Analyzing the regulatory role of heat shock transcription factors in plant heat stress tolerance: a brief appraisal.

An increase in ambient temperature throughout the twenty-first century has been described as a "worldwide threat" for crop production. Due to their sessile lifestyles, plants have evolved highly sophisticated and complex heat stress response (HSR) mechanisms to respond to higher temperatures. The HSR allows plants to minimize the damages caused by heat stress (HS), thus enabling cellular protection. HSR is crucial for their lifecycle and yield, particularly for plants grown in the field. At the cellular level, HSR involves the production of heat shock proteins (HSPs) and other stress-responsive proteins to counter the negative effects of HS. The expression of most HSPs is transcriptionally regulated by heat shock transcription factors (HSFs). HSFs are a group of evolutionary conserved regulatory proteins present in all eukaryotes and regulate various stress responses and biological processes in plants. In recent years, significant progress has been made in deciphering the complex regulatory network of HSFs, and several HSFs not only from model plants but also from major crops have been functionally characterized. Therefore, this review explores the progress made in this fascinating research area and debates the further potential to breed thermotolerant crop cultivars through the modulation of HSF networks. Furthermore, we discussed the role of HSFs in plant HS tolerance in a class-specific manner and shed light on their functional diversity, which is evident from their mode of action. Additionally, some research gaps have been highlighted concerning class-specific manners.

Unfolding molecular switches in plant heat stress resistance: A comprehensive review.

KEY MESSAGE: Plant heat stress response is a multi-factorial trait that is precisely regulated by the complex web of transcription factors from various families that modulate heat stress responsive gene expression. Global warming due to climate change affects plant growth and development throughout its life cycle. Adds to this, the frequent occurrence of heat waves is drastically reducing the global crop yield. Molecular plant scientists can help crop breeders by providing genetic markers associated with stress resistance. Plant heat stress response (HSR), however, is a multi-factorial trait and using a single stress resistance trait might not be ideal to develop thermotolerant crops. Transcription factors participate in regulation of plant biological processes and environmental stress responses. Recent studies have revealed that plant HSR is precisely regulated by the complex web of transcription factors from various families. These transcription factors enhance plant heat stress tolerance by regulating the expression level of several stress-responsive genes independently or in cross talk with different other transcription factors. This review explores how signaling pathways triggered by heat stress are regulated by multiple transcription factor families. To our knowledge, we for the first time analyze the role of major transcription factor families in plant HSR along with their regulatory mechanisms. In the end, we will also discuss the potential of emerging technologies to improve thermotolerance in plants.

Molecular mechanisms of plant tolerance to heat stress: current landscape and future perspectives.

KEY MESSAGE: We summarize recent studies focusing on the molecular basis of plant heat stress response (HSR), how HSR leads to thermotolerance, and promote plant adaptation to recurring heat stress events. The global crop productivity is facing unprecedented threats due to climate change as high temperature negatively influences plant growth and metabolism. Owing to their sessile nature, plants have developed complex signaling networks which enable them to perceive changes in ambient temperature. This in turn activates a suite of molecular changes that promote plant survival and reproduction under adverse conditions. Deciphering these mechanisms is an important task, as this could facilitate development of molecular markers, which could be ultimately used to breed thermotolerant crop cultivars. In current article, we summarize mechanisms involve in plant heat stress acclimation with special emphasis on advances related to heat stress perception, heat-induced signaling, heat stress-responsive gene expression and thermomemory that promote plant adaptation to short- and long-term-recurring heat-stress events. In the end, we will discuss impact of emerging technologies that could facilitate the development of heat stress-tolerant crop cultivars.

Cis-trimethoxystilbene, exhibits higher genotoxic and antiproliferative effects than its isomer trans-trimethoxystilbene in MCF-7 and MCF-10A cell lines.

Stilbenes are a class of natural compounds with a wide variety of biological effects, such as antitumor activity. The best-known stilbene is resveratrol, whose clinical application is limited due to its low bioavailability. Methoxylated derivatives of this stilbene, including cis-trimethoxystilbene (cis-TMS) and trans-trimethoxystilbene (trans-TMS) have demonstrated more pronounced cytotoxic and anti-proliferative effects than resveratrol. Thus, the objective of this study is to evaluate and compare the cytotoxicity and antiproliferative effects of cis- and trans-TMS in MCF-7 and its normal counterpart MCF-10A. Both compounds were cytotoxic, genotoxic, and induced G2-M accumulation and cell death in the two cell lines. These results suggested that the genotoxicity of cis- and trans-TMS is involved in the reduction of cellular proliferation of MCF-7 and MCF-10A cells, but notably, such antiproliferative effects are more pronounced for cis- than trans-TMS.

Green chemistry appended synthesis, metabolic stability and pharmacokinetic assessment of medicinally important chromene dihydropyrimidinones.

A green chemistry approach has been developed for the synthesis of chromene dihydropyrimidinone (CDHPM) using recyclable Fe/Al pillared clay catalyst. Pharmacokinetic parameters like aqueous solubility, lipophilicity, P-glycoprotein (P-gp) ATPase activity, permeability, plasma protein binding, red blood cell (RBC) partitioning, metabolic stability in liver microsomes and in silico computations have been studied for the most potent anticancer chromene dihydropyrimidinone hybrid 1. This compound exhibited low solubility, optimum lipophilicity, no P-gp inhibitory activity, intermediate permeability, high plasma protein binding, low RBC partitioning, acceptable metabolic stability in rat liver microsomes (RLM) as well as human liver microsomes (HLM) with transitional hepatic extraction ratio.

Pharmacokinetics and Tissue Distribution of Aegeline after Oral Administration in Mice.

Aegeline is claimed to be a biologically active constituent of Aegle marmelos. Preclinical studies have reported possible therapeutic potential for aegeline against obesity and diabetes. In recent years, aegeline has been added to several weight loss products. However, the consumption of aegeline-containing supplements such as OxyELITE Pro and VERSA-1 has been linked to multiple cases of acute and chronic liver failure. This study was carried out to evaluate the pharmacokinetics and tissue distribution of aegeline in ND4 mice. Two doses of aegeline, a human equivalent dose (1×) 30 mg/kg and a 10× dose (300 mg/kg), were orally administered to the mice, and blood and tissue samples were collected over 8 h. The quantitative analysis of plasma and tissue homogenates (liver, kidney, and brain) was done by UHPLC-QTOF to determine aegeline concentrations. The peak plasma level of aegeline was achieved at a Tmax of 0.5 h, indicating its rapid absorption from the gastrointestinal tract. Aegeline was not detected in the plasma at 8 h after oral administration, with a half-life of 1.4 ± 0.01 and 1.3 ± 0.07 h for the 30 and 300 mg/kg doses, respectively. The half-life of aegeline in the liver was 1.2 h and 1.7 h for 30 and 300 mg/kg doses, respectively, with a Tmax of 1.9 h, which indicates relatively fast elimination of aegeline from the liver.

One-step, stereoselective synthesis of octahydrochromanes via the Prins reaction and their cannabinoid activities.

Novel, functionalized octahydrochromene derivatives were synthesized in a single step via the Prins reaction. Enantiomerically pure (+)-isopulegol was reacted with benzaldehyde to stereoselectively yield the corresponding octahydro-2H-chromen-4-ol derivative containing five stereocenters. A total of 10 compounds were synthesized by altering the enantiomer of isopulegol and the substituted benzaldehyde, and the resulting enantiopure octahydrochromenes were screened in vitro against the cannabinoid receptor isoforms CB1 and CB2. Compounds containing an olefin at the C4 position [(+)-3c, (-)-3c, (-)-7c, (-)-9c and (-)-11c] of the octahydrochromene scaffold were found to exhibit reasonable displacement of [3H] CP55,940 from the CB receptors, whereas the corresponding hydroxy analogs [(+)-3a, (+)-3b, (-)-3a, (-)-3b and (+)-5a] had very little or no effect.

Ameliorative effects of Trichosanthes dioica Extract in suppressing inflammatory mediators and attenuating oxidative stress.

The present study aimed to investigate the anti-inflammatory activity of the ethanolic extract of the aerial parts of Trichosanthes dioica and its successive fractions. The effect on oxidative stress involved in the pathogenesis of inflammation was evaluated. The ethanolic extract and its successive fractions were administered at a dose of 150 and 300 mg/kg b. w. for testing their anti-inflammatory activity by a carrageenan-induced edema model. The results showed that the ethyl acetate fraction exhibited significant potency against inflammation. Pertaining to mechanistic insight, the anti-inflammatory effect might be attributed to the attenuation in tumor necrosis factor-α level (ELISA assay) and reduced expression of cyclooxygenase-2 and nuclear transcription factor-κB (immunohistochemistry). The alleviation in oxidative stress has been pertinent to the elevation in the activities of antioxidant enzymes (superoxide dismutase, catalase, and glutathione) by active fractions. Furthermore, the ulcerogenic effect was insignificant even at a three times higher dose. Finally, it was concluded that the ethyl acetate fraction which showed significant biological potential against inflammation and oxidative stress could be viewed as a source of effective treatment.

Design, Synthesis, and Biological Evaluation of Thiazolidine-2,4-dione Conjugates as PPAR-γ Agonists.

A library of synthesized conjugates of phenoxy acetic acid and thiazolidinedione 5a-m showed potent peroxisome proliferator activated receptor-γ (PPAR-γ) transactivation as well as significant blood glucose lowering effect comparable to the standard drugs pioglitazone and rosiglitazone. Most of the compounds showed higher docking scores than the standard drug rosiglitazone in the molecular docking study. Compounds 5l and 5m exhibited PPAR-γ transactivation of 54.21 and 55.41%, respectively, in comparison to the standard drugs pioglitazone and rosiglitazone, which showed 65.94 and 82.21% activation, respectively. Compounds 5l and 5m significantly lowered the blood glucose level of STZ-induced diabetic rats. Compounds 5l and 5m lowered the AST, ALT, and ALP levels more than the standard drug pioglitazone. PPAR-γ gene expression was significantly increased by compound 5m (2.00-fold) in comparison to the standard drugs pioglitazone (1.5-fold) and rosiglitazone (1.0-fold). Compounds 5l and 5m did not cause any damage to the liver and could be considered as promising candidates for the development of new antidiabetic agents.

Novel benzenesulfonylureas containing thiophenylpyrazoline moiety as potential antidiabetic and anticancer agents.

In the present study a library of twenty six benzenesulfonylureas containing thiophenylpyrazoline moiety has been synthesized. All the compounds were docked against PPAR-γ target. Most of the compounds displayed higher dock score than standard drugs, glibenclamide and rosiglitazone. All the synthesized compounds were primarily evaluated for their antidiabetic effect by oral glucose tolerance test. Further assessment of antidiabetic potential of sixteen active compounds was then done on STZ induced diabetic model. The results of in vivo activity by both the methods were found to be consistent with each other as well as with docking studies. Change in body weight of STZ induced animals post treatment was also assessed at the end of study. In vitro PPAR-γ transactivation assay was performed on active compounds in order to validate docking results and the most active compound 3 k was also shown to elevate gene expression of PPAR-γ. Furthermore, the compounds were screened by National Cancer Institute, Bethesda for anticancer effect and two compounds 3h and 3 i were selected at one dose level since they exhibited sensitivity towards tumor cell lines (mainly melanoma).

Thiazolidine-2,4-diones derivatives as PPAR-γ agonists: synthesis, molecular docking, in vitro and in vivo antidiabetic activity with hepatotoxicity risk evaluation and effect on PPAR-γ gene expression.

A library of conjugates of chromones and 2,4-thiazolidinedione has been synthesized by Knoevenagel condensation followed by reduction using hydrogen gas and Pd/C as a catalyst. Compounds 5c and 5e were most effective in lowering the blood glucose level comparable to standard drug pioglitazone. Compound 5e exhibited potent PPAR-γ transactivation of 48.72% in comparison to pioglitazone (62.48%). All the molecules showed good glide score against the PPAR-γ target in molecular docking study. PPAR-γ gene expression was significantly increased by compound 5e (2.56-fold) in comparison to standard drug pioglitazone. Compounds 5e and 5c did not cause any damage to the liver and may be considered as promising candidates for the development of new antidiabetic agents.

Synthesis and evaluation of pyrazolines bearing benzothiazole as anti-inflammatory agents.

The present study aims at the synthesis of pyrazolines bearing benzothiazole and their evaluation as anti-inflammatory agents. The synthesized compounds were evaluated for their anti-inflammatory potential using carrageenan induced paw edema model. Two compounds 5a and 5d alleviated inflammation more than the standard drug celecoxib. Eight compounds 5 b, 5 c, 5 e, 5 g, 5 h, 6 b, 6 e and 6 f showed anti-inflammatory activity comparable to celecoxib. To understand the mode of action, COX-2 enzyme assay and TNF-α assay were carried out. All the active compounds were assessed for their cytotoxicity. The ulcerogenic risk evaluation was performed on the active compounds that were not found to be cytotoxic. Out of ten active compounds, two compounds (5 d and 6 f) were finally found to be the most potent anti-inflammatory agents attributing to the suppression of the COX-2 enzyme activity and TNF-α production without being either cytotoxic or ulcerogenic.

Decoding histone 3 lysine methylation: Insights into seed germination and flowering.

Histone lysine methylation is a highly conserved epigenetic modification across eukaryotes that contributes to creating different dynamic chromatin states, which may result in transcriptional changes. Over the years, an accumulated set of evidence has shown that histone methylation allows plants to align their development with their surroundings, enabling them to respond and memorize past events due to changes in the environment. In this review, we discuss the molecular mechanisms of histone methylation in plants. Writers, readers, and erasers of Arabidopsis histone methylation marks are described with an emphasis on their role in two of the most important developmental transition phases in plants, seed germination and flowering. Further, the crosstalk between different methylation marks is also discussed. An overview of the mechanisms of histone methylation modifications and their biological outcomes will shed light on existing research gaps and may provide novel perspectives to increase crop yield and resistance in the era of global climate change.

In-silico analysis and transformation of OsMYB48 transcription factor driven by CaMV35S promoter in model plant - Nicotiana tabacum L. conferring abiotic stress tolerance.

Global crop yield has been affected by a number of abiotic stresses. Heat, salinity, and drought stress are at the top of the list as serious environmental growth-limiting factors. To enhance crop productivity, molecular approaches have been used to determine the key regulators affecting stress-related phenomena. MYB transcription factors (TF) have been reported as one of the promising defensive proteins against the unfavorable conditions that plants must face. Different roles of MYB TFs have been suggested such as regulation of cellular growth and differentiation, hormonal signaling, mediating abiotic stress responses, etc. To gain significant insights, a comprehensive in-silico analysis of OsMYB TF was carried out in comparison with 21 dicot MYB TFs and 10 monocot MYB TFs. Their chromosomal location, gene structure, protein domain, and motifs were analyzed. The phylogenetic relationship was also studied, which resulted in the classification of proteins into four basic groups: groups A, B, C, and D. The protein motif analysis identified several conserved sequences responsible for cellular activities. The gene structure analysis suggested that proteins that were present in the same class, showed similar intron-exon structures. Promoter analysis revealed major cis-acting elements that were found to be responsible for hormonal signaling and initiating a response to abiotic stress and light-induced mechanisms. The transformation of OsMYB TF into tobacco was carried out using the Agrobacterium-mediated transformation method, to further analyze the expression level of a gene in different plant parts, under stress conditions. To summarize, the current studies shed light on the evolution and role of OsMYB TF in plants. Future investigations should focus on elucidating the functional roles of MYB transcription factors in abiotic stress tolerance through targeted genetic modification and CRISPR/Cas9-mediated genome editing. The application of omics approaches and systems biology will be indispensable in delineating the regulatory networks orchestrated by MYB TFs, facilitating the development of crop genotypes with enhanced resilience to environmental stressors. Rigorous field validation of these genetically engineered or edited crops is imperative to ascertain their utility in promoting sustainable agricultural practices.

Mechanistic insight into the protective effects of fisetin against arsenic-induced reproductive toxicity in male rats.

Arsenic is one of the most hazardous environmental contaminants, which adversely affects the dynamics of male reproductive system. Fisetin (FIS) is a bioactive flavonoid, which is known to exert strong antioxidative effects. Therefore, the current research was planned to evaluate the alleviative efficacy of FIS against arsenic-induced reproductive damages. Forty-eight male albino rats were divided into 4 groups (n = 12), which were treated as follows: (1) Control, (2) Arsenic-intoxicated group (8 mg kg-1), (3) Arsenic + FIS-treated group (8 mg kg-1 + 10 mg kg-1), and (4) FIS-treated group (10 mgkg-1). After 56 days of treatment, the biochemical, lipidemic, steroidogenic, hormonal, spermatological, apoptotic and histoarchitectural profiles of rats were analyzed. Arsenic intoxication reduced the enzymatic activities of catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione reductase (GSR), in addition to glutathione (GSH) level. Conversely, the levels of thiobarbituric acid reactive substance (TBARS) and reactive oxygen species (ROS) were increased. Moreover, it escalated the level of low-density lipoprotein (LDL), triglycerides and total cholesterol, while declining the level of high-density lipoprotein (HDL). Furthermore, steroidogenic enzymes expressions, 3ß-hydroxysteroid dehydrogenase (HSD), 17ß-HSD, steroidogenic acute regulatory protein (StAR), cholesterol side-chain cleavage enzyme (CYP11A1) and 17α-hydroxylase/17, 20-lyase (CYP17A1), were found to be reduced, which brought down the level of testosterone. Besides, the levels of gonadotropins (LH and FSH) were decreased. Additionally, a decline in sperm mitochondrial membrane potential (MMP), motility, epididymal sperm count and hypo-osmotic swelling (HOS) coil-tailed sperms was observed, whereas the dead sperms and structural damages (head, midpiece and tail) of sperms were escalated. Moreover, arsenic exposure up-regulated the mRNA expressions of apoptotic markers, namely Bax and caspase-3, whereas lowered the expression of anti-apoptotic marker, Bcl-2. In addition, it induced histoarchitectural changes in testes of rats. However, FIS treatment resulted in remarkable improvements in testicular and sperm parameters. Therefore, it was inferred that FIS could serve as a therapeutic candidate against arsenic-generated male reproductive toxicity attributing to its anti-oxidant, anti-lipoperoxidative, anti-apoptotic, and androgenic efficacy.

Synthesis of some new s-alkylated 1,2,4-triazoles, their mannich bases and their biological activities.

A series of 1-(4-methoxyphenyl)-2-[5-{(biphenyl-4-yloxy)methyl}4-(substituted phenyl)-3-mercapto-(4H)-1,2,4-triazol-3-ylthio)] ethanones (6a-6s) and 4-(substituted phenyl)-3-(morpholin/pyrrolidin-4-ylmethylthio)-5-(4-phenylphenoxymethyl)-4H-1,2,4-triazoles (7a-7e) were synthesized in order to obtain new compounds with potent anti-inflammatory and analgesic activity with insignificant ulceration. Among the synthesized compounds, (6c), (6e), (6g) and (6l) from triazole series and (7b) and (7e) from Mannich base series were found to exhibit significant anti-inflammatory activity with 59.69, 59.69, 64.69, 79.84, 54.54, 79.69% and 52.55, 57.50, 72.52, 83.03, 60.06, 84.08% inhibition of paw edema at 3 h and 5 h respectively, in comparison to the standard drug ibuprofen (78.93 and 82.58% at 3 h and 5 h). The active compounds were further tested for their analgesic activity and gastric ulceration study. Compounds 6g, 7b and 7e exhibited significant analgesic activity with reaction time (3.60, 3.22, 3.88 s) respectively at 60 min. without causing any gastric irritation. These compounds were also screened for their in vitro antimicrobial activity, Compounds 6f, 6g, 6h, 6l, 6o, 6p, 7a, 7b and 7c showed significant zone of inhibition against various antimicrobial stains. It is concluded that the compounds 6g, 7b and 7e possess a good spectrum of activities. Compound 7e may be considered potent for development of better anti-inflammatory agent. The antimicrobial activity revealed that most of the compounds showed moderate to significant activity. Compounds containing nitro, chloro, bromo and fluoro group showing better activity. All the compounds from 7a, 7b and 7e were active against gram positive bacteria (S. aureus).

Balancing the efficacy vs. the toxicity of promiscuous natural products: Paclitaxel-based acid-labile lipophilic prodrugs as promising chemotherapeutics.

TumorSelect® is an anticancer technology that combines cytotoxics, nanotechnology, and knowledge of human physiology to develop innovative therapeutic interventions with minimal undesirable side effects commonly observed in conventional chemotherapy. Tumors have a voracious appetite for cholesterol which facilitates tumor growth and fuels their proliferation. We have transformed this need into a stealth delivery system to disguise and deliver anticancer drugs with the assistance of both the human body and the tumor cell. Several designer prodrugs are incorporated within pseudo-LDL nanoparticles, which carry them to tumor tissues, are taken up, internalized, transformed into active drugs, and inhibit cancer cell proliferation. Highly lipophilic prodrug conjugates of paclitaxel suitable for incorporation into the pseudo-LDL nanoparticles of the TumorSelect® delivery vehicle formulation were designed, synthesized, and evaluated in the panel of 24-h NCI-60 human tumor cell line screening to demonstrate the power of such an innovative approach. Taxane prodrugs, viz., ART-207 was synthesized by tethering paclitaxel to lipid moiety with the aid of a racemic solketal as a linker in cost-effective, simple, and straightforward synthetic transformations. In addition to the typical 24-h NCI screening protocol, these compounds were assessed for growth inhibition or killing of ovarian cell lines for 48 and 72h-time intervals and identified the long-lasting effectiveness of these lipophilic prodrugs. All possible, enantiomerically pure isomers of ART-207 were also synthesized, and cytotoxicities were biosimilar to racemic ART-207, suggesting that enantiopurity of linker has a negligible effect on cell proliferation. To substantiate further, ART-207 was evaluated for its in vivo tumor reduction efficacy by studying the xenograft model of ovarian cancer grown in SCID mice. Reduced weight loss (a measure of toxicity) in the ART-207 group was observed, even though it was dosed at 2.5x the paclitaxel equivalent of Abraxane®. As a result, our delineated approach is anticipated to improve patient quality of life, patient retention in treatment regimes, post-treatment rapid recovery, and overall patient compliance without compromising the efficacy of the cytotoxic promiscuous natural products.

Utility of fatty acid profile and in vitro immune cell activation for chemical and biological standardization of Arthrospira/Limnospira.

Commercially cultivated Limnospira (species formerly classified to genus Arthrospira) is a popular food/supplement consumed by millions of people worldwide for health benefits. The objective of the current research was to advance the standardization technology for Limnospira. Quantitative methods were established to detect fatty acids as potential chemical markers and immune-enhancing activity. Analysis of 20 different batches of biomass obtained from one commercial grower demonstrated that there was a statistically significant relationship between the sum of two fatty acids (linoleic and γ-linolenic) and Toll-like receptor (TLR)2/TLR1-dependent activation (R2 = 0.48, p = 0.0007). Investigation of 12 biomass samples sourced from growers in 10 different countries demonstrated that fatty acid content was again significantly correlated with biological activity (R2 = 0.72, p = 0.0005) and the content of fatty acids varied by twofold and activity by 12.5-fold. This large variation between different samples confirms the need to use the present standardization methods to ensure consistent and properly characterized biomass for consumers and for future scientific research.

Computational Tools to Expedite the Identification of Potential PXR Modulators in Complex Natural Product Mixtures: A Case Study with Five Closely Related Licorice Species.

The genus Glycyrrhiza, comprising approximately 36 spp., possesses complex structural diversity and is documented to possess a wide spectrum of biological activities. Understanding and finding the mechanisms of efficacy or safety for a plant-based therapy is very challenging, yet it is crucial and necessary to understand the polypharmacology of traditional medicines. Licorice extract was shown to modulate the xenobiotic receptors, which might manifest as a potential route for natural product-induced drug interactions. However, different mechanisms could be involved in this phenomenon. Since the induced herb-drug interaction of licorice supplements via Pregnane X receptor (PXR) is understudied, we ventured out to analyze the potential modulators of PXR in complex mixtures such as whole extracts by applying computational mining tools. A total of 518 structures from five species of Glycyrrhiza: 183 (G. glabra), 180 (G. uralensis), 100 (G. inflata), 33 (G. echinata), and 22 (G. lepidota) were collected and post-processed to yield 387 unique compounds. Visual inspection of top candidates with favorable ligand-PXR interactions and the highest docking scores were identified. The in vitro testing revealed that glabridin (GG-14) is the most potent PXR activator among the tested compounds, followed by licoisoflavone A, licoisoflavanone, and glycycoumarin. A 200 ns molecular dynamics study with glabridin confirmed the stability of the glabridin-PXR complex, highlighting the importance of computational methods for rapid dereplication of potential xenobiotic modulators in a complex mixture instead of undertaking time-consuming classical biological testing of all compounds in a given botanical.

Novel Machaeriol Analogues as Modulators of Cannabinoid Receptors: Structure-Activity Relationships of (+)-Hexahydrocannabinoids and Their Isoform Selectivities.

Machaeriols are an important class of compounds that structurally resemble tetrahydrocannabinol (Δ9-THC), with the major differences being inverted stereochemistry at the ring junction as [6aR, 10aR] and an additional stereocenter at the C9 position of the A-ring due to saturation. A previous study reported that machaeriols did not show any cannabinoid receptor activity, even though these hexahydrodibenzopyran analogues mimic a privileged (+)-tetrahydrocannabinoid scaffold. To unravel structural requisites for modulation of cannabinoid receptors, a simple late-stage divergent approach was undertaken to functionalize the machaeriol scaffold using the Suzuki coupling reaction. Fourteen hexahydro analogues were synthesized and screened against both cannabinoid receptor isoforms, CB1 and CB2. Interestingly, many of the analogues showed a significant binding affinity for both receptors; however, two analogues, 11H and 11J, were identified as possessing CB2 receptor-selective functional activity in the GTPγS assay; they were found to be micromolar-range agonists, with EC50 values of 5.7 and 16 µM, respectively. Furthermore, molecular dynamics simulations between the CB2 receptor and two novel analogues resulted in unique interaction profiles by tightly occupying the active ligand-binding domain of the CB2 receptor and maintaining stable interactions with the critical residues Phe94, Phe281, and Ser285. For the first time, with the aid of structure-activity relationships of (+)-hexahydrocannabinoids, CB2 selective agonists were identified with late-stage diversification using palladium-mediated C-C bond formation. By simply switching to (R)-citronellal as a chiral precursor, enantiomerically pure (-)-hexahydrocannabinoids with better CB1/CB2 receptor isoform selectivity can be obtained using the current synthetic approach.