A chlorinated amide and piperidine alkaloids from Aloe sabaea

Mass Spectrometry Imaging of Coniine and Other Hemlock Alkaloids after On-Tissue Derivatization Reveals Distinct Alkaloid Distributions in the Plant

Specialized metabolites play important roles in plants and can, for example, protect plants from predators or pathogens. Alkaloids, due to their pronounced biological activity on higher animals, are one of the most intriguing groups of specialized metabolites, and many of them are known as plant defense compounds. Poison hemlock, Conium maculatum, is well-known for its high content of piperidine alkaloids, of which coniine is the most famous. The distribution, localization, and diversity of these compounds in C. maculatum tissues have not yet been studied in detail. The hemlock alkaloids are low molecular weight compounds with relatively high volatility. They are thus difficult to analyze on-tissue by MALDI mass spectrometry imaging due to delocalization, which occurs even when using an atmospheric pressure ion source. In this manuscript, we describe an on-tissue derivatization method that allows the subsequent determination of the spatial distribution of hemlock alkaloids in different plant tissues by mass spectrometry imaging. Coniferyl aldehyde was found to be a suitable reagent for derivatization of the secondary amine alkaloids. The imaging analysis revealed that even chemically closely related hemlock alkaloids are discretely distributed in different plant tissues. Additionally, we detected a yet undescribed hemlock alkaloid in Conium maculatum seeds.

Chemical structures, biological activities, and medicinal potentials of amine compounds detected from Aloe species

Unrestricted interest in Aloe species has grown rapidly, and a lot of research is currently being done to learn more about the properties of the various Aloe constituents. Organic compounds containing amine as functional group are present in a vivid variety of compounds, namely, amino acids, hormones, neurotransmitters, DNA, alkaloids, dyes, etc. These compounds have amine functional groups that have various biological activities, which make them responsible for medicinal potential in the form of pharmaceutical, nutraceutical, and cosmeceutical applications. Consequently, the present review work provides an indication of the amines investigated in Aloe species and their therapeutic uses. Various amine compounds of the Aloe species have effective biological properties to treat diseases. Generally, the genus Aloe has various active amine-containing compounds to combat diseases when humans use them in various forms.

Aloe adigratana Reynolds: Preliminary Phytochemical Screening, Proximate Content, Essential Oil Analysis, and In Vitro Antifungal Activity Studies of Its Leaf Peels and Gel

Background

Aloe species are among the most significant plants with several applications. Many of the species, however, are underexplored, owing to their scarcity and limited geographical distribution. A. adigratana Reynolds, which is common in Ethiopia, is one of the little-studied and endangered Aloe species.

Objective

This preliminary study focuses on the phytochemical screening, proximate analysis, essential oil content, and antifungal activities of A. adigratana leaf peels. Antifungal activities were also tested on the gels of the plant for comparison.

Methods

Standard procedures were used for phytochemical and proximate composition studies. Essential oil analysis was performed using a gas chromatography-mass spectrometry instrument. Using the well-diffusion method, investigations on antifungal activity were performed on three clinically isolated specimens of dandruff-causing fungus; namely, Malassezia furfur, Malassezia restricta, and Malassezia globosa.

Results

The leaf peels of A. adigratana contained alkaloids, flavonoids, tannins, and terpenes. The mean moisture, ash, and crude fat levels were 85.69, 92.20, and 8.00%, respectively, whereas the mean total protein and mean total carbohydrate values were 2.59 and 3.04%. Gas chromatography-mass spectrometry investigation confirmed the presence of fifteen essential oils. The most prevalent essential oil component was discovered to be phytol (33.78%), followed by decane (11.29%). In a dose-dependent way, the leaf latex and gel extracts prevented the growth of three dandruff-causing Malassezia fungal species (M. furfur, M. restricta, and M. globosa). Both the latex and gel demonstrated the maximum activity on M. globosa, the most prevalent fungus in the research area, with minimum inhibitory concentrations of 0.24 and 0.48 mg/mL and minimum fungicidal concentrations of 0.48 and 0.97 mg/mL, respectively.

Conclusion

In general, the proximate and essential oil compositions of A. adigratana leaves were comparable to those of other Aloe species widely used in the food, cosmetic, and pharmaceutical industries, implying that A. adigratana could be a potential future plant for such industries.

De novo transcriptome assembly of Conium maculatum L. to identify candidate genes for coniine biosynthesis

Poison hemlock (Conium maculatum L.) is a notorious weed containing the potent alkaloid coniine. Only some of the enzymes in the coniine biosynthesis have so far been characterized. Here, we utilize the next-generation RNA sequencing approach to report the first-ever transcriptome sequencing of five organs of poison hemlock: developing fruit, flower, root, leaf, and stem. Using a de novo assembly approach, we derived a transcriptome assembly containing 123,240 transcripts. The assembly is deemed high quality, representing over 88% of the near-universal ortholog genes of the Eudicots clade. Nearly 80% of the transcripts were functionally annotated using a combination of three approaches. The current study focuses on describing the coniine pathway by identifying in silico transcript candidates for polyketide reductase, L-alanine:5-keto-octanal aminotransferase, γ-coniceine reductase, and S-adenosyl-L-methionine:coniine methyltransferase. In vitro testing will be needed to confirm the assigned functions of the selected candidates.

Identification of Potential SARS-CoV-2 Main Protease and Spike Protein Inhibitors from the Genus Aloe: An In Silico Study for Drug Development

Severe acute respiratory syndrome coronavirus (SARS-CoV-2) disease is a global rapidly spreading virus showing very high rates of complications and mortality. Till now, there is no effective specific treatment for the disease. Aloe is a rich source of isolated phytoconstituents that have an enormous range of biological activities. Since there are no available experimental techniques to examine these compounds for antiviral activity against SARS-CoV-2, we employed an in silico approach involving molecular docking, dynamics simulation, and binding free energy calculation using SARS-CoV-2 essential proteins as main protease and spike protein to identify lead compounds from Aloe that may help in novel drug discovery. Results retrieved from docking and molecular dynamics simulation suggested a number of promising inhibitors from Aloe. Root mean square deviation (RMSD) and root mean square fluctuation (RMSF) calculations indicated that compounds 132, 134, and 159 were the best scoring compounds against main protease, while compounds 115, 120, and 131 were the best scoring ones against spike glycoprotein. Compounds 120 and 131 were able to achieve significant stability and binding free energies during molecular dynamics simulation. In addition, the highest scoring compounds were investigated for their pharmacokinetic properties and drug-likeness. The Aloe compounds are promising active phytoconstituents for drug development for SARS-CoV-2.

Investigation of Adsorption Effect of Carbon Monoxide on Coniine: A DFT Study

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For the first time in the present study, the non-bonded interaction of the Coniine (C8H17N) with carbon monoxide (CO) was investigated by density functional theory (DFT/M062X/6-311+G*) in the gas phase and solvent water. The adsorption of the CO over C8H17N was affected on the electronic properties such as EHOMO, ELUMO, the energy gap between LUMO and HOMO, global hardness. Furthermore, chemical shift tensors and natural charge of the C8H17N and complex C8H17N/CO were determined and discussed. According to the natural bond orbital (NBO) results, the molecule C8H17N and CO play as both electron donor and acceptor at the complex C8H17N/CO in the gas phase and solvent water. On the other hand, the charge transfer is occurred between the bonding, antibonding or nonbonding orbitals in two molecules C8H17N and CO. We have also investigated the charge distribution for the complex C8H17N/CO by molecular electrostatic potential (MEP) calculations using the M062X/6-311+G* level of theory. The electronic spectra of the C8H17N and complex C8H17N/CO were calculated by time dependent DFT (TD-DFT) for investigation of the maximum wavelength value of the C8H17N before and after the non-bonded interaction with the CO in the gas phase and solvent water. Therefore, C8H17N can be used as strong absorbers for air purification and reduce environmental pollution.

Bacterial Analogs of Plant Tetrahydropyridine Alkaloids Mediate Microbial Interactions in a Rhizosphere Model System

The microbiomes of plants are critical to host physiology and development. Microbes are attracted to the rhizosphere due to massive secretion of plant photosynthates from roots. Microorganisms that successfully join the rhizosphere community from bulk soil have access to more abundant and diverse molecules, producing a highly competitive and selective environment. In the rhizosphere, as in other microbiomes, little is known about the genetic basis for individual species’ behaviors within the community. In this study, we characterized competition between Pseudomonas koreensis and Flavobacterium johnsoniae, two common rhizosphere inhabitants. We identified a widespread gene cluster in several Pseudomonas spp. that is necessary for the production of a novel family of tetrahydropyridine alkaloids that are structural analogs of plant alkaloids. We expand the known repertoire of antibiotics produced by Pseudomonas in the rhizosphere and demonstrate the role of the metabolites in interactions with other rhizosphere bacteria.

Plants expend significant resources to select and maintain rhizosphere communities that benefit their growth and protect them from pathogens. A better understanding of assembly and function of rhizosphere microbial communities will provide new avenues for improving crop production. Secretion of antibiotics is one means by which bacteria interact with neighboring microbes and sometimes change community composition. In our analysis of a taxonomically diverse consortium from the soybean rhizosphere, we found that Pseudomonas koreensis selectively inhibits growth of Flavobacterium johnsoniae and other members of the Bacteroidetes grown in soybean root exudate. A genetic screen in P. koreensis identified a previously uncharacterized biosynthetic gene cluster responsible for the inhibitory activity. Metabolites were isolated based on biological activity and were characterized using tandem mass spectrometry, multidimensional nuclear magnetic resonance, and Mosher ester analysis, leading to the discovery of a new family of bacterial tetrahydropyridine alkaloids, koreenceine A to D (metabolites 1 to 4). Three of these metabolites are analogs of the plant alkaloid γ-coniceine. Comparative analysis of the koreenceine cluster with the γ-coniceine pathway revealed distinct polyketide synthase routes to the defining tetrahydropyridine scaffold, suggesting convergent evolution. Koreenceine-type pathways are widely distributed among Pseudomonas species, and koreenceine C was detected in another Pseudomonas species from a distantly related cluster. This work suggests that Pseudomonas and plants convergently evolved the ability to produce similar alkaloid metabolites that can mediate interbacterial competition in the rhizosphere.

IMPORTANCE The microbiomes of plants are critical to host physiology and development. Microbes are attracted to the rhizosphere due to massive secretion of plant photosynthates from roots. Microorganisms that successfully join the rhizosphere community from bulk soil have access to more abundant and diverse molecules, producing a highly competitive and selective environment. In the rhizosphere, as in other microbiomes, little is known about the genetic basis for individual species’ behaviors within the community. In this study, we characterized competition between Pseudomonas koreensis and Flavobacterium johnsoniae, two common rhizosphere inhabitants. We identified a widespread gene cluster in several Pseudomonas spp. that is necessary for the production of a novel family of tetrahydropyridine alkaloids that are structural analogs of plant alkaloids. We expand the known repertoire of antibiotics produced by Pseudomonas in the rhizosphere and demonstrate the role of the metabolites in interactions with other rhizosphere bacteria.

Aloe Genus Plants: From Farm to Food Applications and Phytopharmacotherapy

Aloe genus plants, distributed in Old World, are widely known and have been used for centuries as topical and oral therapeutic agents due to their health, beauty, medicinal, and skin care properties. Among the well-investigated Aloe species are A. arborescens, A. barbadensis, A. ferox, and A. vera. Today, they account among the most economically important medicinal plants and are commonly used in primary health treatment, where they play a pivotal role in the treatment of various types of diseases via the modulation of biochemical and molecular pathways, besides being a rich source of valuable phytochemicals. In the present review, we summarized the recent advances in botany, phytochemical composition, ethnobotanical uses, food preservation, and the preclinical and clinical efficacy of Aloe plants. These data will be helpful to provide future directions for the industrial and medicinal use of Aloe plants.

The killer of Socrates: Coniine and Related Alkaloids in the Plant Kingdom

Coniine, a polyketide-derived alkaloid, is poisonous to humans and animals. It is a nicotinic acetylcholine receptor antagonist, which leads to inhibition of the nervous system, eventually causing death by suffocation in mammals. Coniine’s most famous victim is Socrates who was sentenced to death by poison chalice containing poison hemlock in 399 BC. In chemistry, coniine holds two historical records: It is the first alkaloid the chemical structure of which was established (in 1881), and that was chemically synthesized (in 1886). In plants, coniine and twelve closely related alkaloids are known from poison hemlock (Conium maculatum L.), and several Sarracenia and Aloe species. Recent work confirmed its biosynthetic polyketide origin. Biosynthesis commences by carbon backbone formation from butyryl-CoA and two malonyl-CoA building blocks catalyzed by polyketide synthase. A transamination reaction incorporates nitrogen from l-alanine and non-enzymatic cyclization leads to γ-coniceine, the first hemlock alkaloid in the pathway. Ultimately, reduction of γ-coniceine to coniine is facilitated by NADPH-dependent γ-coniceine reductase. Although coniine is notorious for its toxicity, there is no consensus on its ecological roles, especially in the carnivorous pitcher plants where it occurs. Lately there has been renewed interest in coniine’s medical uses particularly for pain relief without an addictive side effect.

Therapeutic effects of Aloe spp. in traditional and modern medicine: A review

Traditional medicine is a useful guide in medical sciences. In the Islamic Iranian traditional medicine, the medicinal properties of many plants have been mentioned that could be exploited in drug discovery. We aimed to explore the nature and properties of Aloe spp. As described in some major Islamic traditional texts including Ferdows al-Hekmah fi'l-Tibbe (The Paradise of Wisdom in Medicine), Al-Hawi fi'l-Tibb (Comprehensive Book of Medicine), Kamel al-Sanaat al-Tibbyyah (Complete Book of the Medical Art), Al-Qanun fi'l-Tibb (Canon of Medicine), Zakhireh Kharazmshahi (Treasure of Kharazmshah), and Makhzan al-Adwiah (Drug Treasure), and assess the conformity of traditional medicine instructions with the findings of modern pharmacological studies. Gastrointestinal activities, hepato-protective properties, beneficial effects against skin problems such as wounds, injuries, and infective diseases are among the most frequently mentioned properties of Aloe spp. Several activities of Aloe spp. described in traditional medicine have been the subject of recent in vitro and in vivo studies as well as clinical trials. Owing to the positive findings, different preparations of Aloe spp. are now present in pharmaceutical markets such as Aloe cosmetic products. On the other hand, there are many traditional therapeutic effects of Aloe spp. which have not been studied and require confirmatory experimental or clinical investigations. It is hoped that the present study could stimulate further research on the unexplored aspects of the medicinal properties of Aloe spp.

Isolation of antiplasmodial anthraquinones from Kniphofia ensifolia, and synthesis and structure-activity relationships of related compounds

Bioassay-guided separation of the South African plant Kniphofia ensifolia for antiplasmodial activity led to the isolation of two new anthraquinones, named kniphofiones A and B (3 and 4), together with three known bioactive anthraquinone monomers (1, 2 and 5), and four known bisanthraquinones (6-9). The structures of the two new compounds were elucidated based on analyses of their 1D and 2D NMR spectra and mass spectrometric data. The dimeric compounds 6 and 7 displayed the strongest antiplasmodial activity among all the isolated compounds, with IC₅₀ values of 0.4 ± 0.1 and 0.2 ± 0.1 μM, respectively. The two new compounds displayed modest activities, with IC₅₀ values of 26 ± 4 and 9 ± 1 μM, respectively. Due to the synthetic accessibility of the new compounds and the increased activity shown by the dimeric compounds, a structure-activity relationship study was conducted. As a result, one analogue of kniphofione B (4), the caffeic acid derivative of aloe-emodin, was found to have the highest activity among all the aloe-emodin derivatives, with an IC50 value of 1.3 ± 0.2 μM.

Piperidine alkaloids: human and food animal teratogens

Piperidine alkaloids are acutely toxic to adult livestock species and produce musculoskeletal deformities in neonatal animals. These teratogenic effects include multiple congenital contracture (MCC) deformities and cleft palate in cattle, pigs, sheep, and goats. Poisonous plants containing teratogenic piperidine alkaloids include poison hemlock (Conium maculatum), lupine (Lupinus spp.), and tobacco (Nicotiana tabacum) [including wild tree tobacco (Nicotiana glauca)]. There is abundant epidemiological evidence in humans that link maternal tobacco use with a high incidence of oral clefting in newborns; this association may be partly attributable to the presence of piperidine alkaloids in tobacco products. In this review, we summarize the evidence for piperidine alkaloids that act as teratogens in livestock, piperidine alkaloid structure-activity relationships and their potential implications for human health.

Hemlock alkaloids from Socrates to poison aloes

Hemlock (Conium maculatum L. Umbelliferae) has long been known as a poisonous plant. Toxicity is due to a group of piperidine alkaloids of which the representative members are coniine and gamma-coniceine. The latter is the more toxic and is the first formed biosynthetically. Its levels in relation to coniine vary widely according to environmental conditions and to provenance of the plants. Surprisingly, these piperidine alkaloids have turned up in quite unrelated species in the monocotyledons as well as the dicotyledons. Aloes, for instance, important medicinal plants, are not regarded as poisonous although some species are very bitter. Nevertheless a small number of mostly local species contain the alkaloids, especially gamma-coniceine and there have been records of human poisoning. The compounds are recognized by their characteristic mousy smell. Both acute and chronic symptoms have been described. The compounds are neurotoxins and death results from respiratory failure, recalling the effects of curare. Chronic non-lethal ingestion by pregnant livestock leads to foetal malformation. Both acute and chronic toxicity are seen with stock in damp meadows and have been recorded as problems especially in North America. The alkaloids derive biosynthetically from acetate units via the polyketide pathway in contrast to other piperidine alkaloids which derive from lysine.

Natural halogenated fatty acids: their analogues and derivatives

A comprehensive survey has been made of all fatty acids containing halogen atoms covalently bonded to carbon and which are deemed as naturally occurring. Generally thought to be minor components produced by many different organisms, these interesting compounds now number more than 300. Recent research, especially in the marine area, indicates this number will increase in the future. Sources of halogenated fatty acids include microorganisms, algae, marine invertebrates, and higher plants and some animals. Their possible biological significance has also been discussed