Excelxylin A: a new seco A-ring tirucallane triterpenoid from the stem bark of Dysoxylum excelsum.

A new seco-A tirucallane triterpenoid named excelxylin A (1), along with two known seco-A triterpenoids (2-3), were isolated from the n-hexane extract of Dysoxylum excelsum (Spreng.) Blume ex G.Don stem bark. The structure and stereochemistry configuration of compounds 1-3 was established by NMR, IR, and HR-ESI-MS spectroscopic data analyses and comparison of their NMR data with literatures. The compounds exhibited the carbon framework for seco-A ring tirucallane triterpenoid, first reported in the Dysoxylum genus. All compounds were tested for their cytotoxicity against human cervical HeLa cells.

Limonoids from the fruits of Chisocheton lasiocarpus (Meliaceae).

Two new azadirone-type limonoids, namely lasiocarpine A (1) and lasiocarpine B (2) were isolated from the fruit of Chisocheton lasiocarpus along with three known limonoids (3-5). UV, IR, one- and two- dimensional NMR, and mass spectrometry were used to determine the chemical structure of the isolated compounds. Furthermore, their cytotoxic activity against breast cancer cell line MCF-7 was evaluated using PrestoBlue reagent. From these compounds, lasiocarpine A (1) showed the strongest activity with an IC50 value of 43.38 µM.

Tirucallane-type triterpenoid from the stem bark of Chisocheton lasiocarpus and its cytotoxic activity against MCF-7 breast cancer cells.

Chisocarpene A (1) is a new tirucallane-type triterpenoid together with odoratone (2) and 24-methylenecycloartanol (3), isolated from the stem bark of Chisocheton lasiocarpus. The chemical structures of compounds 1-3 were elucidated through a detailed analysis of their spectroscopic data (IR, MS, 1 D, and 2 D NMR). The isolated compounds were evaluated for cytotoxic activity against the MCF-7 breast cancer cell line using a resazurin-based assay. Compound 1 showed the most potent activity (IC50 26.56 ± 1.01 µM) and was two-fold more active than the positive control.

An Overview on Antimalarial Peptides: Natural Sources, Synthetic Methodology and Biological Properties.

Peptide compounds play a significant role in medicinal chemistry as they can inhibit the activity of species that cause malaria. This literature review summarizes the isolation of antimalarial peptides, the synthesis method with the detailed structure and sequences of each peptide, and discusses the biological activity of the isolated and synthesized compounds. The synthetic routes and reactions for cyclic and linear antimalarial peptides are systematically highlighted in this review including preparing building blocks, protection and deprotection, coupling and cyclization reactions until the target compound is obtained. Based on the literature data and the results, this review's aim is to provide information to discover and synthesize more antimalarial peptide for future research.

Epimerisation in Peptide Synthesis.

Epimerisation is basically a chemical conversion that includes the transformation of an epimer into another epimer or its chiral partner. Epimerisation of amino acid is a side reaction that sometimes happens during peptide synthesis. It became the most avoided reaction because the process affects the overall conformation of the molecule, eventually even altering the bioactivity of the peptide. Epimerised products have a high similarity of physical characteristics, thus making it difficult for them to be purified. In regards to amino acids, epimerisation is very important in keeping the chirality of the assembled amino acids unchanged during the peptide synthesis and obtaining the desirable product without any problematic purification. In this review, we report several factors that induce epimerisation during peptide synthesis, including how to characterise and affect the bioactivities. To avoid undesirable epimerisation, we also describe several methods of suppressing the process.

Synthesis of a Cyclooctapeptide, Cyclopurpuracin, and Evaluation of Its Antimicrobial Activity.

Cyclopurpuracin is a cyclooctapeptide isolated from the methanol extract of Annona purpurea seeds with a sequence of cyclo-Gly-Phe-Ile-Gly-Ser-Pro-Val-Pro. In our previous study, the cyclisation of linear cyclopurpuracin was problematic; however, the reversed version was successfully cyclised even though the NMR spectra revealed the presence of a mixture of conformers. Herein, we report the successful synthesis of cyclopurpuracin using a combination of solid- and solution-phase synthetic methods. Initially, two precursors of cyclopurpuracin were prepared, precursor linear A (NH2-Gly-Phe-Ile-Gly-Ser(t-Bu)-Pro-Val-Pro-OH) and precursor linear B (NH-Pro-Gly-Phe-Ile-Gly-Ser(t-Bu)-Pro-Val-OH, and various coupling reagents and solvents were trialled to achieve successful synthesis. The final product was obtained when precursors A and B were cyclised using the PyBOP/NaCl method, resulting in a cyclic product with overall yields of 3.2% and 3.6%, respectively. The synthetic products were characterised by HR-ToF-MS, 1H-NMR, and 13C-NMR, showing similar NMR profiles to the isolated product from nature and no conformer mixture. The antimicrobial activity of cyclopurpuracin was also evaluated for the first time against S. aureus, E. coli, and C. albicans, showing weak activity with MIC values of 1000 µg/mL for both synthetic products, whereas the reversed cyclopurpuracin was more effective with an MIC of 500 µg/mL.

New Triterpenoids from Lansium domesticum Corr. cv kokossan and Their Cytotoxic Activity.

Lansium domesticum Corr. is a member of the Meliaceae family that is widely spread in tropical and subtropical region of Asia and America. Traditionally, the fruit of this plant has been consumed because of its sweet taste. However, the fruit peels and the seeds of this plant have been rarely utilized. The previous chemical investigation of this plant showed the presence of secondary metabolites with many biological activities, including cytotoxic triterpenoid. Triterpenoids is a class of secondary metabolites which contain thirty carbon atoms in the main skeleton. The high modification of this type of compound, including the ring opening, highly oxygenated carbons, and the degradation of its carbon chain to give the nor-triterpenoid structure, is responsible for its cytotoxic activity. In this paper, we isolated and elucidated the chemical structure of two new onoceranoid triterpenes, kokosanolides E (1) and F (2), from the fruit peels of L. domesticum Corr., along with a new tetranortriterpenoid, kokosanolide G (3), from the seeds of L. domesticum Corr. The structural determination of compounds 1-3 was undertaken through FTIR spectroscopic analysis, 1D and 2D NMR, mass spectrometry, as well as through a comparison of the chemical shifts of the partial structures of compounds 1-3 with the literature data. The cytotoxic properties of compounds 1-3 were tested against MCF-7 breast cancer cells using the MTT assay. Moderate activity was shown by compounds 1 and 3, with IC50 values of 45.90 and 18.41 µg/mL, respectively, while compound 2 showed no activity (IC50 168.20 µg/mL). For the onoceranoid-type triterpene, the high symmetrical structure of compound 1 is presumably the reason for its better cytotoxic activity compared with that of compound 2. Compound 3 showed moderate activity, mainly because of the presence of the furan ring, which, based on the literature, gives better cytotoxic activity in a tetranortriterpenoid-type structure. The findings of three new triterpenoid compounds from L. domesticum indicate the significant value of this plant as a source of new compounds.

Resin Glycosides from Convolvulaceae Family: An Update.

Resin glycoside is a type of secondary metabolite isolated commonly from the Convolvulaceae family. It consists of oligosaccharides conjugated to organic acids with a larger percentage having a macrocyclic structure. The resin glycosides reported in this review is classified mostly based on the number of sugar units constructing the structure, which is correlated to the biological properties of the compounds. According to preliminary reviews, the protocols to isolate the compounds are not straightforward and require a special technique. Additionally, the structural determination of the isolated compounds needs to minimize the structure for the elucidation to become easier. Even though resin glycosides have a complicated structural skeleton, several total syntheses of the compounds have been reported in articles published from 2010 to date. This review is an update on the prior studies of the resin glycosides reported in 2010 and 2017. The review includes the classification, isolation techniques, structural determination, biological properties, and total synthesis of the resin glycosides.

Cyclic Peptides for the Treatment of Cancers: A Review.

Cyclic peptides have been widely reported to have therapeutic abilities in the treatment of cancer. This has been proven through in vitro and in vivo studies against breast, lung, liver, colon, and prostate cancers, among others. The multitude of data available in the literature supports the potential of cyclic peptides as anticancer agents. This review summarizes the findings from previously reported studies and discusses the different cyclic peptide compounds, the sources, and their modes of action as anticancer agents. The prospects and future of cyclic peptides will also be described to give an overview on the direction of cyclic peptide development for clinical applications.

Amino-Acid-Conjugated Natural Compounds: Aims, Designs and Results.

Protein is one of the essential macronutrients required by all living things. The breakdown of protein produces monomers known as amino acids. The concept of conjugating natural compounds with amino acids for therapeutic applications emerged from the fact that amino acids are important building blocks of life and are abundantly available; thus, a greater shift can result in structural modification, since amino acids contain a variety of sidechains. This review discusses the data available on amino acid-natural compound conjugates that were reported with respect to their backgrounds, the synthetic approach and their bioactivity. Several amino acid-natural compound conjugates have shown enhanced pharmacokinetic characteristics, including absorption and distribution properties, reduced toxicity and increased physiological effects. This approach could offer a potentially effective system of drug discovery that can enable the development of pharmacologically active and pharmacokinetically acceptable molecules.

Dammarane-Type Triterpenoid from the Stem Bark of Aglaia elliptica (Meliaceae) and Its Cytotoxic Activities.

Two new dammarane-type triterpenoid fatty acid ester derivatives, 3ß-oleate-20S-hydroxydammar-24-en (1) and 3ß-oleate-20S,24S-epoxy-25-hydroxydammarane (2) with a known dammarane-type triterpenoid compound, such as 20S-hydroxydammar-24-en-3-on (3), were isolated from the stem bark of Aglaiaelliptica (C.DC.) Blume. The chemical structures were determined by spectroscopic methods, including FTIR, NMR (one and two-dimensional), and HRESITOF-MS analysis, as well as chemical derivatization and comparison with previous literature. Furthermore, the synthetic analog resulting from transesterification of 1 and 2 also obtained 3ß,20S-dihydroxy-dammar-24-en (4) and 20S,24S-epoxy-3ß,25-dihydroxydammarane (5), respectively. The cytotoxic effect of all isolated and synthetic analog compounds was evaluated using PrestoBlue reagent against MCF-7 breast cancer cell and B16-F10 melanoma cell lines. The 20S-hydroxydammar-24-en-3-on (3) showed the strongest activity against MCF-7 breast cancer and B16-F10 melanoma cell, indicating that the ketone group at C-3 in 3 plays an essential role in the cytotoxicity of dammarane-type triterpenoid. On the other hand, compounds 1 and 2 had very weak cytotoxic activity against the two cell lines, indicating the presence of fatty acid, significantly decreasing cytotoxic activity. This showed the significance of the discovery to investigate the essential structural feature in dammarane-type triterpenoid, specifically for the future development of anticancer drugs.

ß-Resorcylic Acid Derivatives, with Their Phytotoxic Activities, from the Endophytic Fungus Lasiodiplodia theobromae in the Mangrove Plant Xylocarpus granatum.

Nine new ß-resorcylic acid derivatives, (15S)-de-O-methyllasiodiplodin (1), (13S,15S)-13-hydroxy-de-O-methyllasiodiplodin (2), (14S,15S)-14-hydroxy-de-O-methyllasiodiplodin (3), (13R,14S,15S)-13,14-dihydroxy-de-O-methyllasiodiplodin (4), ethyl (S)-2,4-dihydroxy-6-(8-hydroxynonyl)benzoate (5), ethyl 2,4-dihydroxy-6-(8-hydroxyheptyl)benzoate (6), ethyl 2,4-dihydroxy-6-(4-methoxycarbonylbutyl)benzoate (7), 3-(2-ethoxycarbonyl-3,5-dihydroxyphenyl)propionic acid (8), and isobutyl (S)-2,4-dihydroxy-6-(8-hydroxynonyl)benzoate (9), together with a known ethyl 2,4-dihydroxy-6-(8-oxononyl)benzoate (10) were obtained from Lasiodiplodia theobromae GC-22. The structures of these compounds were elucidated by extensive spectroscopic analyses. Compounds 1, 3, and 6 showed growth inhibitory effects against Digitaria ciliaris. Conversely, treatment with compounds 5, 6, 7, 9, and 10 stimulated elongation activity toward the root of Lactuca sativa. These data expand the repertoire of new ß-resorcylic acid derivatives that may function as lead compounds in the synthesis of new agrochemical agents.

Total synthesis of [ß-HIle]2-nodupetide: effect of ester to amide substitution on its antimicrobial activity.

The increasing prevalence of deaths due to multidrug-resistant bacteria (MDRB) in infectious disease therapy has become a global health concern. This led to the development of new antimicrobial therapeutic agents that can combat resistance to pathogenic bacteria. The utilization of natural peptide compounds as potential antimicrobial agents is very promising. Nodupetide, a cyclodepsipeptide with very strong antimicrobial activity against Pseudomonas aeruginosa was isolated from the fermentation of Nodulisporium sp. Unfortunately, one of its residues (3S,4S)-3-hydroxy-4-methylhexanoic acid (HMHA) is not commercially available and the synthesis strategies applied have not been successful. Hence, we synthesized its cyclopeptide analogue [ß-HIle]2-nodupetide by replacing HMHA with isoleucine homologue. A combination of solid- and solution-phase peptide synthesis was successfully carried out to synthesize [ß-HIle]2-nodupetide with an overall yield of 10.4%. The substitution of HMHA with ß-homoisoleucine (ß-HIle) changed the ester bond into an amide bond in nodupetide's backbone. The analogue was considerably inactive against Pseudomonas aeruginosa. It can be concluded that the ester bond is crucial for the antimicrobial activity of nodupetide.

Antioxidant and Antimicrobial Potential of Peptide from Rabbit Meat Hydrolysate Prepared by Trypsin and Zingibain.

<b>Background and Objective:</b> Rabbit meat is a livestock product potentially viable as a protein source to obtain peptides. Antioxidant and antimicrobial peptides are ingredients extracted from various foods through enzymatic hydrolysis, chemical hydrolysis and fermentation to produce health-promoting foods. This research aims to investigate the potential of rabbit meat as a source of antioxidant and antimicrobial peptides through hydrolysis using trypsin and zingibain enzymes. <b>Materials and Methods:</b> This research conducted an explorative-descriptive approach, focusing on antioxidant and antimicrobial activity. Rabbit meat was extracted using trypsin, zingibain and a combination of trypsin and crude extract zingibain. The hydrolyzed rabbit meat extract was tested at intervals of 0, 2, 6, 16, 24, 40 and 48 hrs to determine the degree of hydrolysis and the profile of hydrolyzed proteins with electrophoresis SDS PAGE. The antioxidant activity was tested using the DPPH method and the antimicrobial activity using agar well diffusion method. <b>Results:</b> The degree of hydrolysis increased with the hydrolysis time. The highest protein content of rabbit meat extract hydrolyzed with trypsin was 287.65 mg/mL, observed during 12 hrs hydrolysis. The optimum conditions for the hydrolysis of rabbit meat protein were obtained at 24 hrs, with an IC₅₀ value of 52.45% hydrolyzed by trypsin. As per antimicrobial activities, <i>Escherichia coli</i> and <i>Salmonella</i> sp. were more effective in inhibiting rabbit meat hydrolysates compared to <i>Pseudomonas aeruginosa</i> and <i>Staphylococcus aureus</i>. The inhibition of all pathogen increased until 12 hrs hydrolysis but decreased in 24 hrs hydrolysis. <b>Conclusion:</b> The combination zingibain enzyme and trypsin is feasible for hydrolyzing rabbit meat and the optimum hydrolysis time was 24 hrs with IC₅₀ 52.45 ppm, although accompanied by reduction in antibacterial activities.

Computational studies and synthesis of 131iodine-labeled nocardiotide A analogs as a peptide-based theragnostic radiopharmaceutical ligand for cancer targeting SSTR2.

Radiolabeled peptides belong to a highly specific group of radiotracers used in oncology, particularly for diagnostics and cancer therapy. With the notable advantages of high binding affinity and selectivity to cancer cells, they have proven to be very useful in nuclear medicine. As a result, efforts have been focused on discovering new peptide sequences for radiopeptide preparation. Nocardiotide A, a cyclic hexapeptide comprising the amino acids cyclo-Trp-Ile-Trp-Leu-Val-Ala (cWIWLVA) isolated from Nocardiopsis sp., has shown significant cytotoxicity against cancer cells, rendering it a suitable candidate for the process. Therefore, the present study aimed to design a stable and effective radiopeptide by labeling nocardiotide A with iodine-131 (131I), ensuring that its affinity to SSTR2 is not compromised. In silico study showed that structural modification of nocardiotide A labeled with 131iodine exhibited good affinity value, forming hydrogen bonds with key residues, such as Q.102 and T.194, which are essential in SSTR2. Based on the results, cyclic hexapeptides of cWIWLYA were selected for further synthesis, and its peptide product was confirmed by the presence of an ionic molecule peak m/z [M + Na]+ 855.4332 (yield, 25.60%). In vitro tests conducted on cWIWLYA showed that cWIWLYA can bind to HeLa cancer cells. Radiopeptide synthesis was initiated with radiolabeling of cWIWLYA by 131I using the chloramine-T method that showed a radiochemical yield of 93.37%. Non-radioactive iodine labeling reaction showed that iodination was successful, which detected the presence of di-iodinated peptide (I2-cWIWLYA) with m/z [M + Na]+ 1107.1138. In summary, a radiopeptide derived from nocardiotide A showed great potential for further development as a diagnostic and therapeutic agent in cancer treatment.

Correction: Synthesis and anticancer evaluation of [d-Ala]-nocardiotide A.

[This corrects the article DOI: 10.1039/D4RA00025K.].

Synthesis and anticancer evaluation of [d-Ala]-nocardiotide A.

Cancer is currently one of the biggest causes of death in the world. Like some microorganisms, cancer cells also develop resistance to various chemotherapy drugs and are termed multidrug resistant (MDR). In this regard, there is a need to develop new alternative anticancer agents. Anticancer peptides (ACPs) with high selectivity and high cell penetration ability are a promising candidate, as well as they are easy to modify. A cyclohexapeptide called nocardiotide A was isolated from the marine sponge Callyspongia sp., which is cytotoxic towards several cancer cells such as MM, 1S, HeLa, and CT26 cells. Previously, nocardiotide A was synthesized with a very low yield owing to its challenging cyclization process. In this study, we synthesized [d-Ala]-nocardiotide A as a derivative of nocardiotide A using a combination of solid phase peptide synthesis (SPPS) and liquid phase peptide synthesis (LPPS). The synthesis was carried out by selecting a d-alanine residue at the C-terminus to give a desired cyclic peptide product with a yield of 31% after purification. The purified [d-Ala]-nocardiotide A was characterized using HR-ToF MS and 1H and 13C-NMR spectroscopy to validate the desired product. The anticancer activity of the peptide was determined against HeLa cancer cell lines with an IC50 value of 52 µM compared to the parent nocardiotide A with an IC50 value of 59 µM. In the future, we aim to mutate various l-amino acids in nocardiotide A to d-amino acids to prepare nocardiotide A derivatives with a higher activity to kill cancer cells with higher membrane permeation. In addition, the mechanism of action of nocardiotide A and its derivatives will be evaluated.

Paraxylines A-G: Highly oxygenated preurianin-type limonoids with immunomodulatory TLR4 and cytotoxic activities from the stem bark of Dysoxylum parasiticum.

Seven previously undescribed preurianin-type limonoids, namely paraxylines A-G, and three known analogs were isolated from stem bark of Dysoxylum parasiticum. The structures, including absolute configurations, were established through spectroscopic analyses, quantum chemical calculations using the density functional theory method, as well as the DP4+ algorithm. Paraxylines A-G were identified as the first preurianin-type with full substitution at C, D-rings, leading to the highly oxygenated seco-limonoids skeleton. The secreted alkaline phosphate assay against an engineered human and murine TLR4 of HEK-Blue cells was performed to evaluate the immune regulating effects. Among them, paraxyline B was found to be a remarkable TLR4 agonist whereas two analogs (toonapubesins A and B) were found to antagonise lipopolysaccharide stimulation of the TLR4 pathway. Paraxylines A and C-E acted either as agonists or antagonists depending on the origin of the TLR4 receptor (human or mouse). The effect of these selected compounds on the expression of pro-inflammatory cytokines TNF-α, IL-1α, IL-1ß, and IL-6 of the NF-κB signaling pathway were examined in macrophage cell lines, revealing dose-dependent effects. Additionally, paraxylines A, C, D, and G also presented modest cytotoxic activity against MCF-7 and HeLa cell lines with IC50 values ranging from 23.1 to 43.5 µM.

The 2,3-epoxy naphthoquinol produced by endophyte Arthrinium marii M-211.

A novel 2,3-epoxy naphthoquinol, named (6R,7R,8R)-theissenone A (1), possessing an oxatricyclo[5.4.0.03,5]undeca-trien-2-one skeleton, together with two known compounds, (6S,7R,8R)-theissenone (2) and arthrinone (3), were produced by an endophytic fungus, Arthrinium marii M-211, which was isolated from mangrove plants. The structure of 1, including the absolute stereochemistry, was elucidated by analysis of nuclear magnetic resonance (NMR) and mass spectrometry (MS) data and time-dependent density functional theory (TDDFT) calculations of electronic circular dichroism (ECD) spectra. Additionally, the absolute structure of 2 was deduced as a diastereomer of 1 using ECD spectral data analysis. Compounds 1, 2 and 3 exhibited cytotoxic activity against the H4IIE rat hepatoma cells, with IC50 values of 67.5, 46.6 and 13.4 µM, respectively.

Dysoticans F-H: three unprecedented dimeric cadinanes from Dysoxylum parasiticum (Osbeck) Kosterm. stem bark.

An asymmetrical true-dimeric cadinane via ketonic bridge [C-15/C-3'], dysotican F (1), two symmetrical pseudo-cadinane dimers through an O-ether linkage [C-3/C-3'], dysoticans G (2) and H (3), as well as three known sesquiterpenoids 4-6 were obtained from the stem bark of Dysoxylum parasiticum (Osbeck) Kosterm. (Meliaceae). Their structures were determined by spectroscopic and quantum chemical calculations of 13C NMR shifts using a GIAO method and electronic circular dichroism (ECD) using a TDDFT method. A possible biogenetic pathway for 1-3 beginning from the known compounds (i-ii) was proposed. Cytotoxic evaluation showed that 2 as a new lead compound is the most potent against the MCF-7 and HeLa cell lines with IC50 values of 12.07 ± 0.17 µM and 9.29 ± 0.33 µM, while 1 has moderate inhibition with IC50 values of 31.59 ± 0.34 µM and 27.93 ± 0.25 µM. Furthermore, 3 is a selective inhibitor against the HeLa cell growth with an IC50 value of 39.72 ± 0.18 µM. A brief structure-activity relationship analysis of all isolated compounds 1-6 was also provided, including comparison with the coexisting molecules in the previous report.