Sorgomol, germination stimulant for root parasitic plants, produced by Sorghum bicolor

A novel strigolactone sorgomol, germination stimulant for root parasitic plants Striga and Orobanche, was isolated and structure was elucidated. Sorgomol was more active on Striga than on Orobanche and may be the immediate precursor of sorgolactone in the biosynthetic pathway of strigolactones.     

Peagol and peagoldione, two new strigolactone-like metabolites isolated from pea root exudates

Two new strigolactone-like metabolites, named peagol and peagoldione, with germinative activity for root parasitic plants, were isolated from pea root exudates and were characterized by spectroscopic methods. Peagol was more active on Orobanche foetida and Phelipanche aegyptiaca seeds, while peagoldione was active on P. aegyptiaca only. Low activity was found on Orobanche crenata and Orobanche minor. Stimulatory activity of peagol on O. foetida seeds is most relevant as this species does not respond to the synthetic strigolactone analogue GR24, usually used as Orobanche germination standard.     

Stereoselective Synthesis and Biological Profile of All Stereoisomers of Lactam Analogues of Strigolactones GR24 and GR18

Strigolactones (SLs) are signaling molecules involved in plant development and governing interactions with soil microorganisms in the rhizosphere as well as the germination of parasitic weeds. Developing their use in Crop Protection is a promising approach to a sustainable agriculture by mitigating biotic and abiotic stresses. Recently, a new class of lactam analogues of SL has emerged, namely strigolactams, displaying outstanding potency to induce the germination of parasitic weed O. cumana as well as enhanced chemical and soil stability. Herein, we describe the stereoselective synthesis of GR24 and GR18 lactams harnessing the chemistry of chiral keteniminium (KI) salts, in particular the unprecedented reactivity of chloro-substituted KI, supported by DFT calculations. We disclose subsequently the biological activity on corn of the 32 stereopure strigolactams prepared, highlighting the crucial influence of stereochemistry and lactam substitution, rationalized by docking analyses. Finally, we performed stability studies in soil, which reveal that stereoisomers display very different half-lives, reflecting the significant impact of stereochemistry on degradation kinetics.     

Structure–Activity Relationship Assessment of Sophorolipid Ester Derivatives against Model Bacteria Strains

Sophorolipids (SLs) are glycolipids that consist of a hydrophilic sophorose head group covalently linked to a hydrophobic fatty acid tail. They are produced by fermentation of non-pathogenic yeasts such as Candida Bombicola. The fermentation products predominantly consist of the diacetylated lactonic form that coexists with the open-chain acidic form. A systematic series of modified SLs were prepared by ring opening of natural lactonic SL with n-alkanols of varying chain length under alkaline conditions and lipase-selective acetylation of sophorose primary hydroxyl groups. The antimicrobial activity of modified SLs against Gram-positive human pathogens was a function of the n-alkanol length, as well as the degree of sophorose acetylation at the primary hydroxyl sites. Modified SLs were identified with promising antimicrobial activities against Gram-positive human pathogens with moderate selectivity (therapeutic index, TI = EC₅₀/MIC_{B. cereus} = 6–33). SL-butyl ester exhibited the best antimicrobial activity (MIC = 12 μM) and selectivity (TI = 33) among all SLs tested. Kinetic studies revealed that SL-ester derivatives kill B. cereus in a time-dependent manner resulting in greater than a 3-log reduction in cell number within 1 h at 2×MIC. In contrast, lactonic SL required 3 h to achieve the same efficiency.     

Strigolactones,from Plants to Human Health: Achievements and Challenges

Strigolactones (SLs) are a class of sesquiterpenoid plant hormones that play a role in the response of plants to various biotic and abiotic stresses. When released into the rhizosphere, they are perceived by both beneficial symbiotic mycorrhizal fungi and parasitic plants. Due to their multiple roles, SLs are potentially interesting agricultural targets. Indeed, the use of SLs as agrochemicals can favor sustainable agriculture via multiple mechanisms, including shaping root architecture, promoting ideal branching, stimulating nutrient assimilation, controlling parasitic weeds, mitigating drought and enhancing mycorrhization. Moreover, over the last few years, a number of studies have shed light onto the effects exerted by SLs on human cells and on their possible applications in medicine. For example, SLs have been demonstrated to play a key role in the control of pathways related to apoptosis and inflammation. The elucidation of the molecular mechanisms behind their action has inspired further investigations into their effects on human cells and their possible uses as anti-cancer and antimicrobial agents.     

Suppression of Rice Cryptochrome 1b Decreases Both Melatonin and Expression of Brassinosteroid Biosynthetic Genes Resulting in Salt Tolerance

We investigated the relationship between the blue-light photoreceptor cryptochrome (CRY) and melatonin biosynthesis by generating RNA interference (RNAi) transgenic rice plants that suppress the cryptochrome 1b gene (CRY1b). The resulting CRY1b RNAi rice lines expressed less CRY1b mRNA, but not CRY1a or CRY2 mRNA, suggesting that the suppression is specific to CRY1b. The growth of CRY1b RNAi rice seedlings was enhanced under blue light compared to wild-type growth, providing phenotypic evidence for impaired CRY function. When these CRY1b RNAi rice plants were challenged with cadmium to induce melatonin, wild-type plants produced 100 ng/g fresh weight (FW) melatonin, whereas CRY1b RNAi lines produced 60 ng/g FW melatonin on average, indicating that melatonin biosynthesis requires the CRY photoreceptor. Due to possible feedback regulation, the expression of melatonin biosynthesis genes such as T5H, SNAT1, SNAT2, and COMT was elevated in the CRY1b RNAi lines compared to the wild-type plants. In addition, laminar angles decreased in the CRY1b RNAi lines via the suppression of brassinosteroid (BR) biosynthesis genes such as DWARF. The main cause of the BR decrease in the CRY1b RNAi lines seems to be the suppression of CRY rather than decreased melatonin because the melatonin decrease suppressed DWARF4 rather than DWARF.     

First synthesis of (±)-sorgomol, the germination stimulant for root parasitic weeds isolated from Sorghum bicolor

Sorgomol, isolated from Sorghum bicolor, is the germination stimulant for seeds of root parasitic weeds. The first synthesis of (±)-sorgomol has been achieved by starting from ethyl 2-oxocyclohexanecarboxylate.     

Synthetic disproof of the structure proposed for solanacol, the germination stimulant for seeds of root parasitic weeds

The structure proposed for solanacol, the germination stimulant for seeds of root parasitic weeds isolated from tobacco (Nicotiana tabacum L.), was synthesized. Comparison of the ¹H NMR data of the synthetic compounds with those reported for solanacol showed the previously proposed structure to be incorrect.     

Synthesis,Biological Evaluation,and Structure–Activity Relationships of 4-Aminopiperidines as Novel Antifungal Agents Targeting Ergosterol Biosynthesis

The aliphatic heterocycles piperidine and morpholine are core structures of well-known antifungals such as fenpropidin and fenpropimorph, commonly used as agrofungicides, and the related morpholine amorolfine is approved for the treatment of dermal mycoses in humans. Inspired by these lead structures, we describe here the synthesis and biological evaluation of 4-aminopiperidines as a novel chemotype of antifungals with remarkable antifungal activity. A library of more than 30 4-aminopiperidines was synthesized, starting from N-substituted 4-piperidone derivatives by reductive amination with appropriate amines using sodium triacetoxyborohydride. Antifungal activity was determined on the model strain Yarrowia lipolytica, and some compounds showed interesting growth-inhibiting activity. These compounds were tested on 20 clinically relevant fungal isolates (Aspergillus spp., Candida spp., Mucormycetes) by standardized microbroth dilution assays. Two of the six compounds, 1-benzyl-N-dodecylpiperidin-4-amine and N-dodecyl-1-phenethylpiperidin-4-amine, were identified as promising candidates for further development based on their in vitro antifungal activity against Candida spp. and Aspergillus spp. Antifungal activity was determined for 18 Aspergillus spp. and 19 Candida spp., and their impact on ergosterol and cholesterol biosynthesis was determined. Toxicity was determined on HL-60, HUVEC, and MCF10A cells, and in the alternative in vivo model Galleria mellonella. Analysis of sterol patterns after incubation gave valuable insights into the putative molecular mechanism of action, indicating inhibition of the enzymes sterol C14-reductase and sterol C8-isomerase in fungal ergosterol biosynthesis.     

Supercritical CO2 Extraction as a Tool to Isolate Anti-Inflammatory Sesquiterpene Lactones from Cichorium intybus L. Roots

Cichorium intybus L. or chicory plants are a natural source of health-promoting compounds in the form of supplements such as inulin, as well as other bioactive compounds such as sesquiterpene lactones (SLs). After inulin extraction, chicory roots are considered waste, with most SLs not being harnessed. We developed and optimized a new strategy for SL extraction that can contribute to the conversion of chicory root waste into valuable products to be used in human health-promoting applications. In our work, rich fractions of SLs were recovered from chicory roots using supercritical CO₂. A response surface methodology was used to optimize the process parameters (pressure, temperature, flow rate, and co-solvent percentage) for the extraction performance. The best operating conditions were achieved at 350 bar, 40 °C, and 10% EtOH as a co-solvent in a 15 g/min flow rate for 120 min. The extraction with supercritical CO₂ revealed to be more selective for the SLs than the conventional solid–liquid extraction with ethyl acetate. In our work, 1.68% mass and a 0.09% sesquiterpenes yield extraction were obtained, including the recovery of two sesquiterpene lactones (8-deoxylactucin and 11β,13-dihydro-8-deoxylactucin), which, to the best of our knowledge, are not commercially available. A mixture of the abovementioned compounds were tested at different concentrations for their toxic profile and anti-inflammatory potential towards a human calcineurin/NFAT orthologue pathway in a yeast model, the calcineurin/Crz1 pathway. The SFE extract obtained, rich in SLs, yielded results of inhibition of 61.74 ± 6.87% with 50 µg/mL, and the purified fraction containing 8-deoxylactucin and 11β,13-dihydro-8-deoxylactucin inhibited the activation of the reporter gene up to 53.38 ± 3.9% at 10 µg/mL. The potential activity of the purified fraction was also validated by the ability to inhibit Crz1 nuclear translocation and accumulation. These results reveal a possible exploitable green technology to recover potential anti-inflammatory compounds from chicory roots waste after inulin extraction.     

Synthesis and plant growth inhibitory activity of both enantiomers of pyricuol, a phytotoxin isolated from rice blast disease fungus Magnaporthe grisea

Both enantiomers and racemate of pyricuol, a phytotoxin isolated from the rice blast disease fungus, Magnaporthe grisea, have been synthesized by using Stille coupling and [2,3]-Wittig rearrangement reactions as the key steps. Both enantiomers induced dark necrotic lesions on rice leaves almost equally, but did not affect the growth of rice second leaf sheath and the germination of lettuce. Only natural enantiomer promoted the root growth of rice and lettuce.     

基于SRXRF和XANES研究Pb对玉米种子萌芽的影响及其分布和形态特征

以受不同浓度Pb胁迫下的玉米种子萌芽试验为基础,结合SRXRF研究Pb对玉米种子萌芽的影响和Pb在玉米种子的微区分布特征,利用X射线吸收近边结构技术(XANES)对萌芽玉米种子不同部位中Pb的化学形态进行分析,藉以了解种子对Pb的吸收和转化规律。结果表明,玉米种子的发芽率、根芽伸长量随培养溶液中Pb(NO3)2浓度增加而降低。种子发芽率、平均芽长、平均根长与暴露Pb浓度间的方差分析P-value分别为2.0×10!3,1.4×10!4和2.39×10!8,均小于0.01,为极显著差异,说明Pb胁迫对种子萌芽和根芽生长造成了极显著影响,且对根长抑制作用更大。SRXRF分析结果表明,种皮和胚结构是玉米种子富集Pb的主要部位,Pb富集在胚结构中将抑制种子萌芽。各种子样品的Pb-LⅢ(13035 eV)边XANES谱图相同,为同一种Pb形态,拟合结果显示其含74.3%的氯化磷酸铅和24.2%硬脂酸铅,说明Pb主要以氯化磷酸铅的形式沉积于玉米体内,并有少部分以与羧基结合的有机铅形式存在。     

Investigation of Antifungal Mechanisms of Thymol in the Human Fungal Pathogen,Cryptococcus neoformans

Due to lifespan extension and changes in global climate, the increase in mycoses caused by primary and opportunistic fungal pathogens is now a global concern. Despite increasing attention, limited options are available for the treatment of systematic and invasive mycoses, owing to the evolutionary similarity between humans and fungi. Although plants produce a diversity of chemicals to protect themselves from pathogens, the molecular targets and modes of action of these plant-derived chemicals have not been well characterized. Using a reverse genetics approach, the present study revealed that thymol, a monoterpene alcohol from Thymus vulgaris L., (Lamiaceae), exhibits antifungal activity against Cryptococcus neoformans by regulating multiple signaling pathways including calcineurin, unfolded protein response, and HOG (high-osmolarity glycerol) MAPK (mitogen-activated protein kinase) pathways. Thymol treatment reduced the intracellular concentration of Ca²⁺ by controlling the expression levels of calcium transporter genes in a calcineurin-dependent manner. We demonstrated that thymol decreased N-glycosylation by regulating the expression levels of genes involved in glycan-mediated post-translational modifications. Furthermore, thymol treatment reduced endogenous ergosterol content by decreasing the expression of ergosterol biosynthesis genes in a HOG MAPK pathway-dependent manner. Collectively, this study sheds light on the antifungal mechanisms of thymol against C. neoformans.     

Binding Free Energy (BFE) Calculations and Quantitative Structure–Activity Relationship (QSAR) Analysis of Schistosoma mansoni Histone Deacetylase 8 (smHDAC8) Inhibitors

Histone-modifying proteins have been identified as promising targets to treat several diseases including cancer and parasitic ailments. In silico methods have been incorporated within a variety of drug discovery programs to facilitate the identification and development of novel lead compounds. In this study, we explore the binding modes of a series of benzhydroxamates derivatives developed as histone deacetylase inhibitors of Schistosoma mansoni histone deacetylase (smHDAC) using molecular docking and binding free energy (BFE) calculations. The developed docking protocol was able to correctly reproduce the experimentally established binding modes of resolved smHDAC8–inhibitor complexes. However, as has been reported in former studies, the obtained docking scores weakly correlate with the experimentally determined activity of the studied inhibitors. Thus, the obtained docking poses were refined and rescored using the Amber software. From the computed protein–inhibitor BFE, different quantitative structure–activity relationship (QSAR) models could be developed and validated using several cross-validation techniques. Some of the generated QSAR models with good correlation could explain up to ~73% variance in activity within the studied training set molecules. The best performing models were subsequently tested on an external test set of newly designed and synthesized analogs. In vitro testing showed a good correlation between the predicted and experimentally observed IC₅₀ values. Thus, the generated models can be considered as interesting tools for the identification of novel smHDAC8 inhibitors.     

Kalihinols from two Acanthella cavernosa sponges: inhibitors of bacterial folate biosynthesis

Acanthella spp. sponges have been prolific sources of highly functionalized diterpene antibiotics. Two Acanthella cavernosa sponges were investigated based on the activity of their extracts in a screen designed to detect bacterial folate biosynthesis inhibitors. Bacillus subtilis PY79 strain harboring a lacZ reporter gene fusion to a trimethoprim-responsive promoter (PpanB) was used for the screen. The ability of kalihinols to inhibit bacterial folate biosynthesis was investigated resulting in preliminary structure activity relationships. Eight kalihinol type diterpenes were isolated from two Philippine Acanthella cavernosa specimens including two new 10- and 15-formamido-kalihinol F analogs.     

Sensitivity enhancement in capillary electrophoresis-mass spectrometry of anionic metabolites using a triethylamine-containing background electrolyte and sheath liquid

Analyte responses in CE‐ESI‐MS using negative ionization are frequently relatively low, thereby limiting sensitivity in metabolomics applications. In order to enhance the ionization efficiency of anionic metabolites, BGEs and sheath liquids (SLs) of various compositions were evaluated. Pressure‐induced infusion and CE‐MS experiments showed that addition of triethylamine (TEA) to the BGE and SL enhanced analyte intensities. A BGE consisting of 25 mM TEA (pH 11.7) and an SL of water–methanol (1:1, v/v) containing 5 mM TEA was selected, providing separation and detection of ten representative test metabolites with good reproducibility (migration time RSDs<1%) and linearity (R²>0.99). This BGE yielded lower limits of detection (0.7–9.1 μM) for most test compounds when compared with common CE‐MS methods using a BGE and SL containing ammonium acetate (NH₄Ac) (25 and 5 mM, respectively). CE‐MS of human urine revealed an average amount of 231 molecular features in negative ionization mode when TEA was used in the BGE and SL, whereas 115 and 102 molecular features were found with an NH₄Ac‐containing BGE and SL, employing a bare fused‐silica (BFS) and Polybrene‐dextran sulfate‐Polybrene (PB‐DS‐PB)‐coated capillary, respectively. With the CE‐MS method using TEA, about 170 molecular features were observed that were not detected with the NH₄Ac‐based CE‐MS methods. For more than 82% of the molecular features that were detected with the TEA as well as the NH₄Ac‐containg BGEs (i.e. common features), the peak intensities were higher using TEA with gain factors up to 7. Overall, the results demonstrate that BGEs and SLs containing TEA are quite favorable for the analysis of anionic metabolites in CE‐MS.     

Coumarin derivatives from Pedilanthus tithymaloides as inhibitors of conidial germination in Magnaporthe oryzae

In a screening for inhibitors of infection-related morphogenesis in the rice blast fungus Magnaporthe oryzae, a series of 10 coumarin derivatives were isolated from Pedilanthus tithymaloides (Euphorbiaceae). Seven of these compounds turned out to be known while three represent previously unreported natural products. Their structures were established on the basis of spectroscopic data and X-ray crystallography. Nine out of 10 coumarin derivatives were found to inhibit conidial germination in the phytopathogenic fungus at low concentrations.     

双层固相萃取-液相色谱/串联质谱法测定水稻中独脚金内酯

本文结合双层固相萃取和液相色谱-串联质谱法(LC-MS/MS),建立了水稻中内源性独角金内酯(Strigolactone,SLs)的快速分析方法。水稻根提取液经过石墨化炭黑/混合模式阴离子交换吸附剂+混合模式阳离子交换吸附剂(GCB/MAX+MCX)双层固相萃取柱除杂后,通过LC-MS/MS法分析检测。实验优化了固相萃取条件,并进行了方法学验证。结果表明,SLs在对应范围内线性关系良好(相关系数大于0.9972),方法检出限(S/N=3)为0.007~0.028ng/g,回收率为82.1%~115.8%,相对标准偏差(n=6)在1.9%~14.1%之间。建立的方法灵敏度高、重现性好,可用于水稻中内源性SLs的准确定量。