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The development of peptide stapling techniques to stabilise α-helical secondary structure motifs of peptides led to the design of modulators of protein–protein interactions, which had been considered undruggable for a long time. We disclose a novel approach towards peptide stapling utilising macrocyclisation by late-stage Suzuki–Miyaura cross-coupling of bromotryptophan-containing peptides of the catenin-binding domain of axin. Optimisation of the linker length in order to find a compromise between both sufficient linker rigidity and flexibility resulted in a peptide with an increased α-helicity and enhanced binding affinity to its native binding partner β-catenin. An increased proteolytic stability against proteinase K has been demonstrated.

The phytochemical investigation of the methanol extract of the stem bark of Chrysophyllum lacourtianum led to the isolation and characterization of one new secondary metabolite, lacourtianal (1), together with eight known compounds. Compounds 2; 3; 5; 6; 7 and 9 were reported for the first time from Chrysophyllum genus. The structures of compounds 1–9 were elucidated on the basis of 1 D and 2 D NMR spectroscopic and mass spectrometric data as well as comparison with the literature. The antibacterial activity of the methanol extract, fractions and compounds 1–9 were evaluated against bacterial strains. The methanol extract exhibited moderate activity against Staphylococcus aureus NR4674 with MIC values of 500 µg/mL. The n-hexane fraction showed moderate activity against Staphylococcus aureus (ATCC 43300 and ATCC 25923) with MIC values of 125 µg/mL and ursolic acid (5) exhibited strong activity against Enterobacter aerogenes CPC and Escherichia coli ATCC 25322 with MIC values of 7.8 and 3.9 µg/mL respectively.

The antiplasmodium assay-guided investigation of the roots, stem bark, and leaves of Persea americana Mill. led to the isolation of a new fatty alcohol, perseatriol (1), along with six known compounds (2–7). Their structures were elucidated based on the analysis of their NMR and MS data. All crude extracts and fractions exhibited good antiplasmodial activity on Plasmoduim falciparum 3D7 with IC50 values ranging from 0.76 to 10.5 μg/mL; they also displayed cytotoxicity against HeLa cells with low selectivity indexes (SIs). A preliminary Plasmodium lactate dehydrogenase (pLDH) assay was also performed on the isolated compounds. 9,9′-Di-O-feruloyl-5,5′-dimethoxysecoisolariciresinol (4) turned out to be non-toxic and displayed the best activities on P. falciparum with an IC50 value of 0.05 μM, comparable to the reference drug chloroquine with an IC50 value of 0.03 μM. Furthermore, besides compound 4, this work reports the first isolation of lutein (2) and scopoletin (3) from P. americana. The crude extracts of roots, stem bark, and leaves of P. americana, their fractions and compounds completely suppressed the growth of P. falciparum. The observed activity supports the use of P. americana in folk medicine for the treatment of malaria.

Mild transition-metal catalysed cross-couplings enable direct functionalisation of biocatalytically halogenated tryptophans with alkyl iodides, representing a new alternative for late-stage derivatisations of halogenated aromatic amino acids. Moreover, this strategy enables a preparation of (homo)tryptophan regioisomers in a simple two-step synthesis using a Pd-catalysed Negishi cross coupling. This method provides access to non-canonical constitutional surrogates of tryptophan, ready for use in peptide synthesis. © 2021 Wiley-VCH GmbH.

A phytochemical study of the methanol extract of the fruit of Maesa lanceolata resulted in the isolation of a new alkenylbenzoquinone (1), alongside the known compounds (Z)-2,5-dihydroxy-6-methyl-3-(pentadec-10'-enyl)-1,4-benzoquinone (2), 2,5-dihydroxy-6-methyl-3-(nonadec-14'-enyl)-1,4-benzoquinone (3), 2,5-dihydroxy-6-methyl-3-(tridecyl)-1,4-benzoquinone (4), (2S,3S,4R,2'R,9E)-[2'-hydroxytetraeicosanoyl]-2-aminooctadec-9-ene-1,3,4-triol (5), monopalmitin (glyceryl palmitate) (6), lupeol (7), and 3-O-(β-D-glucopyranoside)-β-sitosterol (8). The structures of the compounds were established by the means of spectroscopic (1 D- and 2 D-NMR) and spectrometric techniques (MS). The isolated compounds were assessed for their antibacterial, cytotoxic, and antiradical activities. Compound 2 showed moderate activity against Staphylococcus warneri (DSMZ 20036), while the other compounds were inactive. The two quinones 1 and 2 were significantly cytotoxic, with IC50 values of 0.005 µM and 12.5 µM respectively, and were weakly active towards DPPH radical (IC50 >250 µg/mL).

Phytochemical investigation of the stem bark extract of Psychotria djumaensis led to the isolation of ten known pentacyclic triterpenoids among which one lupane-, three oleanane-, and six ursane-types. The structures of the isolated compounds were established by means of spectroscopic methods and by comparison with previously reported data. The isolated compounds were tested against five strains of bacteria, and the cytotoxicity against the human cervix carcinoma KB-3-1 cell was evaluated. The isolates exhibited weak antibacterial activity against the five strains. The cytotoxic activity exhibited by 3β,19α-dihydroxyurs-12-en-28-oic acid (5) (IC50 5.9 µM) was about three times more significant than that of the reference [(+) griseofulvin, IC50 17-21 µM].

The investigation of the methanolic extracts of the roots, stem bark and leaves of Manilkara obovata (Sabine & G. Don) J. H. Hemsl. (Sapotaceae), synonym Manilkara argentea Pierre ex Dubard, has led to the isolation and characterization of a new 4-phenylcoumarin derivative, in form of a racemic mixture of obovacoumaric acid (1a) and the previously reported callophyllic acid (1b) as well as a new taraxerane type triterpene named obovatol (2), alongside twenty-five known compounds. In addition, ethylcanophyllate (3a), obtained by esterification of canophyllic acid (3) is reported here for the first time. The structures of compounds were determined by comprehensive spectroscopic analyses of their 1D and 2D NMR, EI/ESI-MS and single crystal X-ray diffraction (SC-XRD) analysis for 1a and 1b, accompanied by comparison with reported records. In addition, the antibacterial activity of crude extracts, fractions and some of the isolated compounds including the hemi-synthesized ethylcanophyllate (3a) was determined against Salmonella typhi, Staphylococcus aureus ATCC4330, Enterobacter cloacae, Pseudomonas aeruginosa HM801, Streptococcus pneumoniae ATCC491619 and Escherichia coli ATCC25322 applying the broth microdilution method. While the methanolic stem bark extract showed good to significant activity against all bacterial test strains with MICs between 7.8 and 62.5 μg/mL, its fractions A and B were less active, indicating synergistic effects. This effect was also observed for the methanolic root extract, which gave a significant MIC against Staphylococcus aureus ATCC4330 with MIC < 3.9 μg/mL, but only MICs of 31.2 and 7.8 μg/mL for its fractions D and E. Likewise, though fractions F3 and F4 of the methanolic leaf extract displayed good MICs of 31.2 and 15.6 μg/mL, respectively, against Staphylococcus aureus ATCC4330, tested compounds were not stronger active. Interestingly, the hemi-synthesized ethylcanophyllate (3a) based on the completely antibacterial inactive canophyllic acid (3) displayed a good MIC of 15.6 μg/mL against Staphylococcus aureus ATCC4330, pointing here to a dominant role of the ester function in compound 3a in the structure-activity relationship.

Emerging drug-resistant bacteria creates an urgent need to search for antibiotics drugs with novel mechanisms of action. Endophytes have established a reputation as a source of structurally novel secondary metabolites with a wide range of biological activities. In the present study, we explore the antibacterial potential of endophytic fungi isolated from different tissues of Terminalia mantaly, Terminalia catappa, and Cananga odorata. The crude ethyl acetate extracts of 56 different endophytic fungi were screened against seven bacterial strains using the broth microdilution method. The antibacterial modes of action of the most active extracts (04) were evaluated using E. coli ATCC 25922 and H. influenzae ATCC 49247 strains. Both the DPPH and FRAP assays were used to investigate their antioxidant activity, and their cytotoxicity against the Vero cell line was evaluated using the MTT assay. Out of the 56 crude extracts tested, about 13% were considered very active, 66% partially active, and 21% nonactive against all tested bacterial strains with MIC values ranging from 0.32 μg/mL to 25 μg/mL. The four more potent extracts (MIC I C 50 ranging from 150.71 to 936.08 μg/mL. Three of the four potent extracts were noncytotoxic against the Vero cells line ( C C 50 > 100 μg/mL). Results from this investigation demonstrated that endophytes from Cameroonian medicinal plants might content potent antibacterial metabolites. The bioguided fractionation of these potent extracts is ongoing to isolate and characterise potential active ingredients.

A new alpha-pyrone, asperpyrone (1) and two known compounds, stigmasterol (2) and 7-hydroxy-3-(2,3-dihydroxybutyl)-1(3H)-Isobenzofuranone (3) were isolated from the solid rice culture of the endophytic fungus Aspergillus sp., an endophytic fungus isolated from the fresh inner tissue of the barks of Garicinia smeathmannii. Their structures were determined by extensive spectral analysis including 1D and 2D NMR, HRESIMS and single-crystal X-ray crystallographic analysis. Asperpyrone (1) was tested against an axenic culture of Entamoeba moshkovskii, but did not exhibit any significant amoebicidal activity.

Four hitherto unreported cycloartane-type triterpenes (1-4) with C-28/C-30 oxidized methyl groups together with two known compounds (5-6) have been obtained from the leaves and twigs of Caloncoba dusenii Gilg. The compounds were isolated through extraction and silica gel column chromatography. Their structures and relative stereochemistry were determined by extensive use of spectroscopic techniques including IR, 1D and 2D-NMR as well as mass spectrometry. This is the first report of C-28/C-30 oxidized positions in cycloartanes from nature.

A new flavone derivative named pachypodostyflavone (1), along with 8 known compounds (2–9) and a mixture of β-sitosterol and stigmasterol were isolated from the stem bark of Duguetia staudtii (Annonaceae), based on a bioassay-guided fractionation. Their structures were determined using high-resolution mass spectrometry and NMR spectroscopic data, as well as by comparison with the literature values of their analogs. Selected isolated compounds were evaluated for their in vitro antifilaricidal activities on Onchocerca ochengi microfilariae and adult worms. Inhibition of motility was evaluated spectroscopically on microfilaria and adult male worms. Viability was determined on adult female worms by the MTT/ Formazan assay. Auranofin at 10 µM and 2% DMSO were used as positive and negative controls, respectively. Compounds 1 and 7 showed potent anti-onchocerca activities with 100% activity at 250 µg/mL on both O. ochengi adult male and female worms, while compound 5 displayed 100% activity at 30 µg/mL.

A metal-free, atom-economy and simple work-up domino amination-Knoevenagel condensation approach to construct new coumarin analogous (4a-f and 8a-e) was described. Further, new formyl (5a,d-f) and nitro (9a,d-f) coumarin derivatives were synthesized via C-N coupling reaction of various cyclic secondary amines and 4-chloro-3-(formyl-/nitro)coumarins (1a,c), respectively. The confirmed compounds were screened for their in vitro anti-proliferative activity against KB-3-1, A549 and PC3 human cancer cell lines using resazurin cellular-based assay. Among them, coumarin derivatives 4e and 8e displayed the best anti-cervical cancer potency (KB-3-1) with IC50 values of 15.5 �� 3.54 and 21 �� 4.24 ��M, respectively. Also, 4e showed the most promising cytotoxicity toward A549 with IC50 value of 12.94 �� 1.51 ��M. As well, 9d presented a more significant impact of potency against PC3 with IC50 7.31 �� 0.48 ��M. Moreover, 8d manifested selectivity against PC3 (IC50 = 20.16 �� 0.07 ��M), while 8e was selective toward KB-3-1 cell line (IC50 = 21 �� 4.24 ��M). Matching with docking profile, the enzymatic assay divulged that 8e is a dual potent single-digit nanomolar inhibitor of VEGFR-2 and EGFR with IC50 values of 24.67 nM and 31.6 nM that were almost equipotent to sorafenib (31.08 nM) and erlotinib (26.79 nM), respectively.

In peptidotriazolamers every second peptide bond is replaced by a 1H-1,2,3-triazole. Such foldamers are expected to bridge the gap in molecular weight between small-molecule drugs and protein-based drugs. Amyloid beta (Abeta) aggregates play an important role in Alzheimer's disease. We studied the impact of amide bond replacements by 1,4-disubstituted 1H-1,2,3-triazoles on the inhibitory activity of the aggregation "hot spots" K16 LVFF20 and G39 VVIA42 in Abeta(1-42). We found that peptidotriazolamers act as modulators of the Abeta(1-42) oligomerization. Some peptidotriazolamers are able to interfere with the formation of toxic early Abeta oligomers, depending on the position of the triazoles, which is also supported by computational studies. Preliminary in vitro results demonstrate that a highly active peptidotriazolamer is also able to cross the blood-brain-barrier. © 2021 The Authors. ChemPlusChem published by Wiley-VCH GmbH.

The investigation of the CH2Cl2-MeOH (1:1) extract of Peperomia vulcanica which showed antileishmanial activity during preliminary screening led to the isolation of two previously unknown compounds named peperolignan (1) and peperotannin (2) along with 13 known compounds. Their structures were determined on the basis of their spectroscopic data. The isolated compounds were assessed in vitro for their antileishmanial and antiplasmodial activities against Leishmania donovani 1S (MHOM/SD/62/1S) promastigotes and the Plasmodium falciparum chloroquine-sensitive 3D7 strain (Pf3D7), respectively. They were also assessed for their cytotoxicity on Raw 264.7 macrophage cells. The mixture of 4-hydroxy-2-[(3,4-methylenedioxyphenyl)nonanoyl]cyclohexan-1,3-dione and 4-hydroxy-2-[(3,4-methylenedioxyphenyl) undecanoyl] cyclo-hexane-1,3-dione (10a and 10b) exhibited potent antiplasmodial activity (IC50 = 0.35 μg/mL) with selectivity index higher than 10-fold (SI = 63.4) and moderate leishmanicidal activity (IC50 = 12.17 μg/mL) with very low selectivity index (SI = 1.82). The obtained results could provide an extent of validation to the traditional uses of Peperomia vulcanica for the treatment of malaria in endemic areas.

The chemical study of Rumex abyssinicus Jacp (Polygonaceae) led to the isolation of a new ceramide named (R)-2'-hydroxy-N-[(2S,3S,4R,16E)-1,3,4-trihydroxyhexacos-16-en-2-yl]hexadecanamide (rumexamide) (1) together with sixteen known compounds: bis-(2-ethylhexyl) phthalate (2), chrysophanol (3), physcion (4), citreorosein (5), emodin (6), chrysophanein (7), physcionin (8), lupeol (9), 3β,28-dihydroxylup-20(29)-ene (10), 3β-dihydroxylup-20(29)-en-28-oic acid (11), oleanolic acid (12), ergosta-6,22-diene-3,5,8-triol (13), stigmastane-3,6-dione (14), a mixture of β-sitosterol (15) and stigmasterol (16), and stigmasterol 3-O-β-D-glucoside (17). Their structures were determined by interpretation of their spectroscopic 1D NMR (1H and 13C NMR), 2D NMR (COSY 1H-1H, HSQC and HMBC) data in conjunction with mass spectrometry (TOFESIMS and HR-TOFESIMS) and by comparison with those reported in the literature. Among all the known compounds, twelve (2, 5, 8-17) were firstly isolated from Rumex abyssinicus, seven (2, 10-14 and 17) from the genus Rumex and three (13, 14, 17) from family Polygonaceae. The in vitro antibacterial activities of extracts (MeOH, n-BuOH and EtOAc), as well as compounds 9, 11, 12, 15 + 16 and 17 against pathogenic bacteria (Staphylococcus aureus ATCC 43300, Shigella flexneri NR 518, Klebsiella pneumoniae ATCC 700603, Escherichia coli ATCC 25922), were performed using the broth microdilution method and the results show that, extracts were not active (MIC > 1000 μg/mL) while compounds were weakly or not active (MIC ≥ 500 μg/mL) against all bacteria strains. Furthermore, the chemophenetic relationships of the isolated compounds and their significances were discussed.

An array of l- and d-halotryptophans with different substituents at the indole moiety was synthesized employing either enzymatic halogenation by halogenases or incorporation of haloindoles using tryptophan synthase. Introduction of these Trp derivatives into RGD peptides as a benchmark system was performed to investigate their influence on bioactivity. Halotryptophan-containing RGD peptides display increased affinity toward integrin αvβ3 and enhanced selectivity over integrin α5β1. In addition, bromotryptophan was exploited as a platform for late-stage diversification by Suzuki–Miyaura cross-coupling (SMC), resulting in new-to-nature biaryl motifs. These peptides show enhanced affinity toward αvβ3, good affinity to αvβ8, and remarkable selectivity over α5β1 and αIIbβ3 while featuring fluorogenic properties. Their feasibility as a probe was demonstrated in vitro. Extensive molecular dynamics simulations were undertaken to elucidate NMR and high-performance liquid chromatography (HPLC) data for these late-stage diversified cyclic RGD peptides and to further characterize their conformational preferences.

The phytochemical investigation of Tarenna grandiflora led to the isolation of 18 known compounds of which were four flavones, three anthraquinones, one phenyl propanoic derivative, five triterpenoids, four steroids and a mixture of glucose. Luteolin (1) and soranjidiol (6) were allylated and/or prenylated to give four new semisynthesized derivatives which were fully characterized as 7,3′,4′-O-triallylluteolin (1a), luteolin-7,3′,4′-O-triprenyls (1b), luteolin-5,7,3′,4′-O-tetraprenyls (1c) and 6-O-allylsoranjidiol (6a). Their structures were established using spectroscopic analysis including 1D, 2D NMR and MS data. The cytotoxic, antioxidant and antimicrobial activities of extracts, fractions, isolated compounds and semi-synthesized derivatives were evaluated. The petroleum ether and EtOAc extracts exhibited good cytotoxic potency on KB-3-1 cell line with IC50 of >0.1 and 0.025 mg/mL respectively, while compounds 1b and 11 were the most active (IC50 > 0.0001 M). Compounds 1 and 3 showed the best antioxidant activities (45.5 and 55.8 µM); while compounds 9 and 12 showed the best antibacterial activities with MICs values ranges from 8.55 to 132 µM.

Mild reaction conditions are highly desirable for bio‐orthogonal side chain derivatizations of amino acids, peptides or proteins due to the sensitivity of these substrates. Transition metal catalysed cross‐couplings such as Suzuki–Miyaura reactions are highly versatile, but usually require unfavourable reaction conditions, in particular, when applied with aryl bromides. Ligand‐free solvent‐stabilised Pd‐nanoparticles represent an efficient and sustainable alternative to conventional phosphine‐based catalysts, because the cross‐coupling can be performed at considerably lower temperature. We report on the application of such a highly reactive heterogeneous catalyst for the Suzuki–Miyaura cross‐coupling of brominated tryptophan derivatives. The solvent‐stabilised Pd‐nanoparticles are even more efficient than the literature‐known ADHP‐Pd precatalyst. Interestingly, the latter also leads to the formation of quasi‐homogeneous Pd‐nanoparticles as the catalytic species. One advantage of our approach is the compatibility with aqueous and aerobic conditions at near‐ambient temperatures and short reaction times of only 2 h. The influence of different N α‐protecting groups, boronic acids as well as the impact of different amino acid side chains in bromotryptophan‐containing peptides has been studied. Notably, a surprising acceleration of the catalysis was observed when palladium‐coordinating side chains were present in proximal positions., Gentle conditions: Ligand‐free solvent‐stabilised Pd‐nanoparticles serve as a highly efficient catalyst at ambient temperature for a sustainable and biocompatible Suzuki–Miyaura cross‐coupling between aryl bromides and boronic acids under mild, aerobic and aqueous conditions.

The recently described flavin‐dependent halogenase BrvH is able to catalyse both the bromination and chlorination of indole, but shows significantly higher bromination activity. BrvH was annotated as a tryptophan halogenase, but does not accept tryptophan as a substrate. Its native substrate remains unknown. A predictive model with the data available for BrvH was analysed. A training set of compounds tested in vitro was docked into the active site of a complete protein model based on the X‐ray structure of BrvH. The atoms not resolved experimentally were modelled by using molecular mechanics force fields to obtain this protein model. Furthermore, docking poses for the substrates and known non‐substrates have been calculated. Parameters like distance, partial charge and hybridization state were analysed to derive rules for predicting activity. With this model for activity of the BrvH, a virtual screening suggested several structures for potential substrates. Some of the compounds preselected in this way were tested in vitro, and several could be verified as convertible substrates. Based on information on halogenated natural products, a new dataset was created to specifically search for natural products as substrates/products, and virtual screening in this database yielded further hits., To bind or not to bind? That is the question. The generation of a pharmacophore model adapted from a virtual screening methodology frequently employed in medicinal chemistry helped to suggest and identify new substrates for an orphan flavin‐dependent halogenase for which the native substrate is not yet known.

Phytochemical investigation of the fruits of Gambeya lacourtiana led to the isolation of four new compounds, lacourtianol (1), lacourtianoside I (2), lacourtianoside II (3) and lacourtianamide (4) together with six known compounds: 3-O-acetylbetulin (5), 3-O-acetylerythrodiol (6), β-amyrincaproate (7), lupeolhexanoate (8), erythrodiol 3-O-palmitate (9), and D-mannitol (10). The structures of 1-10 were elucidated on the basis of 1D and 2D NMR spectroscopic data, mass spectrometry and by comparison of spectroscopic data with those from the literature. Compounds 1-10 were evaluated for their antibacterial activity. Lacourtianoside II (3) exhibited moderate activity against Salmonella typhi CHU, Staphylococcus aureus (ATCC 43300 and ATCC 25923) and Enterobacter cloacae k2 with the same MIC value of 22.3 μM.

Cyclic RGD peptides are well‐known ligands of integrins. The integrins αVβ3 and α5β1 are involved in angiogenesis, and integrin αVβ3 is abundantly present on cancer cells, thus representing a therapeutic target. Hence, synthetic and biophysical studies continuously are being directed towards the understanding of ligand‐integrin interaction. In this context, the development of versatile synthetic strategies to obtain fluorescent building blocks that can add molecular diversity and modular spectral characteristics while not compromising binding affinity or selectivity is a relevant task. An on‐resin intramolecular Suzuki–Miyaura cross‐coupling (SMC) between l‐ or d‐7‐bromotryptophan (7BrTrp) and a phenothiazine (Ptz) boronic acid affords fluorescent cyclic RGD pseudopeptides, c(RGD(W/w)Ptz). Ring closure by SMC establishes a phenothiazine–indole moiety with axial chirality. An array of eight novel compounds has been synthesized, among them one fluorescent compound with good affinity to integrin αVβ3. The fluorescence properties of the analogues can be efficiently tuned depending on the substituents in Ptz moiety even for fluorescence emission in the visible (red) spectral range., Shiny RGD peptides: Cyclic peptides containing the tripeptide sequence Arg‐Gly‐Asp (RGD) have been equipped with a phenothiazine‐indole biaryl moiety by Suzuki–Miyaura cross‐coupling. Modulation of the spectroscopic properties by substituents at the phenothiazine provides blue and red fluorescent RGD derivatives that selectively bind to integrin αVβ3 in the best case with nanomolar affinity.

Halogenating enzymes are able to introduce halogen substituents under ambient conditions using non-hazardous reagents with intriguing selectivity, which is highly desired in green chemistry. Although C-H functionalization such as halogenation is a well-known transformation in synthetic chemistry, the selective incorporation of halogens using conventional chemical approaches often remains challenging. Therefore, enzyme-based strategies have been emerging as valuable alternatives in recent years. Inspired by manifold developments of enzymatic halogenation, this review focuses on advances of halogenating enzymes and their application with particular emphasis on FAD-dependent halogenases (FDHs). Catalytic strategies, application scope and engineering of FDHs are outlined pointing to the increasing utility of halogenases as promising biocatalysts. Current limitations as well as potential future developments of their synthetic utility are being discussed.

Two new norbergenin derivatives, 4-O-p-hydroxybenzoylnorbergenin (1) and 11-O-(E)-cinnamoylnorbergenin (2), were isolated from the leaves of Diospyros gilletii De Wild along with nine known compounds, including norbergenin (3), 4-O-galloylnorbergenin (4), betulin (5), betulinic acid (6), lupeol (7), ursolic acid (8), corosolic acid (9), beta-sitosterol (10) and quercitol (11). Their structures were elucidated from the analysis of their 1D and 2D H-1 and C-13 NMR spectral data in conjunction with mass spectrometry. Single-crystal X-ray diffraction technique unambiguously established the structure of compound (1). The antimicrobial properties of the eleven compounds isolated were investigated as well as the antioxidant activity of the norbergenin derivatives (1-4). The results obtained showed that none of those compounds displayed antimicrobial activity at 0.5 mu g/ml whereas norbergenin derivatives exhibited noteworthy antioxidant property with IC50 values ranging from 8.2 mu g/ml to 41.6 mu g/ml.

The crystal structure and unambiguous absolute configuration of meleagrin (1) isolated from fungus Emericella dentata Nq45 is reported herein to first time on the bases of single crystal X-ray diffraction. Together with 1, haenamindole (2), isorugulosuvine (3), secalonic acid D (4), ergosterol (5) and cerebroside A (6) were obtained and their structures were determined by ESI MS and NMR data analysis. Diverse biological activity of meleagrin (1) was investigated. Compound 1 pronounced potent cytotoxicity against the human cervix carcinoma cell line KB-3-1 and its multidrug resistant sub-clone KB-V1 of IC50 3.07 and 6.07 µM, respectively, in comparison with the reference (+) – griseofulvin (IC50 19, 19.5 µM). Based on the antibiofilm activity, compound 1 displayed as well potent activity against Staphylococcus aureus with an MIC of 0.25 mg/mL. Isolation of the producing fungus and taxonomical characterization is stated as well.

Pd‐mediated reactions have emerged as a powerful tool for the site‐selective and bioorthogonal late‐stage diversification of amino acids, peptides and related compounds. Indole moieties of tryptophan derivatives are susceptible to C2H‐activation, whereas halogenated aromatic amino acids such as halophenylalanines or halotryptophans provide a broad spectrum of different functionalisations. The compatibility of transition‐metal‐catalysed cross‐couplings with functional groups in peptides, other biologically active compounds and even proteins has been demonstrated. This Review primarily compiles the application of different cross‐coupling reactions to modify halotryptophans, halotryptophan containing peptides or halogenated, biologically active compounds derived from tryptophan. Modern approaches use regio‐ and stereoselective biocatalytic strategies to generate halotryptophans and derivatives on a preparative scale. The combination of bio‐ and chemocatalysis in cascade reactions is given by the biocompatibility and bioorthogonality of Pd‐mediated reactions., Pd‐mediated reactions have emerged as a powerful tool for the site‐selective and bioorthogonal late‐stage diversification of amino acids, peptides and related compounds. Halotryptophans are accessible by biocatalytic approaches opening the application of a variety of cross‐coupling reactions for late‐stage modification of halotryptophan containing biomolecules.

Misfolding and aggregation of amyloid β1–42 peptide (Aβ1–42) play a central role in the pathogenesis of Alzheimer's disease (AD). Targeting the highly cytotoxic oligomeric species formed during the early stages of the aggregation process represents a promising therapeutic strategy to reduce the toxicity associated with Aβ1–42. Currently, the thioflavin T (ThT) assay is the only established spectrofluorometric method to screen aggregation inhibitors. The success of the ThT assay is that it can detect Aβ1–42 aggregates with high β‐sheet content, such as protofibrils or fibrils, which appear in the late aggregation steps. Unfortunately, by using the ThT assay, the detection of inhibitors of early soluble oligomers that present a low β‐sheet character is challenging. Herein, a new, facile, and robust boron‐dipyrromethene (BODIPY) real‐time assay suitable for 96‐well plate format, which allows screening of compounds as selective inhibitors of the formation of Aβ1–42 oligomers, is reported. These inhibitors decrease the cellular toxicity of Aβ1–42, although they fail in the ThT assay. The findings have been confirmed and validated by structural analysis and cell viability assays under comparable experimental conditions. It is demonstrated that the BODIPY assay is a convenient method to screen and discover new candidate compounds that slow down or stop the pathological early oligomerization process and are active in the cellular assay. Therefore, it is a suitable complementary screening method of the current ThT assay., The sooner the better: Early amyloid beta (Aβ42) oligomers are known to be cytotoxic species in Alzheimer's disease. A real‐time boron‐dipyrromethene (BODIPY) fluorescence assay can be used to monitor the time course of the early stages of aggregation to provide valuable information on potential inhibitors of early Aβ42 oligomerization.

Azobenzenes are photoswitchable molecules capable of generating significant structural changes upon E-to-Z photoisomerization in peptides or small molecules, thereby controlling geometry and functionality. E-to-Z photoisomerization usually is achieved upon irradiation at 350 nm (π–π* transition), while the Z-to-E isomerization proceeds photochemically upon irradiation at >400 nm (n–π* transition) or thermally. Photoswitchable compounds have frequently been employed as modules, e.g., to control protein–DNA interactions. However, their use in conjunction with minor groove-binding imidazole/pyrrole (Im/Py) polyamides is yet unprecedented. Dervan-type Im/Py polyamides were equipped with an azobenzene unit, i.e., 3-(3-(aminomethyl)phenyl)azophenylacetic acid, as the linker between two Im/Py polyamide strands. Only the (Z)-azobenzene-containing polyamides bound to the minor groove of double-stranded DNA hairpins. Photoisomerization was exemplarily evaluated by 1H NMR experiments, while minor groove binding of the (Z)-azobenzene derivatives was proven by CD titration experiments. The resulting induced circular dichroism (ICD) bands of the bound ligands, together with the photometric determination of the dsDNA melting temperature, revealed a significant stabilization of the DNA upon association with the ligand. The (Z)-azobenzene acted as a building block inducing a reverse turn, which favored hydrogen bonds between the pyrrole/imidazole amide and the DNA bases. In contrast, the E-configured polyamides did not induce any ICD characteristic for minor groove binding. The incorporation of the photoswitchable azobenzene unit is a promising strategy to obtain photoswitchable Im/Py hairpin polyamides capable of interacting with the dsDNA minor groove only in the Z-configuration.

Two furanocoumarin derivatives, 3-methoxypsoralen (1) and 3,5-dimethoxypsoralen (2), along with nine known compounds, friedelinol (3), 3-oxo-11β-hydroxyoleanan-12-ene (4), lupeol (5), taraxer-3-one (6), a mixture of β-sitosterone (7a) and stigmast-4,22-dien-3-one (7b), ergosterol (8), 9,19-cyclolanost-3-one-24,25-diol (9), oleanan-12-ene-3,11-dione (10), and β-sitosterol 3-O-β-D-glucopyranoside (11) were isolated from the twigs of Ficus chlamydocarpa. Their structures were established by NMR spectroscopic analyses and HRESIMS. The structure of 1 was further confirmed from its single crystal X-ray diffraction. The crude extract, fractions and some isolated compounds were assessed for their preliminary antibacterial activity and cytotoxicity. One of the fractions (FB-B3) exhibited inhibition against the bacterial strain Pseudomonas agarici and induced a remarkable cytotoxic activity toward the human cervix carcinoma cell line KB-3-1 (IC50 0.166 mg/mL), and compounds 1, 6, and 7 showed moderate antibacterial activity against Bacillus subtilis and Micrococcus luteus.

Halogenases are valuable biocatalysts for selective C-H activation, but despite recent efforts to broaden their application scope by means of protein engineering, improvement of thermostability and catalytic efficiency is still desired. A directed evolution campaign aimed at generating a thermostable flavin-dependent tryptophan 6-halogenase with reasonable activity suitable for chemoenzymatic purposes. These characteristics were tackled by combining successive rounds of epPCR along with semi-rational mutagenesis leading to a triple mutant (Thal-GLV) with substantially increased thermostability (T-M=23.5 K) and higher activity at 25 degrees C than the wild type enzyme. Moreover, an active-site mutation has a striking impact on thermostability but also on enantioselectivity. Our data contribute to a detailed understanding of biohalogenation and provide a profound basis for future engineering strategies to facilitate chemoenzymatic application of these attractive biocatalysts.

Endophytes are prolific producers of privileged secondary metabolites with diverse therapeutic potential, although their anticancer and antimicrobial potential still have a room for further investigation. Herein, seven known secondary metabolites namely, arugosin C (1), ergosterol (2), iso-emericellin (3), sterigmatocystin (4), dihydrosterigmatocystin (5), versicolorin B (6), and diorcinol (7) were isolated from the rice culture of Aspergillus sp. retrieved from Tecoma stans (L.) Juss. ex Kunth leaves. Their anticancer and antimicrobial activities were evaluated in MTT and agar well diffusion assays, respectively. The cytotoxicity results showed that metabolite 3 displayed the best viability inhibition on the MCF-7 breast cancer cells with IC50 = 225.21 µM, while 5 on the HepG2 hepatocellular carcinoma cells with IC50 = 161.81 µM. 5 demonstrated a 60% apoptotic mode of cell death which is virtually correlated to its high docking affinity to Hsp90 ATP binding cleft (binding score −8.4 Kcal/mol). On the other side, metabolites 4 and 5 displayed promising antimicrobial activity especially on Pseudomonas aeruginosa with MIC = 125 μg/ml. The observed effect may be likely related to their excellent in silico inhibition of the bacterial DNA-gyrase kinase domain (binding score −10.28 Kcal/mol). To the best of our knowledge, this study is the first to report the promising cytotoxic and antibacterial activities of metabolites 3, 4, and 5 which needs further investigation and renovation to therapeutic leads.

Multiple, site-specific protein conjugation is increasingly attractive for the generation of antibody-drug conjugates (ADCs). As it is important to control the number and position of cargoes in an ADC, position-selective generation of reactive sites in the protein of interest is required. Formylglycine (FGly) residues are generated by enzymatic conversion of cysteine residues embedded in a certain amino acid sequence motif with a formylglycine-generating enzyme (FGE). The addition of copper ions increases FGE activity leading to the conversion of cysteines within less readily accepted sequences. With this tuned enzyme activity, it is possible to address two different recognition sequences using two aerobic formylglycine-generating enzymes. We demonstrate an improved and facile strategy for the functionalization of a DARPin (designed ankyrin repeat protein) and the single-chain antibody scFv425-Fc, both directed against the epidermal growth factor receptor (EGFR). The single-chain antibody was conjugated with monomethyl auristatin E (MMAE) and carboxyfluorescein (CF) and successfully tested for receptor binding, internalization, and cytotoxicity in cell culture, respectively.

Background Endodesmia calophylloides and Hymenostegia afzelii belong to the Guttiferae and Caesalpiniaceae plant families with known uses in African ethno-medicine to treat malaria and several other diseases. This study aimed at identifying antiplasmodial natural products from selected crude extracts from H. afzelii and E. calophylloides and to assess their cytotoxicity. Methods The extracts from H. afzelii and E. calophylloides were subjected to bioassay-guided fractionation to identify antiplasmodial compounds. The hydroethanol and methanol stem bark crude extracts, fractions and isolated compounds were assessed for antiplasmodial activity against the chloroquine-sensitive 3D7 and multi-drug resistant Dd2 strains of Plasmodium falciparum using the SYBR green I fluorescence-based microdilution assay. Cytotoxicity of active extracts, fractions and compounds was determined on African green monkey normal kidney Vero and murine macrophage Raw 264.7 cell lines using the Resazurin-based viability assay. Results The hydroethanolic extract of H. afzelii stem bark (HasbHE) and the methanolic extract of E. calophylloides stem bark (EcsbM) exhibited the highest potency against both Pf3D7 (EC50 values of 3.32 ± 0.15 μg/mL and 7.40 ± 0.19 μg/mL, respectively) and PfDd2 (EC50 of 3.08 ± 0.21 μg/mL and 7.48 ± 0.07 μg/mL, respectively) strains. Both extracts showed high selectivity toward Plasmodium parasites (SI > 13). The biological activity-guided fractionation led to the identification of five compounds (Compounds 1–5) from HasbHE and one compound (Compound 6) from EcsbM. Of these, Compound 1 corresponding to apigenin (EC50Pf3D7, of 19.01 ± 0.72 μM and EC50PfDd2 of 16.39 ± 0.52 μM), and Compound 6 corresponding to 3,3′-O-dimethylellagic acid (EC50Pf3D7 of 4.27 ± 0.05 μM and EC50PfDd2 of 1.36 ± 0.47 μM) displayed the highest antiplasmodial activities. Interestingly, both compounds exhibited negligible cytotoxicity against both Vero and Raw 264.7 cell lines with selectivity indices greater than 9. Conclusions This study led to the identification of two potent antiplasmodial natural compounds, 3,3′-O-dimethylellagic acid and apigenin that could serve as starting points for further antimalarial drug discovery.

Phytochemical investigation of the stem bark extract of Trichilia emetica led to the isolation of two new naturally occurring compounds including a prieurianin-class limonoid named trichirokin (1) and the steroid ergosta-5,24(28)-diene-3S, 16S, 20S-triol (4), along with nine known compounds characterized as rohituka-3 (3), rohituka-9 (2), scopoletin, benzoic acid, protocatechuic acid, lignoceric acid, beta-sitosterol, stigmasterol and beta-sitosterol-3-O-beta-D-glucopyranoside. The crystal structures of rohituka-3 (3) and ergosta-5,24(28)-diene-3S, 16S, 20S-triol (4) are reported here for the first time. The structures of the compounds were elucidated by extensive spectroscopic and spectrometric data interpretation. The stereochemistry of compound 1 was established on the basis of its NOESY spectrum and the comparison of its optical rotation value with that of its congener 2. None of the reported compounds displayed antibacterial or cytotoxic activity.

The first calcium complex from nature, Coumamarin (1), 7-hydroxy-3-methoxy-2-oxo-2H-chromene-6-carboxylate Ca(II) complex, was isolated from Aspergillus sydowii ASTI, together with diorcinol (2), violaceol I (3), hydroxysydonic acid (4), cyclo (Trp-Phe), kojic acid, ergosterol, and uracil. The producing strain was isolated from marine water sample collected from Tiran Island, Red Sea, Egypt. Structure 1 was assigned by intensive 1D, 2D NMR, HR-ESIMS, and X-ray crystallography as well. Coumamarin is potentially active against certain tested bacteria and yeasts, while showing no cytotoxic activity against human cervix carcinoma cell line (KB-3-1). Taxonomically, the fungus was identified by phylogenetic analysis of its 18S rRNA gene sequence.

A rotameric tryptamide alkaloid (1a-1b) was isolated from the methanolic extract of the roots of Vepris lecomteana together with the known compounds anhydroevoxine (2), lecomtequinoline C (3), evoxine (4), N-methylflindersine (5), evoxanthine (6), hesperidin, lupeol, beta-sitosterol and stigmasterol. The previously not reported 7-(3-anilino-2-hydroxyprenyloxy)-8-methoxydictamine (2a) was obtained by opening the epoxide of anhydroevoxine (2). The structures of above compounds were determined by comprehensive spectroscopic analyses of 1D and 2D NMR, EI-/ESI-MS, X-ray crystallography and comparison with the reported data. At room temperature, H-1 and C-13 NMR spectra show two rotamers (1a and 1b) with integrated intensities of 2/3, whereas at around 60 degrees C, only the 1b conformer was observed. Furthermore, the crystal structure of 1 was determined by the direct method of single crystal X-ray diffraction. The suggested biosynthesis for the formation of the new rotameric tryptamide alkaloid 1 is presented. Some of the isolated compounds (1, 2 and 2a) were tested in vitro against bacteria, resulting in weak for (1 and 2) to moderate activity for (2a) against Micrococcus Mulls and Escherichia coli with MIC values of 15.3 and 15.3 mu g/mL, respectively.

Flavin-dependent halogenases selectively introduce halogen substituents into (hetero-)aromatic substrates and require only molecular oxygen and halide salts for this regioselective oxidative CH-functionalization. Genomic analysis of Xanthomonas campestris pv. campestris B100 identified three novel putative members of this enzyme class. They were shown to introduce halogen substituents into, e. g., substituted indoles, while preferring bromide over chloride.

l-Amino acid oxidases (LAAOs) are flavoproteins, which use oxygen to deaminate l-amino acids and produce the corresponding α-keto acids, ammonia, and hydrogen peroxide. Here we describe the heterologous expression of LAAO4 from the fungus Hebeloma cylindrosporum without signal sequence as fusion protein with a 6His tag in Escherichia coli and its purification. 6His-hcLAAO4 could be activated by exposure to acidic pH, the detergent sodium dodecyl sulfate, or freezing. The enzyme converted 14 proteinogenic l-amino acids with l-glutamine, l-leucine, l-methionine, l-phenylalanine, l-tyrosine, and l-lysine being the best substrates. Methyl esters of these l-amino acids were also accepted. Even ethyl esters were converted but with lower activity. Km values were below 1 mM and vmax values between 19 and 39 U mg−1 for the best substrates with the acid-activated enzyme. The information for an N-terminal aldehyde tag was added to the coding sequence. Co-expressed formylglycine-generating enzyme was used to convert a cysteine residue in the aldehyde tag to a Cα-formylglycine residue. The aldehyde tag did not change the properties of the enzyme. Purified Ald-6His-hcLAAO4 was covalently bound to a hexylamine resin via the Cα-formylglycine residue. The immobilized enzyme could be reused repeatedly to generate phenylpyruvate from l-phenylalanine with a total turnover number of 17,600 and was stable for over 40 days at 25 °C.

Tryptophan (Trp) derivatives constitute important building blocks found in many natural products, peptides, and drugs. Accordingly, there is a high demand for suitable biocatalytic pathways providing selective derivatization of Trp like C-H functionalization or C-alpha-oxidation. The specific l-amino acid oxidase RebO from the actinomycete L. aerocolonigenes was harnessed for chemoenzymatic oxidation of substituted Trp derivatives. An array of potential substrates was tested, and several Trp derivatives are being accepted with reasonable turnover. The highest selectivity was observed for 7-halotryptophan being converted about 35-fold faster than nonsubstituted Trp. This selectivity is also useful for establishing a colorimetric halogenase high-throughput assay. RebO was also employed in dynamic stereoinversion in the presence of an ammonia-borane complex to provide access to non-native D-configured Trp analogues. Optimized reaction conditions yielded similar to 70% D-amino acid with >98% ee for halotryptophans on an analytical scale. Dynamic stereoinversion preceded by enzymatic halogenation in a sequential one-pot reaction cascade provided D-configured 5- or 7-bromotryptophan with improved conversion of approximately 90%, >92% ee, and good isolated yields.

Background Plants represent an intricate and innovative source for the discovery of novel therapeutic remedies for the management of infectious diseases. The current study aimed at discovering new inhibitors of Leishmania spp., using anti-leishmanial activity-guided investigation approach of extracts from Diospyros gracilescens Gürke (1911) (Ebenaceae), targeting the extracellular (promastigotes) and intracellular (amastigotes) forms of Leishmania donovani. Methods The plant extracts were prepared by maceration using H20: EtOH (30:70, v/v) and further fractionated using a bio-guided approach. Different concentrations of D. gracilescens extracts, fractions and isolated compounds were tested in triplicate against L. donovani promastigotes and amastigotes in vitro. The antileishmanial potency and cytotoxicity on RAW 264.7 cells were determined using the resazurin colorimetric assay. The time kill kinetic profile of the most active sample was also investigated. The structures of all compounds were elucidated on the basis of extensive spectroscopic analyses, including 1D and 2D NMR, and HR-ESI-MS and by comparison of their data with those reported in the literature. Results The hydroethanolic crude extract of D. gracilescens trunk showed the most potent antileishmanial activity (IC50 = 5.84 μg/mL). Further fractionation of this extract led to four (4) fractions of which, the hexane fraction showed the most potent activity (IC50 = 0.79 μg/mL), and seven (07) compounds that exhibited moderate potency (IC50 = 13.69–241.71 μM) against L. donovani. Compound 1-deoxyinositol (7) inhibited the promastigote and amastigote forms of L. donovani with IC50 values of 241.71 μM and 120 μM respectively and also showed the highest selectivity against L. donovani promastigotes (SI > 5.04). To the best of our knowledge, the antileishmanial activity of this compound is being reported here for the first time. The promising hexane fraction showed significant inhibition of parasites growth at different concentrations, but with no evidence of cidal effect over an exposure period of 120 h. Conclusions The results obtained indicated that the hydroethanolic extract from the D. gracilescens trunk and the derived hexane fraction have very potent inhibitory effect on cultivated promastigotes and amastigotes of L. donovani parasite. The isolated compounds showed a lesser extent of potency and selectivity. However, further structure-activity-relationship studies of 1-deoxyinositol could lead to more potent and selective hit derivatives of interest for detailed drug discovery program against visceral leishmaniasis.

Phytochemical investigation of the stem barks of Ficus exasperata Vahl. (Moraceae) led to the isolation of two new cinnamic acid derivatives stereoisomers, named ficusanolide A (1) and ficusanolide B (2) along with twelve known compounds: ficusanol (3), umbelliferone-6-carboxylic acid (4), oxypeucedanin hydrate (5), marmesin (6), decursinol (7), beta-amyrin acetate (8), lupeol (9), betulinic acid (10), ursolic acid (11), a mixture of stigmasterol (12) and beta-sitosterol (13), sitosteryl-3-O-beta-D-glucopyranoside (14); and one hemisynthetic derivative : per acetylated betulinic acid (15). Their structures were established by the means of their physical data (melting point, rotatory power), their spectroscopic data, particularly IR, NMR (1H, 13C, DEPT, COSY, HSQC and HMBC) data, and HR-ESIMS data. Crude extract, compounds 1, 2, 3, 5, 6, 7, 9, 10, 11, as well as the semisynthetic derivative 15 were evaluated for their cytotoxic activity on the human cervix carcinoma cell line KB-3-1 and the human colon cancer cell line HT-29. Ursolic acid 11 showed a moderate activity on both cancer cells tested with IC50s of 50.9 mu M and 34.4 mu M respectively.

From the crude extract of the plant-associated fungus Xylaria sp. collected in Cameroon, a new 2 H-chromene derivative, hexacycloxylariolone (1), and a new polyalcohol, xylatriol (2), were isolated, in addition to 3 known compounds, 2,3-furandiol (3), 1,8-dimethoxynaphthalene (4), and 1-palmitoyl-rac-glycerol (5). Their chemical structures were established on the basis of the interpretation of spectroscopic data. Hexacycloxylariolone (1), 1,8-dimethoxynaphthalene (4), and 1-palmitoyl-rac-glycerol (5) showed antiproliferative activity by inhibiting the growth of Raw 264.7 and THP-1 cancer cell lines.

A phytochemical investigation of the roots of Celtis adolphi-friderici Engl. led to the isolation of a previously undescribed cerebroside named, eloundemnoside (1), alongside with seventeen known compounds (2–18). Their chemical structures were elucidated based on the analysis of their NMR and MS data. All the compounds were isolated from this specie for the first time, while eight known compounds (4–5, 12–13, 15–18) are obtained from the genus Celtis for the first time. The isolates were screened for their antioxidant, lipoxygenase, urease, and butyrylcholinesterase enzyme inhibitory activities. Compounds 4, 7 and 12 showed good antioxidant activities with IC50 values of 22.2, 29.3, and 13.2 μM, respectively. In addition, azelaic acid (12) showed the best lipoxygenase inhibition (IC50 value of 16.3 μM), while friedelin (2) exhibited the highest inhibition of urease with an IC50 value of 15.3 μM. However, all the compounds tested had moderate butyrylcholinesterase inhibitory properties. The chemophenetic relationship of the isolates and their significance were discussed.