Chromatography with silver nitrate

Essential oil and furanosesquiterpenes from myrrh oleo-gum resin: a breakthrough in mosquito vector management

Mosquitoes (Diptera: Culicidae) are vectors of various pathogens of public health concern and replacing conventional insecticides remains a challenge. In this regard, natural products represent valuable sources of potential insecticidal compounds, thus increasingly attracting research interest. Commiphora myrrha (T.Nees) Engl. (Burseraceae) is a medicinal plant whose oleo-gum resin is used in food, cosmetics, fragrances, and pharmaceuticals. Herein, the larvicidal potential of its essential oil (EO) was assessed on four mosquito species (Aedes albopictus Skuse, Aedes aegypti L., Anopheles gambiae Giles and Anopheles stephensi Liston), with LC50 values ranging from 4.42 to 16.80 μg/mL. The bio-guided EO fractionation identified furanosesquiterpenes as the main larvicidal compounds. A GC-MS-driven untargeted metabolomic analysis revealed 32 affected metabolic pathways in treated larvae. The EO non-target toxicity on Daphnia magna Straus (LC50 = 4.51 μL/L) and its cytotoxicity on a human kidney cell line (HEK293) (IC50 of 14.38 μg/mL) were also assessed. This study shows the potential of plant products as innovative insecticidal agents and lays the groundwork for the possible exploitation of C. myrrha EO in sustainable approaches for mosquito management.

Differentiation of Δ9-THC and CBD Using Silver-Ligand Ion Complexation and Electrospray Ionization Tandem Mass Spectrometry (ESI-MS/MS)

The 2018 Farm Bill defines marijuana as Cannabis sativa L. or any derivative thereof that contains greater than 0.3% Δ9-tetrahydrocannabinol (Δ9-THC) on a dry weight basis. The main cannabinoids present in Cannabis sativa L., Δ9-THC and cannabidiol (CBD), are structural isomers that cannot be differentiated using direct mass spectrometry with soft ionization techniques alone. Due to the classification of marijuana as a Schedule I controlled substance, the differentiation of Δ9-THC and CBD is crucial within the seized drug community. This study explores the use of Ag-ligand ion complexation and electrospray ionization tandem mass spectrometry (ESI-MS/MS) for the differentiation of Δ9-THC and CBD using six different Ag complexes. Differences between the binding affinities of Δ9-THC and CBD for [Ag(PPh3)(OTf)]2 lead to the formation of unique product ions at m/z 421/423, m/z 353/355, and m/z 231 for CBD, enabling the differentiation of CBD from Δ9-THC. When applied to the analysis of known Δ9-THC:CBD mixture ratios, the developed [Ag(PPh3)(OTf)]2 ion complexation method was able to differentiate Δ9-THC-rich and CBD-rich samples based on the average abundance of the product ions at m/z 421/423. The developed approach was then applied to methanolic extracts of 20 authentic cannabis samples with known Δ9-THC and CBD compositions, resulting in a 95% correct classification rate. Even though the developed Ag-ligand ion complexation method was only demonstrated for the qualitative differentiation of Δ9-THC-rich and CBD-rich cannabis, this study establishes a foundation for the use of Ag-ligand ion complexation that is essential for future quantitative approaches.

Plasmalogens: Free Radical Reactivity and Identification of Trans Isomers Relevant to Biological Membranes

Plasmalogens are membrane phospholipids with two fatty acid hydrocarbon chains linked to L-glycerol, one containing a characteristic cis-vinyl ether function and the other one being a polyunsaturated fatty acid (PUFA) residue linked through an acyl function. All double bonds in these structures display the cis geometrical configuration due to desaturase enzymatic activity and they are known to be involved in the peroxidation process, whereas the reactivity through cis-trans double bond isomerization has not yet been identified. Using 1-(1Z-octadecenyl)-2-arachidonoyl-sn-glycero-3-phosphocholine (C18 plasm-20:4 PC) as a representative molecule, we showed that the cis-trans isomerization can occur at both plasmalogen unsaturated moieties, and the product has characteristic analytical signatures useful for omics applications. Using plasmalogen-containing liposomes and red blood cell (RBC) ghosts under biomimetic Fenton-like conditions, in the presence or absence of thiols, peroxidation, and isomerization processes were found to occur with different reaction outcomes due to the particular liposome compositions. These results allow gaining a full scenario of plasmalogen reactivity under free radical conditions. Moreover, clarification of the plasmalogen reactivity under acidic and alkaline conditions was carried out, identifying the best protocol for RBC membrane fatty acid analysis due to their plasmalogen content of 15-20%. These results are important for lipidomic applications and for achieving a full scenario of radical stress in living organisms.

Total Synthesis of Caldorazole, a Potent Mitochondrial Respiratory Chain Inhibitor without Chiral Centers

Caldorazole (1) is a novel polyketide that was isolated from a marine cyanobacterium in 2022. It is a unique natural product that exhibits potent inhibitory activity against mitochondrial respiratory chain complex I despite having no chiral centers. To establish a method for obtaining caldorazole without relying on biological resources and for constructing a useful synthetic route for studies of its structure-activity relationship, we achieved the first total synthesis of caldorazole using a convergent synthetic route.

Synthesis of obtusifoliol and analogues as CYP51 substrates

Sterol 14α-demethylases (CYP51s) are a ubiquitous superfamily of cytochrome P450 enzymes that play an essential role in sterol biosynthesis. As fungal CYP51s are the target of azole-based antifungal agents, which are facing the problem of increasing resistance, the substrate specificity of this enzyme subclass has recently garnered significant attention. Herein we report the first chemical synthesis of the final endogenous substrate of this enzyme class, obtusifoliol, in 1.3% yield across ten steps from a commercially available lanosterol mixture. Intermediates along this pathway provide a basis for further derivatisation of the sterol skeleton and future investigation into CYP51 inhibition to overcome pathogens' azole resistance.

Separation of menaquinone-7 geometric isomers by semipreparative high-performance liquid chromatography with silver complexation and identification by nuclear magnetic resonance

Dietary supplements containing vitamin K2 are often used to prevent osteoporosis, vascular calcification and coronary heart disease. It has been shown that some of these products contain a mixture of menaquinone-7 geometric isomers. Since the geometric shape may influence biological activity, there was a need for a semipreparative method to isolate single compounds for further studies. Here, we present an argentation chromatographic method for the separation of menaquinone-7 isomers and an nuclear magnetic resonance (NMR) methodology for the configuration assignment of isoprenoid side chain. The DFT calculations were performed to determine more energetically favorable complexes between the cis or trans menaquinone-7 isomers and the silver cation. Seventeen components were resolved, and fractions were collected and subjected to NMR study. Structures and chemical shifts for thirteen new compounds were assigned, and the identity of three known compounds was confirmed.

Synthesis of 12β-Methyl-18-nor-bile Acids

Decoupling the roles of the farnesoid X nuclear receptor and Takeda G-protein-coupled bile acid receptor 5 is essential for the development of novel bile acid therapeutics targeting metabolic and neurodegenerative diseases. Herein, we describe the synthesis of 12β-methyl-18-nor-bile acids which may serve as probes in the search for new bile acid analogues with clinical applicability. A Nametkin-type rearrangement was applied to protected cholic acid derivatives, giving rise to tetra-substituted Δ13,14- and Δ13,17-unsaturated 12β-methyl-18-nor-bile acid intermediates (24a and 25a). Subsequent catalytic hydrogenation and deprotection yielded 12β-methyl-18-nor-chenodeoxycholic acid (27a) and its 17-epi-epimer (28a) as the two major reaction products. Optimization of the synthetic sequence enabled a chromatography-free route to prepare these bile acids at a multi-gram scale. In addition, the first cis-C-D ring-junctured bile acid and a new 14(13 → 12)-abeo-bile acid are described. Furthermore, deuteration experiments were performed to provide mechanistic insights into the formation of the formal anti-hydrogenation product 12β-methyl-18-nor-chenodeoxycholic acid (27a).

Total Synthesis of Enantiopure Chabrolonaphthoquinone B Via a Stereoselective Julia-Kocienski Olefination

The total synthesis of cytotoxic meroditerpenoid naphthoquinone derivative chabrolonaphthoquinone B (1) in an enantiospecific manner is divulged using a chiral pool approach. The key step of our synthetic route is a modified Julia olefination between a sulfone-bearing aliphatic fragment and a Diels-Alder-derived aromatic aldehyde, leading to the stereoselective construction of the E-trisubstituted double bond.

Analog synthesis of DAMASCENOLIDETM, an important aroma component of roses, and their odor properties

DAMASCENOLIDE^TM [1, 4-(4-methylpent-3-en-1-yl)furan-2(5H)-one], which has a citrus-like odor, is an important aroma component of roses. We have previously reported on the synthesis and odor evaluation of double-bond isomers of 1 and concluded that the position and the geometric isomerism of the double-bond had a significant effect on the odor. For the purpose of deepening knowledge about structure-odor relationships, we synthesized 13 analogs of compound 1 and evaluated their odors. As a result, it was found that the presence of two double-bonds and branched methyl group at the terminal position in the side chain was essential in order to have a citrus-like odor. Substitution of the side chain with appropriate length at the appropriate 4-position of the 2(5H)-furanone ring was also an important factor in determining the quality of the odor.

Basimarols A, B, and C, Highly Oxygenated Pimarane Diterpenoids from Basilicum polystachyon

The highly oxygenated pimarane diterpenoids basimarols A, B, and C (3-5) were isolated from the plant species Basilicum polystachyon, which was collected within the Australian arid zone. Structure elucidation was performed using a suite of spectroscopic techniques, including X-ray crystallography. Anticancer and anti-DENV activity of 3-5 was explored, but only limited activity was observed. More extensive antiviral evaluation of stachyonic acid A (1), which was also isolated from B. polystachyon, revealed broad spectrum antiviral activity against West Nile virus (Kunjin strain, WNV_Kun) and human influenza viruses H1N1 and H3N2.

Stachyonic Acid: A Dengue Virus Inhibitor from Basilicum polystachyon

Stachyonic acid A, arising from the first in-depth phytochemical investigation of the herb Basilicum polystachyon, was found to display potent inhibitory activity against dengue virus, with limited cytotoxicity. Andrographolide, a known dengue virus inhibitor and closely related labdane-type diterpene, is structurally more complex but displayed poor antiviral activity in the PRNT assay, and increased cytotoxicity in comparison. Furthermore, a Diels-Alder reaction with PTAD identified the active pharmacophore of stachyonic acid to be the conjugated diene.

Evaluation of the Anti-Trypanosomal Activity of Vietnamese Essential Oils, with Emphasis on Curcuma longa L. and Its Components

Human African trypanosomiasis (HAT), known as sleeping sickness and caused by Trypanosoma brucei, is threatening low-income populations in sub-Saharan African countries with 61 million people at risk of infection. In order to discover new natural products against HAT, thirty-seven Vietnamese essential oils (EOs) were screened for their activity in vitro on Trypanosoma brucei brucei (Tbb) and cytotoxicity on mammalian cells (WI38, J774). Based on the selectivity indices (SIs), the more active and selective EOs were analyzed by gas chromatography. The anti-trypanosomal activity and cytotoxicity of some major compounds (isolated or commercial) were also determined. Our results showed for the first time the selective anti-trypanosomal effect of four EOs, extracted from three Zingiberaceae species (Curcuma longa, Curcuma zedoaria, and Zingiber officinale) and one Lauraceae species (Litsea cubeba) with IC₅₀ values of 3.17 ± 0.72, 2.51 ± 1.08, 3.10 ± 0.08, and 2.67 ± 1.12 nL/mL respectively and SI > 10. Identified compounds accounted for more than 85% for each of them. Among the five major components of Curcuma longa EO, curlone is the most promising anti-trypanosomal candidate with an IC₅₀ of 1.38 ± 0.45 µg/mL and SIs of 31.7 and 18.2 compared to WI38 and J774 respectively.

Synthesis of Alkyl Citrates (-)-CJ-13,981, (-)-CJ-13,982, and (-)-L-731,120 via a Cyclobutene Diester

An efficient and step-economic new approach to alkyl citrate natural products from a cyclobutene diester is presented. The key sequence involves a formal [2 + 2]-cycloaddition of a silylketene acetal with dimethylacetylene dicarboxylate to provide the cyclobutene diester 14 with 4.5:1 stereoselectivity. Exposure of diester 14 in acidic methanol effected a hydrolysis, intramolecular oxy-Michael reaction, and cyclobutanone methanolysis cascade to give the triester 15. Iodination and elimination then afforded a key alkyl citrate alkene intermediate, which was converted into the natural products (-)-CJ-13,982 (1), (-)-CJ-13,981 (2), and (-)-L-731,120 (3) via a cross-metathesis and subsequent reduction.

Biomimetic Synthesis of Hyperjapones F-I

Hyperjapones F–I are tetracyclic meroterpenoids recently isolated from Hypericum japonicum. All four of these natural products have been synthesised using oxidative, intermolecular hetero-Diels–Alder reactions to couple their common biosynthetic precursor, norflavesone, to the appropriate monoterpene building blocks: sabinene, β-pinene, and α-pinene. The synthesis of enantiomerically pure hyperjapones H and I and comparison of their optical rotations to those of the natural samples indicated that these meroterpenoids are probably biosynthesised as either racemic or scalemic mixtures.

Total synthesis and structural elucidation of spongosoritin A

The total synthesis of two putative structures of spongosoritin A has established it's structure and absolute configuration as syn (6R,8R).

Inverting Steric Effects: Using "Attractive" Noncovalent Interactions To Direct Silver-Catalyzed Nitrene Transfer

Nitrene transfer (NT) reactions represent powerful and direct methods to convert C-H bonds into amine groups that are prevalent in many commodity chemicals and pharmaceuticals. The importance of the C-N bond has stimulated the development of numerous transition-metal complexes to effect chemo-, regio-, and diastereoselective NT. An ongoing challenge is to understand how subtle interactions between catalyst and substrate influence the site-selectivity of the C-H amination event. In this work, we explore the underlying reasons why Ag(tpa)OTf (tpa = tris(pyridylmethyl)amine) prefers to activate α-conjugated C-H bonds over 3° alkyl C(sp3)-H bonds and apply these insights to reaction optimization and catalyst design. Experimental results suggest possible roles of noncovalent interactions (NCIs) in directing the NT; computational studies support the involvement of π···π and Ag···π interactions between catalyst and substrate, primarily by lowering the energy of the directed transition state and reaction conformers. A simple Hess's law relationship can be employed to predict selectivities for new substrates containing competing NCIs. The insights presented herein are poised to inspire the design of other catalyst-controlled C-H functionalization reactions.

Stable isotope dilution assay (SIDA) and HS-SPME-GCMS quantification of key aroma volatiles for fruit and sap of Australian mango cultivars

Reported herein is a high throughput method to quantify in a single analysis the key volatiles that contribute to the aroma of commercially significant mango cultivars grown in Australia. The method constitutes stable isotope dilution analysis (SIDA) in conjunction with headspace (HS) solid-phase microextraction (SPME) coupled with gas-chromatography mass spectrometry (GCMS). Deuterium labelled analogues of the target analytes were either purchased commercially or synthesised for use as internal standards. Seven volatiles, hexanal, 3-carene, α-terpinene, p-cymene, limonene, α-terpinolene and ethyl octanoate, were targeted. The resulting calibration functions had determination coefficients (R²) ranging from 0.93775 to 0.99741. High recovery efficiencies for spiked mango samples were also achieved. The method was applied to identify the key aroma volatile compounds produced by 'Kensington Pride' and 'B74' mango fruit and by 'Honey Gold' mango sap. This method represents a marked improvement over current methods for detecting and measuring concentrations of mango fruit and sap volatiles.

Synthesis and Stereochemical Analysis of Planar-Chiral (E)-4-[7]Orthocyclophene

An efficient synthesis of (E)-4-[7]orthocyclophene (E)-1 via photochemical isomerization of (Z)-1 has been achieved. The key intermediate (Z)-1 was synthesized from commercially available 2-(hydroxymethyl)benzenepropanol (3) in five steps: (i) group-selective Mitsunobu reaction with CH₂═CHCH₂CH(SO₂Ph)₂, (ii) oxidation of alcohol, (iii) olefination, (iv) RCM, and (v) removal of sulfones in an overall yield of 73%. The photochemical isomerization of (Z)-1 was efficiently performed in the presence of AgNO₃-impregnated silica gel (AgNO₃/SiO₂). The resulting (E)-1 shows dynamic planar chirality at rt. Enantioenriched (E)-1 was prepared by the HPLC separation of enantiomers using a chiral stationary phase, and the absolute stereochemistry was determined by X-ray diffraction analysis of the Pt-coordinated crystalline derivative. The planar chirality of (E)-1 can be converted into the central chirality of carbon; e.g., the oxidation of (R)-(E)-1 using DMDO provided epoxide (8S,9S)-9 in a stereospecific manner. Furthermore, the Lewis acid-promoted reaction of (8S,9S)-9 afforded a unique tricyclic compound (8S,9S)-10 in an excellent yield and in a stereospecific manner.

Retention in Porous Layer Pillar Array Planar Separation Platforms

This work presents the retention capabilities and surface area enhancement of highly ordered, high-aspect-ratio, open-platform, two-dimensional (2D) pillar arrays when coated with a thin layer of porous silicon oxide (PSO). Photolithographically prepared pillar arrays were coated with 50-250 nm of PSO via plasma-enhanced chemical vapor deposition and then functionalized with either octadecyltrichlorosilane or n-butyldimethylchlorosilane. Theoretical calculations indicate that a 50 nm layer of PSO increases the surface area of a pillar nearly 120-fold. Retention capabilities were tested by observing capillary-action-driven development under various conditions, as well as by running one-dimensional separations on varying thicknesses of PSO. Increasing the thickness of PSO on an array clearly resulted in greater retention of the analyte(s) in question in both experiments. In culmination, a two-dimensional separation of fluorescently derivatized amines was performed to further demonstrate the capabilities of these fabricated platforms.

Biomimetic Total Synthesis of Hyperjapones A-E and Hyperjaponols A and C

Hyperjapones A-E and hyperjaponols A-C are complex natural products of mixed aromatic polyketide and terpene biosynthetic origin that have recently been isolated from Hypericum japonicum. We have synthesized hyperjapones A-E using a biomimetic, oxidative hetero-Diels-Alder reaction to couple together dearomatized acylphloroglucinol and cyclic terpene natural products. Hyperjapone A is proposed to be the biosynthetic precursor of hyperjaponol C through a sequence of: 1) epoxidation; 2) acid-catalyzed epoxide ring-opening; and 3) a concerted, asynchronous alkene cyclization and 1,2-alkyl shift of a tertiary carbocation. Chemical mimicry of this proposed biosynthetic sequence allowed a concise total synthesis of hyperjaponol C to be completed in which six carbon-carbon bonds, six stereocenters, and three rings were constructed in just four steps.

Palladium-Catalyzed 1,3-Difunctionalization Using Terminal Alkenes with Alkenyl Nonaflates and Aryl Boronic Acids

A Pd-catalyzed 1,3-difunctionalization of terminal alkenes using 1,1-disubstituted alkenyl nonaflates and arylboronic acid coupling partners is reported. This transformation affords allylic arene products that are difficult to selectively access using traditional Heck cross-coupling methodologies. The evaluation of seldom employed 1,1-disubstituted alkenyl nonaflate coupling partners led to the elucidation of subtle mechanistic features of π-allyl stabilized Pd-intermediates. Good stereo- and regioselectivity for the formation of 1,3-addition products can be accessed through a minimization of steric interactions that emanate from alkenyl nonaflate substitution.

Anesthetic activity and bio-guided fractionation of the essential oil of Aloysia gratissima (Gillies & Hook.) Tronc. in silver catfish Rhamdia quelen

This work aimed to determine the efficacy of the essential oil of A. gratissima as anesthetic for silver catfish, and to perform the bio-guided fractionation of essential oil aiming to isolate compounds responsible for the noted effects. Fish were submitted to anesthesia bath with essential oil, its fractions and isolated compounds to determine time of anesthetic induction and recovery. Eugenol (50 mg L(-1)) was used as positive control. Essential oil of A. gratissima was effective as an anesthetic at concentrations of 300 to 900 mg L(-1). Fish presented involuntary muscle contractions during induction and recovery. The bio-guided fractionation of essential oil furnished E-(-)-pinocamphone, (-)-caryophyllene oxide, (-)-guaiol and (+)-spathulenol. E-(-)-pinocamphone caused the same side effects observed for essential oil. (-)-Caryophyllene oxide, (-)-guaiol and (+)-spathulenol showed only sedative effects at proportional concentrations to those of the constituents in essential oil. (+)-Spathulenol (51.2 mg L(-1)) promoted deep anesthesia without side effects. A higher concentration of (+)-spathulenol, and lower or absent amounts ofE-(-)-pinocamphone could contribute to increase the activity and safety of the essential oil of A. gratissima. (+)-Spathulenol showed potent sedative and anesthetic activities in silver catfish, and could be considered as a viable compound for the development of a new anesthetic.

Enantiospecific intramolecular Heck reactions of secondary benzylic ethers

Enantioenriched methylenecyclopentanes are synthesized by stereospecific, nickel-catalyzed Heck cyclizations of secondary benzylic ethers. The reaction proceeds in high yield and enantiospecificity for benzylic ethers of both π-extended and simple arenes. Ethers with pendant 1,2-disubstituted olefins form trisubstituted olefins with control of both absolute configuration and alkene geometry. Diastereoselective synthesis of a polycyclic furan is demonstrated.