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Half the world's population is at risk of developing a malaria infection, which is caused by parasites of the genus Plasmodium . Currently, resistance has been identified to all clinically available antimalarials, highlighting an urgent need to develop novel compounds and better understand common mechanisms of resistance. We previously identified a novel tetrahydro-β-carboline compound, PRC1590, which potently kills the malaria parasite. To better understand its mechanism of action, we selected for and characterized resistance to PRC1590 in Plasmodium falciparum . Through in vitro selection of resistance to PRC1590, we have identified that a single-nucleotide polymorphism on the parasite's multidrug resistance protein 1 (PfMDR1 G293V) mediates resistance to PRC1590. This mutation results in stereospecific resistance and sensitizes parasites to other antimalarials, such as mefloquine, quinine, and MMV019017. Intraerythrocytic asexual stage specificity assays have revealed that PRC1590 is most potent during the trophozoite stage when the parasite forms a single digestive vacuole (DV) and actively digests hemoglobin. Moreover, fluorescence microscopy revealed that PRC1590 disrupts the function of the DV, indicating a potential molecular target associated with this organelle. Our findings mark a significant step in understanding the mechanism of resistance and the mode of action of this emerging class of antimalarials. In addition, our results suggest a potential link between resistance mediated by PfMDR1 and PRC1590's molecular target. This research underscores the pressing need for future research aimed at investigating the intricate relationship between a compound's chemical scaffold, molecular target, and resistance mutations associated with PfMDR1.

Calophyllum tomentosum belonging to Clusiaceae family is an Indian medicinal plant used as folklore medicine to cure various kinds of diseases reported in Ayurveda, and the leaves of the plant are also used as an active ingredient for the preparation of a botanical medicine known as 'Punnaga', 'Surapunnaga' and 'Tamoil' among other common names. Chemical profiling of the methanol extract of the defatted leaf revealed the presence of amentoflavone (1) as one of the constituents along with coumarins, terpenoids, steroids, and apetalic acids. Structural determination of amentoflavone (1) has been conducted by chemical, spectral, and spectrometric methods in comparison with spectral values available in the literature and confirmed by a single crystal X-ray diffraction study. Amentoflavone (1) and its derivative (2-5) tested to check the efficacy of anti-malarial activity against Plasmodium falciparum. Amongst them, only tetra methoxy amentoflavone, (2) exhibited moderate anti-malarial activity with IC 50 value 1.99±0.42 μM against Plasmodium falciparum in comparison with artemisinin as control, whereas the other products possessed almost negligible activity although their structural skeletons are identical with little variation of number and nature of substituents. The structure activity relationship (SAR) of the active constituent and its derivatives is reported herein., (© 2024 Wiley-VHCA AG, Zurich, Switzerland.)

The development of parasite resistance to both artemisinin derivatives and their partner drugs jeopardizes the effectiveness of the artemisinin combination therapy. Thus, the discovery of new antimalarial drugs, with new mechanisms of action, is urgently needed. We recently disclosed that β-carboline 1a was orally efficacious in Plasmodium berghei -infected mice and that it showed low cross-resistance between susceptible Plasmodium falciparum and four different drug-resistant strains. In this report, we describe the synthesis and in vitro antimalarial evaluation of 91 new derivatives of 1a . The asexual blood stage growth inhibition data show a clear preference for a 3,4-dihalogenated, 3,5-dihalogenated, 3,4,5-trichloro-, or 4-trifluoromethyphenyl ring at the C1-position. The most potent compound, 3,4,5-trichlorophenyl-substituted 42a , is twice as potent as 1a . Six potent analogues were assessed for their drug-like properties, and four of these were subjected to in vitro barcoded cross-resistance profiling. Compounds 1a , 1m , 42a , and 42m showed no cross-resistance to 32 resistance mutations on the Dd2 genetic background and 10 resistance mutations on the 3D7 genetic background. These data suggest that compounds in this scaffold possess a novel mechanism of antimalarial action.

Dolichols are isoprenoid end-products of the mevalonate and 2 C -methyl-D-erythritol-4-phosphate pathways. The synthesis of dolichols is initiated with the addition of several molecules of isopentenyl diphosphate to farnesyl diphosphate. This reaction is catalyzed by a cis -prenyltransferase and leads to the formation of polyprenyl diphosphate. Subsequent steps involve the dephosphorylation and reduction of the α-isoprene unit by a polyprenol reductase, resulting in the generation of dolichol. The size of the dolichol varies, depending on the number of isoprene units incorporated. In eukaryotes, dolichols are synthesized as a mixture of four or more different lengths. Their biosynthesis is predicted to occur in the endoplasmic reticulum, where dolichols play an essential role in protein glycosylation. In this study, we have developed a selection of aptamers targeting dolichols and enhanced their specificity by incorporating fatty acids for negative selection. One aptamer showed high enrichment and specificity for linear polyisoprenoids containing at least one oxygen atom, such as an alcohol or aldehyde, in the α-isoprene unit. The selected aptamer proved to be a valuable tool for the subcellular localization of polyisoprenoids in the malaria parasite. To the best of our knowledge, this is the first time that polyisoprenoids have been localized within a cell using aptamer-based imaging techniques.

Cripowellins from Crinum erubescens are known pesticidal and have potent antiplasmodial activity. To gain mechanistic insights to this class of natural products, studies to determine the timing of action of cripowellins within the asexual intraerythrocytic cycle of Plasmodium falciparum were performed and led to the observation that this class of natural products induced reversible cytostasis in the ring stage within the first 24 h of treatment. The transcriptional program necessary for P. falciparum to progress through the asexual intraerythrocytic life cycle is well characterized. Whole transcriptome abundance analysis showed that cripowellin B "pauses" the transcriptional program necessary to progress through the intraerythrocytic life cycle coinciding with the lack of morphological progression of drug treated parasites. In addition, cripowellin B-treated parasites re-enter transcriptional progression after treatment was removed. This study highlights the use of cripowellins as chemical probes to reveal new aspects of cell cycle progression of the asexual ring stage of P. falciparum which could be leveraged for the generation of future antimalarial therapeutics.

The tetrahydro-β-carboline scaffold has proven fertile ground for the discovery of antimalarial agents (e.g., MMV008138 ( 1 ) and cipargamin ( 2 )). Similarity searching of a publicly disclosed collection of antimalarial hits for molecules resembling 1 drew our attention to N2-acyl tetrahydro-β-carboline GNF-Pf-5009 ((±)- 3b ). Compound purchase, "analog by catalog", and independent synthesis of hits indicated the benzofuran-2-yl amide portion was required for in vitro efficacy against P. falciparum . Preparation of pure enantiomers demonstrated the pharmacological superiority of ( R )- 3b . Synthesis and evaluation of D- and F-ring substitution variants and benzofuran isosteres indicated a clear structure-activity relationship. Ultimately ( R )- 3b was tested in Plasmodium berghei -infected mice; unfavorable physicochemical properties may be responsible for the lack of oral efficacy., Competing Interests: The authors declare no competing financial interest., (© 2022 American Chemical Society.)

Virtual ligand screening of a publicly available database of antimalarial hits using a pharmacophore derived from antimalarial MMV008138 identified TCMDC-140230, a tetrahydro-β-carboline amide, as worthy of exploration. All four stereoisomers of this structure were synthesized, but none potently inhibited growth of the malaria parasite Plasmodium falciparum . Interestingly, 7e , a minor byproduct of these syntheses, proved to be potent in vitro against P. falciparum and was orally efficacious (40 mg/kg) in an in vivo mouse model of malaria., Competing Interests: The authors declare no competing financial interest., (© 2022 American Chemical Society.)

Humans have significantly altered the energy balance of the Earth's climate system mainly not only by extracting and burning fossil fuels but also by altering the biosphere and using halocarbons. The 3rd US National Climate Assessment pointed to a need for a system of indicators of climate and global change based on long-term data that could be used to support assessments and this led to the development of the National Climate Indicators System (NCIS). Here we identify a representative set of key atmospheric indicators of changes in atmospheric radiative forcing due to greenhouse gases (GHGs), and we evaluate atmospheric composition measurements, including non-CO 2 GHGs for use as climate change indicators in support of the US National Climate Assessment. GHG abundances and their changes over time can provide valuable information on the success of climate mitigation policies, as well as insights into possible carbon-climate feedback processes that may ultimately affect the success of those policies. To ensure that reliable information for assessing GHG emission changes can be provided on policy-relevant scales, expanded observational efforts are needed. Furthermore, the ability to detect trends resulting from changing emissions requires a commitment to supporting long-term observations. Long-term measurements of greenhouse gases, aerosols, and clouds and related climate indicators used with a dimming/brightening index could provide a foundation for quantifying forcing and its attribution and reducing error in existing indicators that do not account for complicated cloud processes., Competing Interests: Conflict of interestThe authors declare no competing interests., (© This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply 2021.)

The antimalarial candidate MMV008138 (1a) is of particular interest because its target enzyme (IspD) is absent in human. To achieve higher potency, and to probe for steric demand, a series of analogs of 1a were prepared that featured methyl-substitution of the B- and C-rings, as well as ring-chain transformations. X-ray crystallography, NMR spectroscopy and calculation were used to study the effects of these modifications on the conformation of the C-ring and orientation of the D-ring. Unfortunately, all the B- and C-ring analogs explored lost in vitro antimalarial activity. The possible role of steric effects and conformational changes on target engagement are discussed., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Unique lindenane sesquiterpenoid dimers from Chloranthecae spp. were recently identified with promising in vitro antiplasmodial activity and potentially novel mechanisms of action. To gain mechanistic insights to this new class of natural products, in vitro selection of Plasmodium falciparum resistance to the most active antiplasmodial compound, chlorajaponilide C, was explored. In all selected resistant clones, the half-maximal effective concentration (EC 50 ) of chlorajaponilide C increased >250-fold, and whole genome sequencing revealed mutations in the recently discovered P. falciparum prodrug activation and resistance esterase (PfPARE). Chlorajaponilide C was highly potent (mean EC 50 = 1.6 nM, n = 34) against fresh Ugandan P. falciparum isolates. The analysis of the structure-resistance relationships revealed that in vitro potency of a subset of lindenane sesquiterpenoid dimers was not mediated by PfPARE mutations. Thus, chlorajaponilide C, but not some related compounds, required parasite esterase activity for in vitro potency, and those compounds serve as the foundation for development of potent and selective antimalarials.

Malaria continues to be one of the deadliest diseases worldwide, and the emergence of drug resistance parasites is a constant threat. Plasmodium parasites utilize the methylerythritol phosphate (MEP) pathway to synthesize isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP), which are essential for parasite growth. Previously, we and others identified that the Malaria Box compound MMV008138 targets the apicoplast and that parasite growth inhibition by this compound can be reversed by supplementation of IPP. Further work has revealed that MMV008138 targets the enzyme 2- C-methyl-d-erythritol 4-phosphate cytidylyltransferase (IspD) in the MEP pathway, which converts MEP and cytidine triphosphate (CTP) to cytidinediphosphate methylerythritol (CDP-ME) and pyrophosphate. In this work, we sought to gain insight into the structure-activity relationships by probing the ability of MMV008138 analogs to inhibit PfIspD recombinant enzyme. Here, we report PfIspD inhibition data for fosmidomycin (FOS) and 19 previously disclosed analogs and report parasite growth and PfIspD inhibition data for 27 new analogs of MMV008138. In addition, we show that MMV008138 does not target the recently characterized human IspD, reinforcing MMV008138 as a prototype of a new class of species-selective IspD-targeting antimalarial agents.

Pretreatment with ionic liquids (IL) such as 1-ethyl-3-methylimidazolium chloride or acetate is an effective method for aiding deconstruction of lignocellulosic biomass; however, the residual IL remaining in hydrolysates can be inhibitory to growth of ethanologenic or oleaginous yeasts that have been examined in the literature. The aim of this study was to identify oleaginous yeasts that are tolerant of the IL [C 2 C 1 Im][OAc] and [C 2 C 1 Im]Cl using 45 strains belonging to 38 taxonomically diverse species within phyla Ascomycota and Basidiomycota. Yeasts were cultivated in laboratory medium supplemented with 0, 2, or 4% IL in 96-well plates. The eight most tolerant strains were then cultivated in 10-mL media with no IL, 242mM [C 2 C 1 Im][OAc], or 242mM [C 2 C 1 Im]Cl. The effects of [C 2 C 1 Im] + exposure on cell mass production and lipid accumulation varied at the species and strain level. The acetate salt decreased cell biomass and lipid production more severely than did the chloride ion for six strains. Lipid output was not markedly different (2.1 vs. 2.3 g/L) in Yarrowia lipolytica UCDFST 51-30, but decreased from 5 to 65% in other yeasts. An equimolar concentration of the chloride salt resulted in much milder effects, from 25% decrease to 66% increase in lipid output. The highest lipid outputs in this media were 8.3 and 7.9 g/L produced by Vanrija humicola UCDFST 10-1004 and UCDFST 12-717, respectively. These results demonstrated substantial lipid production in the presence of [C 2 C 1 Im]Cl at concentrations found in lignocellulosic hydrolysates, and thus, these two strains are ideal candidates for further investigation.

Antiplasmodial bioassay guided fractionation of a Madagascar collection of Crinum firmifolium led to the isolation of seven compounds. Five of the seven compounds were determined to be 2-alkylquinolin-4(1H)-ones with varying side chains. Compounds 1 and 4 were determined to be known compounds with reported antiplasmodial activities, while 5 was believed to be a new branched 2-alkylquinolin-4(1H)-one, however, it was isolated in limited quantities and in admixture and therefore was synthesized to confirm its structure as a new antiplasmodial compound. Along with 5, two other new and branched compounds 6 and 7 were synthesized as well. Accompanying the five quinolones were two known compounds 2 and 3 which are inactive against Plasmodium falciparum. The isolation, structure elucidation, total synthesis, and biological evaluation of these compounds are discussed in this article., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Ambient levels and variability of major atmospheric halocarbons, i.e. CFC-12, CFC-11, CFC-113, CCl4, CH3CCl3, C2HCl3, and C2Cl4 in a major metropolis (Taipei, Taiwan) were re-investigated after fourteen years by flask sampling in 2012. Our data indicates that the variability expressed as standard deviations (SD) of CFC-113 and CCl4 remained small (2.0 ppt and 1.9 ppt, respectively) for the 10th-90th percentile range in both sampling periods; whereas the variability of CFC-12, CFC-11, C2HCl3, and C2Cl4 measured in 2012 became noticeably smaller than observed in 1998, suggesting their emissions were reduced over time. By comparing with the background data of a global network (NOAA/ESRL/GMD baseline observatories), the ambient levels and distribution of these major halocarbons in Taipei approximated those at a background site (Mauna Loa) in 2012, suggesting that the fingerprint of the major halocarbons in a used-to-be prominent source area has gradually approached to that of the background atmosphere., (Copyright © 2015 Elsevier Ltd. All rights reserved.)