spinetoram, and it also offers opportunities to synthesize spinosyn analogues and rhamnose derivatives.

Semisynthesis, an Anti-Inflammatory Effect of Derivatives of 1β-Hydroxy Alantolactone from Inula britannica

1β-hydroxy alantolactone, a sesquiterpene lactone mainly isolated from Inula genus plants, exhibits potent anti-inflammatory and anticancer activities. In this work, 1β-hydroxy alantolactone was isolated and five derivatives were prepared through different reactions at the C1-OH and C13-methylene motifs. The structure-activity relationships (SAR) of anti-inflammatory effects against NO production in RAW264.7 cells showed that the α-methylene-γ-butyrolactone motif was essential for NO production suppression and that retaining the C1-OH group can remarkably improve this effect. The NF-κB signaling pathway plays a pivotal role in the regulation of NO expression. Moreover, the levels of p65 and p50 phosphorylation were investigated and active compound 1 inhibited phosphorylation of p65 and p50 in TNF-α-induced NF-κB signaling. Further molecular docking suggested that 1 may target the p65 of NF-κB.

Discovery, semisynthesis, biological activities, and metabolism of ocotillol-type saponins

Ocotillol-type saponins are one kind of tetracyclic triterpenoids, sharing a tetrahydrofuran ring. Natural ocotillol-type saponins have been discovered in Panax quinquefolius L., Panax japonicus, Hana mina, and Vietnamese ginseng. In recent years, the semisynthesis of 20(S/R)-ocotillol-type saponins has been reported. The biological activities of ocotillol-type saponins include neuroprotective effect, antimyocardial ischemia, antiinflammatory, antibacterial, and antitumor activities. Owing to their chemical structure, pharmacological actions, and the stereoselective activity on antimyocardial ischemia, ocotillol-type saponins are subjected to extensive consideration. In this review, we sum up the discovery, semisynthesis, biological activities, and metabolism of ocotillol-type saponins.