Discovery, absolute assignments, and total synthesis of asperversiamides A-C and their potent activity against Mycobacterium marinum

Medium-sized peptides from microbial sources with potential for antibacterial drug development

Covering: 1993 to the end of 2022As the rapid development of antibiotic resistance shrinks the number of clinically available antibiotics, there is an urgent need for novel options to fill the existing antibiotic pipeline. In recent years, antimicrobial peptides have attracted increased interest due to their impressive broad-spectrum antimicrobial activity and low probability of antibiotic resistance. However, macromolecular antimicrobial peptides of plant and animal origin face obstacles in antibiotic development because of their extremely short elimination half-life and poor chemical stability. Herein, we focus on medium-sized antibacterial peptides (MAPs) of microbial origin with molecular weights below 2000 Da. The low molecular weight is not sufficient to form complex protein conformations and is also associated to a better chemical stability and easier modifications. Microbially-produced peptides are often composed of a variety of non-protein amino acids and terminal modifications, which contribute to improving the elimination half-life of compounds. Therefore, MAPs have great potential for drug discovery and are likely to become key players in the development of next-generation antibiotics. In this review, we provide a detailed exploration of the modes of action demonstrated by 45 MAPs and offer a concise summary of the structure-activity relationships observed in these MAPs.

Bioactivities of natural product geodin congeners and their preliminary structure activity relationship

A series of 6 novel ester derivatives 2-7 of natural product geodin 1 were designed and semi-synthesized through one mild step reaction with high yield. Compounds 2-7 showed strong inhibitory activities against Staphylococcus aureus in the range of 2.35-9.41 μM. Compounds 4 and 7 showed very strong inhibitory activities against antifouling bacteria Aeromonas salmonicida with MICs of 2.42 μM and 4.56 μM respectively. Most notably compounds 3-7 showed potent antifungal activities against Candida albicans in the range of 0.59-2.44 μM. Particularly, compound 3 showed the highest antifungal activity against C. albicans with a MIC value of 0.59 μM. The preliminary structure activity relationship of these derivatives showed that replacement of 4-OH group with benzoyl substituents could enhance the antibacterial and antifungal activities of geodin 1.

Recent Advances in Polypeptide Antibiotics Derived from Marine Microorganisms

In the post-antibiotic era, the rapid development of antibiotic resistance and the shortage of available antibiotics are triggering a new health-care crisis. The discovery of novel and potent antibiotics to extend the antibiotic pipeline is urgent. Small-molecule antimicrobial peptides have a wide variety of antimicrobial spectra and multiple innovative antimicrobial mechanisms due to their rich structural diversity. Consequently, they have become a new research hotspot and are considered to be promising candidates for next-generation antibiotics. Therefore, we have compiled a collection of small-molecule antimicrobial peptides derived from marine microorganisms from the last fifteen years to show the recent advances in this field. We categorize these compounds into three classes-cyclic oligopeptides, cyclic depsipeptides, and cyclic lipopeptides-according to their structural features, and present their sources, structures, and antimicrobial spectrums, with a discussion of the structure activity relationships and mechanisms of action of some compounds.

Peptides from Marine-Derived Fungi: Chemistry and Biological Activities

Marine natural products are well-recognized as potential resources to fill the pipeline of drug leads to enter the pharmaceutical industry. In this circumstance, marine-derived fungi are one of the unique sources of bioactive secondary metabolites due to their capacity to produce diverse polyketides and peptides with unique structures and diverse biological activities. The present review covers the peptides from marine-derived fungi reported from the literature published from January 1991 to June 2023, and various scientific databases, including Elsevier, ACS publications, Taylor and Francis, Wiley Online Library, MDPI, Springer, Thieme, Bentham, ProQuest, and the Marine Pharmacology website, are used for a literature search. This review focuses on chemical characteristics, sources, and biological and pharmacological activities of 366 marine fungal peptides belonging to various classes, such as linear, cyclic, and depsipeptides. Among 30 marine-derived fungal genera, isolated from marine macro-organisms such as marine algae, sponges, coral, and mangrove plants, as well as deep sea sediments, species of Aspergillus were found to produce the highest number of peptides (174 peptides), followed by Penicillium (23 peptides), Acremonium (22 peptides), Eurotium (18 peptides), Trichoderma (18 peptides), Simplicillium (17 peptides), and Beauveria (12 peptides). The cytotoxic activity against a broad spectrum of human cancer cell lines was the predominant biological activity of the reported marine peptides (32%), whereas antibacterial, antifungal, antiviral, anti-inflammatory, and various enzyme inhibition activities ranged from 7% to 20%. In the first part of this review, the chemistry of marine peptides is discussed and followed by their biological activity.

Natural products and their analogues acting against Mycobacterium tuberculosis: A recent update

Tuberculosis (TB) remains one of the deadliest infectious diseases caused by Mycobacterium tuberculosis (M.tb). It is responsible for significant causes of mortality and morbidity worldwide. M.tb possesses robust defense mechanisms against most antibiotic drugs and host responses due to their complex cell membranes with unique lipid molecules. Thus, the efficacy of existing front-line drugs is diminishing, and new and recurring cases of TB arising from multidrug-resistant M.tb are increasing. TB begs the scientific community to explore novel therapeutic avenues. A precise knowledge of the compounds with their mode of action could aid in developing new anti-TB agents that can kill latent and actively multiplying M.tb. This can help in the shortening of the anti-TB regimen and can improve the outcome of treatment strategies. Natural products have contributed several antibiotics for TB treatment. The sources of anti-TB drugs/inhibitors discussed in this work are target-based identification/cell-based and phenotypic screening from natural products. Some of the recently identified natural products derived leads have reached clinical stages of TB drug development, which include rifapentine, CPZEN-45, spectinamide-1599 and 1810. We believe these anti-TB agents could emerge as superior therapeutic compounds to treat TB over known Food and Drug Administration drugs.

Sulfur-containing marine natural products as leads for drug discovery and development

Among the large series of marine natural products (MNPs), sulfur-containing MNPs have emerged as potential therapeutic agents for the treatment of a range of diseases. Herein, we reviewed 95 new sulfur-containing MNPs isolated during the period between 2021 and March 2023. In addition, we discuss that the widely used strategies and the emerging technologies including natural product-based antibody drug conjugates (ADCs), small-molecule-based proteolysis targeting chimeras (PROTACs), nanotechnology-based drug carriers, artificial intelligence (AI)-driven drug discovery have been used for improving the efficiency and success rate of NP-based drug development. We also provide perspectives regarding the challenges and opportunities in sulfur-containing MNPs based drug discovery and development and future research directions.

Targeted isolation of antitubercular cycloheptapeptides and an unusual pyrroloindoline-containing new analog, asperpyrroindotide A, using LC-MS/MS-based molecular networking

Further insights on the secondary metabolites of a soft coral-derived fungus Aspergillus versicolor under the guidance of MS/MS-based molecular networking led to the isolation of seven known cycloheptapeptides, namely, asperversiamides A-C (1-3) and asperheptatides A-D (4-7) and an unusual pyrroloindoline-containing new cycloheptapeptide, asperpyrroindotide A (8). The structure of 8 was elucidated by comprehensive spectroscopic data analysis, and its absolute configuration was determined by advanced Marfey's method. The semisynthetic transformation of 1 into 8 was successfully achieved and the reaction conditions were optimized. Additionally, a series of new derivatives (10-19) of asperversiamide A (1) was semi-synthesized and their anti-tubercular activities were evaluated against Mycobacterium tuberculosis H37Ra. The preliminary structure-activity relationships revealed that the serine hydroxy groups and the tryptophan residue are important to the activity.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s42995-022-00157-8.

Discovery, total syntheses and potent anti-inflammatory activity of pyrrolinone-fused benzoazepine alkaloids Asperazepanones A and B from Aspergillus candidus

Natural products are well established as an important resource and play an important role in drug discovery. Here, two pyrrolinone-fused benzoazepine alkaloids, (+)-asperazepanones A (1) and B (2) with a 6/7/5 ring system, together with the artifact (-)-asperazepanone A (1), were isolated from the coral-derived Aspergillus candidus fungus. Their structures including absolute configurations were elucidated by extensive spectroscopic methods, single crystal X-ray diffraction, and ECD calculations. Furthermore, total syntheses of (±)-1 and (±)-2 have been achieved starting from the commercially L-aspartic acid diethyl ester hydrochloride and monoethyl malonate in 7 and 8 steps, respectively. The key step in the syntheses was an intramolecular Friedel-Crafts reaction to build the unique tricyclic skeleton. Interestingly, (+)-2 not only showed obviously inhibitory activity against NO production, but also inhibited potent LPS-induced expression of TNF-α and IL-6 at the concentration of 0.1 μM. It thus represents a potentially promising lead for anti-inflammatory drug discovery.

Boosting physical-mechanical properties of adipic acid/chitosan films by DMTMM cross-linking

In this paper we present a novel strategy to easily prepare biodegradable chitosan derived films as new packaging systems. Combination of chitosan, adipic acid and 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methyl-morpholinium chloride (DMTMM) allowed to obtain high-performing cross-linked films. Biobased glycerol was employed as plasticizer. An in-depth study was performed on ten different samples in order to evaluate the role of DMTMM as cross-linking agent. Experimental data showed that 15 wt% of DMTMM enhanced moisture content and moisture uptake (10.42% and 11.11%), water vapor permeability (0.13 10^-7 g m^-1 h^-1 Pa^-1) and good UV barrier properties. Additionally, 30 wt% of DMTMM significantly increased the tensile strength of films up to 83 MPa and elongation at break values reached 39.7%. Thermogravimetric, IR, XRD and SEM analysis confirmed that physical-mechanical properties of the obtained films were considerably improved, due to cross-linking by DMTMM, demonstrating promising properties for packaging applications.

Fungal-derived compounds and mycogenic nanoparticles with antimycobacterial activity: a review

Tuberculosis (TB) is a persistent lung infection caused by Mycobacterium tuberculosis. The disease is characterized by high mortality rates of over 1 million per year. Unfortunately, the potency and effectiveness of currently used anti-TB drugs is gradually decreasing due to the constant development of persistence and resistance by M. tuberculosis. The adverse side effects associated with current anti-TB drugs, along with anti-TB drug resistance, present an opportunity to bio-prospect novel potent anti-TB drugs from unique sources. Fundamentally, fungi are a rich source of bioactive secondary metabolites with valuable therapeutic potential. Enhancing the potency and effectiveness of fungal-based anti-TB drug leads by chemical synthesis and/or modification with nanomaterials, may result in the discovery of novel anti-TB drugs. In this review, the antimycobacterial activity of fungal-derived compounds and mycogenic nanoparticles are summarized. Numerous fungal-derived compounds as well as some mycogenic nanoparticles that exhibit strong antimycobacterial activity that is comparable to that of approved drugs, were found. If fully explored, fungi holds the promise to become key drivers in the generation of lead compounds in TB-drug discovery initiatives.

Design, Semisynthesis, Insecticidal and Antibacterial Activities of a Series of Marine-Derived Geodin Derivatives and Their Preliminary Structure–Activity Relationships

To enhance the biological activity of the natural product geodin (1), isolated from the marine-derived fungus Aspergillus sp., a series of new ether derivatives (2–37) was designed and semisynthesized using a high-yielding one-step reaction. In addition, the insecticidal and antibacterial activities of all geodin congeners were evaluated systematically. Most of these derivatives showed better insecticidal activities against Helicoverpa armigera Hübner than 1. In particular, 15 showed potent insecticidal activity with an IC50 value of 89 μM, comparable to the positive control azadirachtin (IC50 = 70 μM). Additionally, 5, 12, 13, 16, 30 and 33 showed strong antibacterial activity against Staphylococcus aureus and Aeromonas salmonicida with MIC values in the range of 1.15–4.93 μM. The preliminary structure–activity relationships indicated that the introduction of halogenated benzyl especially fluorobenzyl, into 1 and substitution of 4-OH could be key factors in increasing the insecticidal and antibacterial activities of geodin.

Semi-Synthesis, Cytotoxic Evaluation, and Structure-Activity Relationships of Brefeldin A Derivatives with Antileukemia Activity

Brefeldin A (1), a potent cytotoxic natural macrolactone, was produced by the marine fungus Penicillium sp. (HS-N-29) from the medicinal mangrove Acanthus ilicifolius. Series of its ester derivatives 2-16 were designed and semi-synthesized, and their structures were characterized by spectroscopic methods. Their cytotoxic activities were evaluated against human chronic myelogenous leukemia K562 cell line in vitro, and the preliminary structure-activity relationships revealed that the hydroxy group played an important role. Moreover, the monoester derivatives exhibited stronger cytotoxic activity than the diester derivatives. Among them, brefeldin A 7-O-2-chloro-4,5-difluorobenzoate (7) exhibited the strongest inhibitory effect on the proliferation of K562 cells with an IC50 value of 0.84 µM. Further evaluations indicated that 7 induced cell cycle arrest, stimulated cell apoptosis, inhibited phosphorylation of BCR-ABL, and thereby inactivated its downstream AKT signaling pathway. The expression of downstream signaling molecules in the AKT pathway, including mTOR and p70S6K, was also attenuated after 7-treatment in a dose-dependent manner. Furthermore, molecular modeling of 7 docked into 1 binding site of an ARF1-GDP-GEF complex represented well-tolerance. Taken together, 7 had the potential to be served as an effective antileukemia agent or lead compound for further exploration.

Marine Indole Alkaloids-Isolation, Structure and Bioactivities

Indole alkaloids are heterocyclic natural products with extensive pharmacological activities. As an important source of lead compounds, many clinical drugs have been derived from natural indole compounds. Marine indole alkaloids, from unique marine environments with high pressure, high salt and low temperature, exhibit structural diversity with various bioactivities, which attracts the attention of drug researchers. This article is a continuation of the previous two comprehensive reviews and covers the literature on marine indole alkaloids published from 2015 to 2021, with 472 new or structure-revised compounds categorized by sources into marine microorganisms, invertebrates, and plant-derived. The structures and bioactivities demonstrated in this article will benefit the synthesis and pharmacological activity study for marine indole alkaloids on their way to clinical drugs.

The intriguing chemistry and biology of sulfur-containing natural products from marine microorganisms (1987-2020)

Natural products derived from marine microorganisms have received great attention as a potential resource of new compound entities for drug discovery. The unique marine environment brings us a large group of sulfur-containing natural products with abundant biological functionality including antitumor, antibiotic, anti-inflammatory and antiviral activities. We reviewed all the 484 sulfur-containing natural products (non-sulfated) isolated from marine microorganisms, of which 59.9% are thioethers, 29.8% are thiazole/thiazoline-containing compounds and 10.3% are sulfoxides, sulfones, thioesters and many others. A selection of 133 compounds was further discussed on their structure-activity relationships, mechanisms of action, biosynthesis, and druggability. This is the first systematic review on sulfur-containing natural products from marine microorganisms conducted from January 1987, when the first one was reported, to December 2020.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-021-00101-2.

Cytochalasans and azaphilones: suitable chemotaxonomic markers for the Chaetomium species

The accurate taxonomic concept of the fungal Chaetomium species has been a hard work due to morphological similarity. Chemotaxonomy based on secondary metabolites is a powerful tool for taxonomical purposes, which could be used as an auxiliary reference to solve the problems encountered in the classification of Chaetomium. Among secondary metabolites produced by Chaetomium, cytochalasans and azaphilones exhibited a pattern of distribution and frequency of occurrence that establish them as chemotaxonomic markers for the Chaetomium species. This review attempted to elucidate the composition of the Chaetomium species and its relationship with classical taxonomy by summarizing the pattern of cytochalasans and azaphilones distribution and biosynthesis in the Chaetomium species. KEY POINTS: • Secondary metabolites from the genus Chaetomium are summarized. • Cytochalasans and azaphilones could be characteristic metabolites of the Chaetomium species. • Cytochalasans and azaphilones could be used to analyze for taxonomical purposes.

Discovery of penipanoid C-inspired 2-(3,4,5-trimethoxybenzoyl)quinazolin-4(3H)-one derivatives as potential anticancer agents by inhibiting cell proliferation and inducing apoptosis in hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC) is the most common form of liver cancer and the fourth leading cause of cancer-related death worldwide. First-line drugs such as sorafenib provide only a modest benefit to HCC patients. In this study, the gram-scale synthesis of 2-benzoylquinazolin-4(3H)-one skeleton was achieved successfully via the I₂/DMSO catalytic system. A series of penipanoid C-inspired 2-(3,4,5-trimethoxybenzoyl)quinazolin-4(3H)-one derivatives was synthesized and evaluated for their cytotoxic activities against four cancer cell lines, HepG2, Bel-7402, A549, and U251. Among these compounds, 4a was the most effective one with IC₅₀ values of 1.22 μM and 1.71 μM against HepG2 and Bel-7402 cells, respectively. Mechanistic studies showed that 4a inhibited hepatocellular carcinoma cell proliferation via arresting cell cycle. Additionally, 4a induced HepG2 cells apoptosis by inducing reactive oxygen species production and elevating the expression of apoptosis-related proteins. More importantly, 4a displayed significant in vivo anticancer effects in the HepG2 xenograft models. This suggests that 4a is a promising lead compound with the potential to be developed as a chemotherapy agent for hepatocellular carcinoma.

Efficient Triazine Derivatives for Collagenous Materials Stabilization

Nowadays, the need to reduce plastic waste and scantly biodegradable fossil-based products is of great importance. The use of leather as an alternative to synthetic materials is gaining renewed interest, but it is fundamental that any alternative to plastic-based materials should not generate an additional environmental burden. In the present work, a simple protocol for collagen stabilization mediated by 2-chloro-4,6-diethoxy-1,3,5-triazine (CDET) and a tert-amine has been described. Different tert-amines were tested in combination with CDET in a standard amidation reaction between 2-phenylethylamine and benzoic acid. Best performing condensation systems have been further tested for the cross-linking of both collagen powder and calf hides. The best results were achieved with CDET/NMM giving high-quality leather with improved environmental performances.

Nitrogenous Compounds from the Antarctic Fungus Pseudogymnoascus sp. HSX2#-11

The species Pseudogymnoascus is known as a psychrophilic pathogenic fungus which is ubiquitously distributed in Antarctica. While the studies of its secondary metabolites are infrequent. Systematic research of the metabolites of the Antarctic fungus Pseudogymnoascus sp. HSX2#-11 led to the isolation of one new pyridine derivative, 4-(2-methoxycarbonyl-ethyl)-pyridine-2-carboxylic acid methyl ester (1), together with one pyrimidine, thymine (2), and eight diketopiperazines, cyclo-(dehydroAla-l-Val) (3), cyclo-(dehydroAla-l-Ile) (4), cyclo-(dehydroAla-l-Leu) (5), cyclo-(dehydroAla-l-Phe) (6), cyclo-(l-Val-l-Phe) (7), cyclo-(l-Leu-l-Phe) (8), cyclo-(l-Trp-l-Ile) (9) and cyclo-(l-Trp-l-Phe) (10). The structures of these compounds were established by extensive spectroscopic investigation, as well as by detailed comparison with literature data. This is the first report to discover pyridine, pyrimidine and diketopiperazines from the genus of Pseudogymnoascus.

17-Hydroxybrevianamide N and Its N1-Methyl Derivative, Quinazolinones from a Soft-Coral-Derived Aspergillus sp. Fungus: 13S Enantiomers as the True Natural Products

Under the guidance of MS/MS-based molecular networking and HPLC-UV, two new alkaloid racemates, (±)-17-hydroxybrevianamide N (1) and (±)-N1-methyl-17-hydroxybrevianamide N (2), featuring a rare o-hydroxyphenylalanine residue and an imide subunit, were isolated from a soft-coral-derived Aspergillus sp. fungus. The true natural products (+)-1 and (+)-2 were further monitored and obtained from the freshly prepared EtOAc extracts, while (-)-1 and (-)-2 are artifacts generated during extraction and purification processes. Simultaneously, the structures including absolute configurations of (+)-13S-1, (-)-13R-1, (+)-13S-2, and (-)-13R-2 were elucidated on the basis of comprehensive spectroscopic analysis, ECD calculations, and X-ray diffraction data. Interestingly, basic solution promotes the racemization of (+)-1 and (-)-1, whereas acidic solution suppresses the transformation. The current research was concerned with the true natural products and their artifacts, providing critical insight into the isolation and identification of natural products.

Targeted Isolation of Asperheptatides from a Coral-Derived Fungus Using LC-MS/MS-Based Molecular Networking and Antitubercular Activities of Modified Cinnamate Derivatives

Under the guidance of MS/MS-based molecular networking, four new cycloheptapeptides, namely, asperheptatides A-D (1-4), were isolated together with three known analogues, asperversiamide A-C (5-7), from the coral-derived fungus Aspergillus versicolor. The planar structures of the two major compounds, asperheptatides A and B (1 and 2), were determined by comprehensive spectroscopic data analysis. The absolute configurations of the amino acid residues were determined by advanced Marfey's method. The two structurally related trace metabolites, asperheptatides C and D (3 and 4), were characterized by ESI-MS/MS fragmentation methods. A series of new derivatives (8-26) of asperversiamide A (5) were semisynthesized. The antitubercular activities of 1, 2, and 5-26 against Mycobacterium tuberculosis H37Ra were also evaluated. Compounds 9, 13, 23, and 24 showed moderate activities with MIC values of 12.5 μM, representing a potential new class of antitubercular agents.

Sustainable Triazine-Based Dehydro-Condensation Agents for Amide Synthesis

Conventional methods employed today for the synthesis of amides often lack of economic and environmental sustainability. Triazine-derived quaternary ammonium salts, e.g., 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM(Cl)), emerged as promising dehydro-condensation agents for amide synthesis, although suffering of limited stability and high costs. In the present work, a simple protocol for the synthesis of amides mediated by 2-chloro-4,6-dimethoxy-1,3,5-triazine (CDMT) and a tert-amine has been described and data are compared to DMTMM(Cl) and other CDMT-derived quaternary ammonium salts (DMT-Ams(X), X: Cl- or ClO4-). Different tert-amines (Ams) were tested for the synthesis of various DMT-Ams(Cl), but only DMTMM(Cl) could be isolated and employed for dehydro-condensation reactions, while all CDMT/tert-amine systems tested were efficient as dehydro-condensation agents. Interestingly, in best reaction conditions, CDMT and 1,4-dimethylpiperazine gave N-phenethyl benzamide in 93% yield in 15 min, with up to half the amount of tert-amine consumption. The efficiency of CDMT/tert-amine was further compared to more stable triazine quaternary ammonium salts having a perchlorate counter anion (DMT-Ams(ClO4)). Overall CDMT/tert-amine systems appear to be a viable and more economical alternative to most dehydro-condensation agents employed today.

Marine natural products

This review covers the literature published in 2019 for marine natural products (MNPs), with 719 citations (701 for the period January to December 2019) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1490 in 440 papers for 2019), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. Methods used to study marine fungi and their chemical diversity have also been discussed.

Antimicrobial and Antioxidant Polyketides from a Deep-Sea-Derived Fungus Aspergillus versicolor SH0105

Fifteen polyketides, including four new compounds, isoversiol F (1), decumbenone D (2), palitantin B (7), and 1,3-di-O-methyl-norsolorinic acid (8), along with 11 known compounds (3-6 and 9-15), were isolated from the deep-sea-derived fungus Aspergillus versicolor SH0105. Their structures and absolute configurations were determined by comprehensive spectroscopic data, including 1D and 2D NMR, HRESIMS, and ECD calculations, and it is the first time to determine the absolute configuration of known decumbenone A (6). All of these compounds were evaluated for their antimicrobial activities against four human pathogenic microbes and five fouling bacterial strains. The results indicated that 3,7-dihydroxy-1,9-dimethyldibenzofuran (14) displayed obvious inhibitory activity against Staphylococcus aureus (ATCC 27154) with the MIC value of 13.7 μM. In addition, the antioxidant assays of the isolated compounds revealed that aspermutarubrol/violaceol-I (15) exhibited significant 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity with the IC50 value of 34.1 μM, and displayed strong reduction of Fe3+ with the ferric reducing antioxidant power (FRAP) value of 9.0 mM under the concentration of 3.1 μg/mL, which were more potent than ascorbic acid.

Absolute Configurations and Chitinase Inhibitions of Quinazoline-Containing Diketopiperazines from the Marine-Derived Fungus Penicillium polonicum

Three new quinazoline-containing diketopiperazines, polonimides A–C (1–3), along with four analogues (4–7), were obtained from the marine-derived fungus Penicillium polonicum. Among them, 2 and 4, 3 and 5 were epimers, respectively, resulting the difficulty in the determination of their configurations. The configurations of 1–3 were determined by 1D nuclear overhauser effect (NOE), Marfey and electron circular dichroism (ECD) methods. Nuclear magnetic resonance (NMR) calculation with the combination of DP4plus probability method was used to distinguish the absolute configurations of C-3 in 3 and 5. All of 1–7 were tested for their chitinase inhibitory activity against OfHex1 and OfChi-h and cytotoxicity against A549, HGC-27 and UMUC-3 cell lines. Compounds 1–7 exhibited weak activity towards OfHex1 and strong activity towards OfChi-h at a concentration of 10.0 μM, with the inhibition rates of 0.7%–10.3% and 79.1%–95.4%, respectively. Interestingly, 1–7 showed low cytotoxicity against A549, HGC-27 and UMUC-3 cell lines, suggesting that good prospect of this cluster of metabolites for drug discovery.

Development of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methyl-morpholinium chloride cross-linked carboxymethyl cellulose films

First example of the use of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methyl-morpholinium chloride (DMTMM) as cross-linking agent for the development of carboxymethyl cellulose (CMC) films for food packaging is reported. Influence of different wt % of DMTMM and glycerol on the physical-mechanical properties of CMC films was investigated. The presence of DMTMM effectively improved moisture uptake, moisture content, water vapour permeability, water solubility of the films, oil resistance together with good biodegradability. Best compromise between high water resistance, vapour permeability and mechanical properties was accomplished with 5 wt % DMTMM and 50 wt % glycerol giving tensile strength and elongation at break of 52.25 ± 4.33 and 37.32 ± 2.04 respectively. DSC, TGA and SEM analysis further confirmed CMC cross-linking by DMTMM. All films prepared showed low opacity and high transparencies. Therefore, data reported show that DMTMM can efficiently cross-link CMC to produce films for food packaging.

Structure-Activity Relationships and Potent Cytotoxic Activities of Terphenyllin Derivatives from a Small Compound Library

A small library of 120 compounds was established with seventy new alkylated derivatives of the natural product terphenyllin, together with 45 previous reported derivatives and four natural p-terphenyl analogs. The 70 new derivatives were semi-synthesized and evaluated for cytotoxic activities against four cancer cell lines. Interestingly, 2',4''-diethoxyterphenyllin, 2',4,4''-triisopropoxyterphenyllin, and 2',4''-bis(cyclopentyloxy)terphenyllin showed potent activities with IC₅₀ values in a range from 0.13 to 5.51 μM, which were similar to those of the positive control, adriamycin. The preliminary structure-activity relationships indicated that the introduction of alkyl substituents including ethyl, allyl, propargyl, isopropyl, bromopropyl, isopentenyl, cyclopropylmethyl, and cyclopentylmethyl are important for improving the cytotoxicity.

Structures and Absolute Configurations of Diketopiperazine Alkaloids Chrysopiperazines A⁻C from the Gorgonian-Derived Penicillium chrysogenum Fungus

Three new diketopiperazine alkaloids, including two oxepine-containing diketopiperazines, chrysopiperazines A and B (1 and 2), and one quinazoline-containing diketopiperazine, chrysopiperazine C (5), together with three known analogues (3, 4, and 6), were isolated from the gorgonian-derived Penicillium chrysogenum fungus. The relative and absolute configurations of C-3 and C-15 in 1 and 2, C-3 and C-14 in 5 were established by NOE modified Marfey's analysis and electronic circular dichroism (ECD) calculations. Particularly, the absolute configurations of C-19 in 1 and 3, which was very challenging to be identified due to the flexible conformation in a short aliphatic chain, were successfully determined by the vibrational circular dichroism (VCD) method, supplying with a reliable and optional method to define the absolute configurations. Additionally, this is the first report on oxepine-containing diketopiperazines from the genus Penicillium.