Biomimetic synthesis, antimicrobial, antileishmanial and antimalarial activities of euglobals and their analogues

Formyl phloroglucinol meroterpenoids from the leaves of Eucalyptus globulus subsp. maidenii and their ATP-citrate lyase inhibitory activities

Three new formyl phloroglucinol meroterpenoids, eumaidials A-C (1-3), were isolated from the leaves of Eucalyptus globulus subsp. maidenii, along with ten known analogues (4-13). Their chemical structures were determined by various spectral data and electronic circular dichroism calculations. Eumaidial A (1) is the first β-caryophyllene-based formyl phloroglucinol meroterpenoids from the genus Eucalyptus. Compounds 1-4 and 10 exhibited ATP-citrate lyase inhibitory activities, and compounds 2 and 3 suppressed the hepatocyte lipogenesis.

Biomimetic Synthesis and Chemical Proteomics Reveal the Mechanism of Action and Functional Targets of Phloroglucinol Meroterpenoids

Natural products perennially serve as prolific sources of drug leads and chemical probes, fueling the development of numerous therapeutics. Despite their scarcity, natural products that modulate protein function through covalent interactions with lysine residues hold immense potential to unlock new therapeutic interventions and advance our understanding of the biological processes governed by these modifications. Phloroglucinol meroterpenoids constitute one of the most expansive classes of natural products, displaying a plethora of biological activities. However, their mechanism of action and cellular targets have, until now, remained elusive. In this study, we detail the concise biomimetic synthesis, computational mechanistic insights, physicochemical attributes, kinetic parameters, molecular mechanism of action, and functional cellular targets of several phloroglucinol meroterpenoids. We harness synthetic clickable analogues of natural products to probe their disparate proteome-wide reactivity and subcellular localization through in-gel fluorescence scanning and cell imaging. By implementing sample multiplexing and a redesigned lysine-targeting probe, we streamline a quantitative activity-based protein profiling, enabling the direct mapping of global reactivity and ligandability of proteinaceous lysines in human cells. Leveraging this framework, we identify numerous lysine-meroterpenoid interactions in breast cancer cells at tractable protein sites across diverse structural and functional classes, including those historically deemed undruggable. We validate that phloroglucinol meroterpenoids perturb biochemical functions through stereoselective and site-specific modification of lysines in proteins vital for breast cancer metabolism, including lipid signaling, mitochondrial respiration, and glycolysis. These findings underscore the broad potential of phloroglucinol meroterpenoids for targeting functional lysines in the human proteome.

Synthesis of Coumarin-Conjugated Oligonucleotides via Knoevenagel Condensation to Prepare an Oligonucleotide Library

DNA-encoded libraries (DELs) are attracting attention as a screening tool in the early stages of drug discovery. In the development of DELs, drug candidate compounds are chemically synthesized on barcode DNA. Therefore, it is important to perform the synthesis under mild conditions so as to not damage the DNA. On the other hand, coumarins are gaining increasing research focus not only because they possess excellent fluorescence properties, but also because many medicines contain a coumarin skeleton. Among the various reactions developed for the synthesis of coumarins thus far, Knoevenagel condensation followed by intramolecular cyclization under mild conditions can yield coumarins. In this study, we developed a new synthetic method for preparing a coumarin-conjugated oligonucleotide library via Knoevenagel condensation. The results showed that coumarins substituted at the 5-, 6-, 7-, or 8-positions could be constructed on DNA to afford a total of 26 coumarin-conjugated DNAs. Moreover, this method was compatible with enzymatic ligation, demonstrating its utility in DEL synthesis. The developed strategy for the construction of coumarin scaffolds based on Knoevenagel condensation may contribute to the use of DELs in drug discovery and medicinal chemistry.

Camaldulensals A-C, the First Meroterpenoids Possessing Two Spatially Separated Formyl Phloroglucinols Conjugated to a Terpene Core from the Leaves of Eucalyptus camaldulensis Dehnh

Three new bis-formyl phloroglucinol-meroterpenoids (1-3), three new euglobal type formyl phloroglucinol-meroterpenoids (4-6), and one new dimeric formyl phloroglucinol (7) were isolated from the leaves of Eucalyptus camaldulensis. Camaldulensal A (1) is the first bis-isovaleryl-formyl-phloroglucinol-sesquiterpenoid. It features a novel 6/6/10/3/6/6 fused ring system and contains six stereogenic centers. Camaldulensals B (2) and C (3) are the first bis-isovaleryl-formyl-phloroglucinols, each conjugated to a monoterpene. Formyl phloroglucinol compounds (FPCs) containing two spatially separated formyl phloroglucinols conjugated to a terpene core such as 1-3 have not been reported previously. The structures of these compounds were elucidated by spectroscopic methods and computational analysis. Camaldulensals B (2) and C (3) exhibited significant antibacterial activity against methicillin-susceptible and methicillin-resistant Staphylococcus aureus. Structure activity relationships are discussed in relation to previously reported antibacterial activities of other molecules from the FPC structure class.

Acylphloroglucinol-monoterpene meroterpenoids from Eucalyptus tereticornis and their inhibitory activity against ATP citrate lyase

Five undescribed enantiomeric pairs of acylphloroglucinol-monoterpene meroterpenoids ((+)-/(-)-eucateretins A-E) resolved by chiral-phase HPLC were obtained from the leaves of Eucalyptus tereticornis Smith, along with nine known analogues. Their structures were elucidated by spectroscopic methods and ECD calculations. This is the first report of meroterpenoid enantiomers from this plant. Some of the isolates, (-)-eucateretin A, (+)-/(-)-eucateretins E, 7'α-eucalrobusone X, eucalrobusone X, and robustadial B, exhibited inhibitory effects on ATP citrate lyase, and 7'α-eucalrobusone X significantly suppressed the hepatocyte lipogenesis.

Derivatives of Natural Product Agrimophol as Disruptors of Intrabacterial pH Homeostasis in Mycobacterium tuberculosis

This article reports the rational medicinal chemistry of a natural product, agrimophol (1), as a new disruptor of intrabacterial pH (pH_IB) homeostasis in Mycobacterium tuberculosis (Mtb). Through the systematic investigation of the structure-activity relationship of 1, scaffold-hopping of the diphenylmethane scaffold, pharmacophore displacement strategies, and studies of the structure-metabolism relationship, a new derivative 5a was achieved. Compound 5a showed 100-fold increased potency in the ability to reduce pH_IB to pH 6.0 and similarly improved mycobactericidal activity compared with 1 against both Mycobacterium bovis-BCG and Mtb. Compound 5a possessed improved metabolic stability in human liver microsomes and hepatocytes, lower cytotoxicity, higher selectivity index, and similar pK_a value to natural 1. This study introduces a novel scaffold to an old drug, resulting in improved mycobactericidal activity through decreasing pH_IB, and may contribute to the critical search for new agents to overcome drug resistance and persistence in the treatment of tuberculosis.

Study and modeling of the distribution process of some phenolic compounds between the solid and liquid phases

The article presents the results related to the study of distribution of biologically active substances from the plant raw material between solid and liquid phases. The aim of this study is to develop theoretical bases of the extraction process in the equilibrium state by the example of study and modeling of the distribution process of biologically active substances from Eucalyptus viminalis leaves. In these studies, we used ground plant raw material of E. viminalis leaves with particle fraction of 0.1-0.5 mm; and ethanol with concentration 80% ±1% v/v was used as an extractant. Qualitative and quantitative analyses were carried out by reversed phase high-performance liquid chromatography with rutin, chlorogenic acid, and euglobal standards equivalent to spissum extract of chlorophyllipt of the State Pharmacopoeia of Ukraine. A hypothesis has been suggested that Henry's adsorption law and the law of conservation of matter play a fundamental role in this process. The experimental data are described well by the suggested equation with high value of determination coefficient R ² =0.99. At the same time, F-test and the significance of coefficients in equations satisfy the statistic condition, which means that the current hypothesis about the adsorption mechanism of distribution of biologically active substances in the extraction system is not refuted. The results of these studies demonstrate good agreement of experimental data and theoretical model based on Henry's adsorption law and mass balance. The numerical values of constants in the model suggested have been calculated.

Biomimetic total syntheses of chromane meroterpenoids, guadials B and C, guapsidial A and psiguajadial D

The first biomimetic total syntheses of chromane meroterpenoids, guadials B and C, guapsidial A and psiguajadial D have been completed. The key synthetic transformation involves an efficient and high yielding hetero-Diels-Alder reaction. The two structurally isomeric natural products, guadials B and C, were obtained from a common o-quinone methide in the separate reactions with α-pinene and β-pinene, respectively. The two regioisomeric natural products, guapsidial A and psiguajadial D, were achieved in a single chemical operation.

Quantification and Localization of Formylated Phloroglucinol Compounds (FPCs) in Eucalyptus Species

The Eucalyptus genus is a hyper-diverse group of long-lived trees from the Myrtaceae family, consisting of more than 700 species. Eucalyptus are widely distributed across their native Australian landscape and are the most widely planted hardwood forest trees in the world. The ecological and economic success of Eucalyptus trees is due, in part, to their ability to produce a plethora of specialized metabolites, which moderate abiotic and biotic interactions. Formylated phloroglucinol compounds (FPCs) are an important class of specialized metabolites in the Myrtaceae family, particularly abundant in Eucalyptus. FPCs are mono- to tetra-formylated phloroglucinol based derivatives, often with an attached terpene moiety. These compounds provide chemical defense against herbivory and display various bioactivities of pharmaceutical relevance. Despite their ecological and economic importance, and continued improvements into analytical techniques, FPCs have proved challenging to study. Here we present a simple and reliable method for FPCs extraction, identification and quantification by UHPLC-DAD-ESI-Q-TOF-MS/MS. The method was applied to leaf, flower bud, and flower samples of nine different eucalypt species, using a small amount of plant material. Authentic analytical standards were used to provide high resolution mass spectra and fragmentation patterns. A robust method provides opportunities for future investigations into the identification and quantification of FPCs in complex biological samples with high confidence. Furthermore, we present for the first time the tissue-based localization of FPCs in stem, leaf, and flower bud of Eucalyptus species measured by mass spectrometry imaging, providing important information for biosynthetic pathway discovery studies and for understanding the role of those compounds in planta.

Natural products as sources of new fungicides (IV): Synthesis and biological evaluation of isobutyrophenone analogs as potential inhibitors of class-II fructose-1,6-bisphosphate aldolase

Several recently identified antifungal compounds share the backbone structure of acetophenones. The aim of the present study was to develop new isobutyrophenone analogs as new antifungal agents. A series of new 2,4-dihydroxy-5-methyl isobutyrophenone derivatives were prepared and characterized by ¹H, ¹³C NMR and MS spectroscopic data. These products were evaluated for in vitro antifungal activities against seven plant fungal pathogens by the mycelial growth inhibitory rate assay. Compounds 3, 4a, 5a, 5b, 5e, 5f and 5g showed a broad-spectrum high antifungal activity. On the other hand, for the first time, these compounds were also assayed as potential inhibitors against Class II fructose-1,6-bisphosphate aldolase (Fba) from the rice blast fungus, Magnaporthe grisea. Compounds 5e and 5g were found to exhibit the inhibition constants (Ki) for 15.12 and 14.27 μM, respectively, as the strongest competitive inhibitors against Fba activity. The possible binding-modes of compounds 5e and 5g were further analyzed by molecular docking algorithms. The results strongly suggested that compound 5g could be a promising lead for the discovery of new fungicides via targeting Class II Fba.

Multicomponent Condensation Reactions via ortho-Quinone Methides

Iron(III) salts promote the condensation of aldehydes or acetals with electron-rich phenols to generate ortho-quinone methides that undergo Diels-Alder condensations with alkenes. The reaction sequence occurs in a single vessel to afford benzopyrans in up to 95% yield. The reaction was discovered while investigating a two-component strategy using 2-(hydroxy(phenyl)methyl)phenols to access the desired ortho-quinone methide in a Diels-Alder condensation. The two-component condensation also afforded the corresponding benzopyran products in yields up to 97%. Taken together, the two- and three-component strategies using ortho-quinone methide intermediates provide efficient access to benzopyrans in good yields and selectivities.

Synthesis and Antimalarial Activity of Mallatojaponin C and Related Compounds

The phloroglucinol mallotojaponin C (1) from Mallotus oppositifolius, which was previously shown by us to have both antiplasmodial and cytocidal activities against the malaria parasite Plasmodium falciparum, was synthesized in three steps from 2',4',6'-trihydroxyacetophenone, and various derivatives were synthesized in an attempt to improve the bioactivity of this class of compounds. Two derivatives, the simple prenylated phloroglucinols 12 and 13, were found to have comparable antiplasmodial activities to that of mallotojaponin C.

Divergent Total Syntheses of Rhodomyrtosones A and B

Herein, we report total syntheses of the tetramethyldihydroxanthene natural product rhodomyrtosone B and the related bis-furan β-triketone natural product rhodomyrtosone A. Nickel-(II)-catalyzed 1,4-conjugate addition of an α-alkylidene-β-dicarbonyl substrate was developed to access the congener rhodomyrtosone B, and oxygenation of the same monoalkylidene derivative followed by cyclization was employed to obtain the bis-furan natural product rhodomyrtosone A.

The Mosaic of Rottlerin

The first total synthesis of rottlerin is described. The methodology allows the development of potential novel protein kinase C δ (PKCδ) analogues for better treatment of various diseases. Kamalachalcone A and dimeric rottlerin were synthesized in a very practical and economical way using FeCl3 as a catalyst.

Farnesol induces apoptosis of DU145 prostate cancer cells through the PI3K/Akt and MAPK pathways

The aim of this study was to investigate the effect of farnesol on the induction of apoptosis in DU145 prostate cancer cells. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay showed that cell proliferation decreased significantly in a dose- and time-dependent manner. 4',6-Diamidino-2-phenylindole staining showed that chromatin condensation in cells treated with 60 µM of farnesol was markedly higher than in the control groups. Farnesol increased the expression of p53, p-c-Jun N-terminal kinase, cleaved-caspase-3, Bax, and cleaved-caspase-9, but decreased the expression of p-phosphatidylinositol-3-kinase (PI3K), p-Akt, p-p38, Bcl-2, and p-extracellular signal-regulated protein kinase, in a dose-dependent manner. The apoptotic cell ratio increased in a dose-dependent manner. The tumor growth inhibitory effect of farnesol was investigated in a mouse model. Compared to the control group, tumor volume decreased significantly in the group administered 50 mg/kg farnesol. Apoptosis was frequently detected in this same group by terminal deoxynucleotidyl transferase dUTP nick-end labeling assay. The results indicated that farnesol induced apoptosis of DU145 prostate cancer cells through the PI3K/Akt and mitogen-activated protein kinase signaling pathways.

Five New Acylphloroglucinol Glycosides from the Leaves of Eucalyptus robusta

Five new acylphloroglucinol glycosides, robustasides A-E (1–5), together with a known one (6), were isolated from the leaves of Eucalyptus robusta. The structures were elucidated on the basis of extensive spectroscopic and spectrometric analysis and chemical evidence. The absolute configuration of 1 was further determined by quantum chemical CD calculation.

ortho-Quinone methide (o-QM): a highly reactive, ephemeral and versatile intermediate in organic synthesis

In this critical review, we provide a comprehensive view of the chemistry of ortho-quinone methides as versatile reactive intermediates in organic synthesis.

Two new euglobals from the leaves of Eucalyptus robusta

Two new euglobals, R1 (1) and R2 (2), together with eight known euglobals (3-10) were isolated from the leaves of Eucalyptus robusta. Their structures were established by means of spectroscopic analysis and single-crystal X-ray diffraction. Euglobal R1 (1) represents a new skeleton of formyl-isovaleryl phloroglucinol-coupled β-phellandrene.

Euglobal-IIIa, a novel acylphloroglucinol-sesquiterpene derivative from Eucalyptus robusta: absolute structure and cytotoxicity

Euglobal-IIIa (1), a novel acylphloroglucinol-sesquiterpene derivative, and a known analogue, have been isolated from leaves of Eucalyptus robusta. The structures was elucidated by extensive spectroscopic data and by comparison with data reported in literature, while the absolute configuration of 1 was determined by the X-ray diffraction analysis. Compound 1 exhibited comparable cytotoxicity with that of cisplatin against five human cancer cell lines HL-60, SMMC-7721, A-549, MCF-7, and SW480 with IC₅₀ values of 15.7, 15.5, 17.6, 14.3, and 21.8 µM, respectively.

Quantitative Analysis of Euglobals in Eucalyptus loxophleba Leaves by qNMR¶

A simple, rapid, accurate and selective 1H NMR spectroscopic method to detect and quantify euglobals in the leaves of Eucalyptus loxophleba ssp. lissophloia has been developed. The method allows for the estimation of total concentration of diformylphloroglucinol-monoterpene adducts, as well as the quantitation of sabinene- and α/β-phellandrene-adducts, separately. The method was validated for accuracy, precision and linearity using as reference standards 2-ethyl phenol and mixtures of jensenone, a monomeric formylated phloroglucinol, and 2-ethyl phenol.

Trends in malaria research in 11 Asian Pacific countries: an analysis of peer-reviewed publications over two decades

Background

Quantitative data are lacking on published malaria research. The purpose of the study is to characterize trends in malaria-related literature from 1990 to 2009 in 11 Asian-Pacific countries that are committed to malaria elimination as a national goal.

Methods

A systematic search was conducted for articles published from January 1990 to December 2009 in PubMed/MEDLINE using terms for malaria and 11 target countries (Bhutan, China, North Korea, Indonesia, Malaysia, Philippines, Solomon Islands, South Korea, Sri Lanka, Thailand and Vanuatu). The references were collated and categorized according to subject, Plasmodium species, and whether they contained original or derivative data.

Results

2,700 articles published between 1990 and 2009 related to malaria in the target countries. The annual output of malaria-related papers increased linearly whereas the overall biomedical output from these countries grew exponentially. The percentage of malaria-related publications was nearly 3% (111/3741) of all biomedical publications in 1992 and decreased to less than 1% (118/12171; p < 0.001) in 2009. Thailand had the highest absolute output of malaria-related papers (n = 1211), followed by China (n = 609) and Indonesia (n = 346). Solomon Islands and Vanuatu had lower absolute numbers of publications, but both countries had the highest number of publications per capita (1.3 and 2.5 papers/1,000 population). The largest percentage of papers concerned the epidemiology and control of malaria (53%) followed by studies of drugs and drug resistance (47%). There was an increase in the proportion of articles relating to epidemiology, entomology, biology, molecular biology, pathophysiology and diagnostics from the first to the second decade, whereas the percentage of papers on drugs, clinical aspects of malaria, immunology, and social sciences decreased.

Conclusions

The proportion of malaria-related publications out of the overall biomedical output from the 11 target Asian-Pacific countries is decreasing. The discovery and evaluation of new, safe and effective drugs and vaccines is paramount. In addition the elimination of malaria will require operational research to implement and scale up interventions.

Antibacterial sideroxylonals and loxophlebal A from Eucalyptus loxophleba foliage

Loxophlebal A, a new antibacterial formylated phloroglucinol was isolated from the mother liquor obtained after separation of sideroxylonals from the chloroform-methanol extract of leaves of Eucalyptus loxophleba ssp lissophloia. The structure of loxophlebal A was determined to be 3-desformyl sideroxylonal A by spectroscopic methods including 1D- and 2D-NMR. The stereochemistry of loxophlebal A was determined by chemical correlation with sideroxylonal A. This article also reports an efficient, simple and economic method for large scale isolation of sideroxylonals in a purity of >90% from the leaves of Eucalyptus loxophleba ssp lissophloia.

Sequential five-component synthesis of spiropyrrolidinochromanones

Herein we report a novel, diastereoselective, one-pot, two-step, sequential synthesis of highly functionalized natural product-like spiropyrrolidinochromanones. The process consists of an Ugi four-component condensation of 3-formylchromones with amines, isocyanides, and glyoxylic acids followed by a nucleophilic conjugate addition and intramolecular cyclization. The experimental simplicity and tolerance to a wide variety of substituents makes this method suitable for combinatorial synthesis.

Discovery of diacylphloroglucinols as a new class of GPR40 (FFAR1) agonists

In this letter, we report discovery of diacylphloroglucinol compounds as a new class of GPR40 (FFAR1) agonists. Several diacylphloroglucinols with varying length of acyl functionality and substitution on aromatic hydroxyls were synthesized and evaluated for GPR40 agonism using functional calcium-flux assay. Out of 17 compounds evaluated, 14, 17, 19 and 25 exhibited good GPR40 agonistic activity with EC(50) values ranging from 0.07 to 8 microM (pEC(50) 7.12-5.09), respectively, with maximal agonistic response of 84-102%.