Cannabis through the looking glass: chemo- and enantio-selective separation of phytocannabinoids by enantioselective ultra high performance supercritical fluid chromatography

Analysis of phytocannabinoids in hemp seeds, sprouts and microgreens

Hemp-sprouts are emerging as a new class of attractive functional food due to their numerous health benefits when compared to other sprout species. Indeed, the high content of beneficial components including polyphenols and flavonoids makes this type of food a promising and successful market. However, the available literature on this topic is limited and often conflicting as regards to the content of phytocannabinoids. High-performance liquid chromatography coupled to high-resolution mass spectrometry (HPLC-HRMS) was applied in an untargeted metabolomics fashion to extracts of hemp seeds, sprouts and microgreens of nine different genotypes. Both unsupervised and supervised multivariate statistical analysis was performed to reveal variety-specific profiles of phytocannabinoids with surprisingly remarkable levels of phytocannabinoids even in chemotype V samples. Furthermore, a targeted HPLC-HRMS analysis was carried out for the quantitative determination of the major phytocannabinoids including CBDA, CBD, CBGA, CBG, CBCA, CBC, THCA, and trans-Δ9-THC. The last part of the study was focused on the evaluation of the enantiomeric composition of CBCA in hemp seeds, sprouts and microgreens in the different varieties by HPLC-CD (HPLC with online circular dichroism). Chiral analysis of CBCA showed a wide variability of its enantiomeric composition in the different varieties, thus contributing to the understanding of the intriguing stereochemical behavior of this compound in an early growth stage. However, further investigation is needed to determine the genetic factors responsible for the low enantiopurity of this compound.

A Simple Chiral 1H NMR Method for the Discrimination of (R)- and (S)-Cannabichromene in Complex Natural Mixtures and Their Effects on TRPA1 Activity

In recent years, the enantiomeric ratio of cannabichromene (CBC) within the cannabis plant has attracted significant attention. Cannabichromene is one of the well-known cannabinoids found in cannabis, along with THC (tetrahydrocannabinol) and CBD (cannabidiol). Cannabichromene exists as a scalemic mixture, meaning it has two enantiomers, (S)-cannabichromene and (R)-cannabichromene, with the ratio between these enantiomers varying among different cannabis strains and even within individual plants. This study presents an accurate and robust chiral NMR method for analyzing cannabichromene's enantiomeric ratio, a well-investigated cannabinoid with numerous pharmacological targets. The use of Pirkle's alcohol as the chiral solvating agent (CSA) or, alternatively, the use of (S)-ibuprofen as a chiral derivatizing agent (CDA) facilitated this analysis. Moreover, the chiral NMR method proves to be a user-friendly tool, easily applicable within any NMR facility, and an expanded investigation of cannabichromene chirality may provide insights into the origin, cultivation, treatment, and processing of Cannabis sativa plants. This study also undertakes a pharmacological examination of the (R)- and (S)-cannabichromenes concerning their most extensively studied pharmacological target, the TRPA1 channels, with the two enantiomers showing the same strong agonistic effect as the racemic mixture.

Recent developments in the high-throughput separation of biologically active chiral compounds via high performance liquid chromatography

Bioactive compounds, including active pharmaceutical ingredients (APIs), are often chiral molecules where stereoisomers have different biological and therapeutic activity. Nevertheless, the preparation of these molecules can lead to racemic or scalemic mixtures (it is not trivial to produce just the optically pure compound). The evaluation of the enantiomeric purity of bioactive compounds, and therefore quality, is indeed of fundamental importance for regulatory scopes. Chiral high performance liquid chromatography (HPLC) is the gold standard technique to separate and to purify enantiomers. This comes from the wide availability of commercial chiral stationary phases (CSPs) and operational modes, which makes the technique extremely versatile. In recent years, the most relevant trend in the field of chiral analytical HPLC has been the development of CSPs suitable for fast or even ultrafast separations, thus favoring the high throughput screening of biologically active chiral compounds. This process has somehow lagged behind compared to achiral HPLC, due to a series of practical and fundamental issues. The experience has shown how in chiral chromatography even very basic concepts, such as the supposed kinetic superiority of core-shell (pellicular) particles over fully porous ones to improve the chromatographic efficiency, cannot be taken for granted. In this review, the most relevant fundamental and practical features that must be taken into consideration to design successful high-throughput, fast enantioseparations will be discussed. Afterwards, the main classes of CSPs and the most relevant, recent (last five-year) high-throughput applications in the field of the separation of chiral bioactive compounds (for pharmaceutical, forensic, food, and omics applications) will be considered.

Bidimensional heart-cut achiral-chiral liquid chromatography coupled to high-resolution mass spectrometry for the separation of the main chiral phytocannabinoids and enantiomerization studies of cannabichromene and cannabichromenic acid

In this work, a heart-cut bidimensional achiral-chiral liquid chromatography method coupled to high-resolution mass spectrometry was developed for the separation of the main carboxylated phytocannabinoids, namely cannabidiolic acid (CBDA), tetrahydrocannabinolic acid (THCA), cannabichromenic acid (CBCA), and cannabicyclolic acid (CBLA), and decarboxylated derivatives, namely cannabidiol (CBD), Δ9-tetrahydrocannabinol (Δ9-THC), cannabichromene (CBC), and cannabicyclol (CBL), and the evaluation of their enantiomeric composition in extracts of different Cannabis sativa L. varieties. Optimal conditions for the chiral analysis of CBC- and CBL-type compounds were found with methanol and water (95:5, v/v, with 0.1% formic acid, 1.5 mL/min) on an amylose-based chiral stationary phase. These settings also allowed to evaluate the parameters responsible for CBC and CBCA racemization.

Scalemic natural products

Covering: up to the end of 2022The area of scalemic natural products is often enigmatic from a mechanistic standpoint, since low optical purity is observed in compounds having multiple contiguous stereogenic centers resulting from mechanistically distinct biogenetic steps. A scalemic state is rarely the result of a sloppy enzymatic activity, rather resulting from the expression of antipodal enzymes/directing proteins or from the erosion of optical purity by enzymatic or spontaneous reactions. Evidence for these processes is critically reviewed, identifying the mechanisms most often associated to the enzymatic generation of scalemic natural products and also discussing analytical exploitations of natural products' scalemicity.

Natural Cannabichromene (CBC) Shows Distinct Scalemicity Grades and Enantiomeric Dominance in Cannabis sativa Strains

Cannabichromene (CBC, 1a) occurs in Cannabis (Cannabis sativa) as a scalemate having a composition that is strain-dependent in terms of both enantiomeric excess and enantiomeric dominance. In the present work, the chirality of CBC (1a), a noncrystalline compound, was shown not to be significantly affected by standard conditions of isolation and purification, and enantiomeric self-disproportionation effects were minimized by carrying out the chiral analysis on crude fractions rather than on purified products. A genetic basis for the different enantiomeric state of CBC in Cannabis therefore seems to exist, implying that the chirality status of natural CBC (1a) in the plant is associated with the differential expression of CBCA-synthase isoforms and/or of associated directing proteins with antipodal enantiospecificity. The biological profile of both enantiomers of CBC should therefore be investigated independently to assess the contribution of this compound to the activity of Cannabis preparations.

Enantioseparation of chiral phytocannabinoids in medicinal cannabis

The evaluation of the chiral composition of phytocannabinoids in the cannabis plant is particularly important as the pharmacological effects of the (+) and (-) enantiomers of these compounds are completely different. Chromatographic attempts to assess the presence of the minor (+) enantiomers of the main phytocannabinoids, cannabidiolic acid (CBDA) and trans-Δ⁹-tetrahydrocannabinolic acid (trans-Δ⁹-THCA), were carried out on heated plant extracts for the determination of the corresponding decarboxylated species, cannabidiol (CBD) and trans-Δ⁹-tetrahydrocannabinol (trans-Δ⁹-THC), respectively. This process produces an altered phytocannabinoid composition with several new and unknown decomposition products. The present work reports for the first time the stereoselective synthesis of the pure (+) enantiomers of the main phytocannabinoids, trans-CBDA, trans-Δ⁹-THCA, trans-CBD and trans-Δ⁹-THC, and the development and optimization of an achiral-chiral liquid chromatography method coupled to UV and high-resolution mass spectrometry detection in reversed phase conditions (RP-HPLC-UV-HRMS) for the isolation of the single compounds and evaluation of their actual enantiomeric composition in plant. The isolation of the peaks with the achiral stationary phase ensured the absence of interferences that could potentially co-elute with the analytes of interest in the chiral analysis. The method applied to the Italian medicinal cannabis variety FM2 revealed no trace of the (+) enantiomers for all phytocannabinoids under investigation before and after decarboxylation, thus suggesting that the extraction procedure does not lead to an inversion of configuration.

Chiral Separation of Cannabichromene, Cannabicyclol, and Their Acidic Analogs on Polysaccharide Chiral Stationary Phases

Until recently, chirality has not been a major focus in the study of cannabinoids, as most cannabinoids of interest, such as cannabidiol and tetrahydrocannabinol, exist as a single isomer from natural sources. However, this is changing as more cannabinoids are identified, and compounds such as cannabichromene and cannabicyclol are emerging as potential investigatory candidates for varying indications. Because these molecules are chiral, the separation and study of the individual enantiomers' biological and physiological effects should therefore be of interest. The purpose of this study was to identify analytical separation conditions and then adapt those conditions to preparative separation. This was accomplished with a column-screening approach on Daicel's immobilized polysaccharide chiral stationary phases using non-traditional mobile phases, which included dichloromethane, ethyl acetate, and methyl tert-butyl ether under high-performance liquid chromatography conditions. CHIRALPAK^® IK was found to separate all four compounds well with mobile phases containing hexane-dichloromethane (with or without an acidic additive). From these methods, the separation productivities were calculated to better visualize the separation scalability, which shows that the kilogram-scale separations of each are feasible.

Biosynthetic origins of unusual cannabimimetic phytocannabinoids in Cannabis sativa L: A review

Plants of Cannabis sativa L. (Cannabaceae) produce an array of more than 160 isoprenylated resorcinyl polyketides, commonly referred to as phytocannabinoids. These compounds represent molecules of therapeutic importance due to their modulation of the human endocannabinoid system (ECS). While understanding of the biosynthesis of the major phytocannabinoids Δ⁹-tetrahydrocannabinol (Δ⁹-THC) and cannabidiol (CBD) has grown rapidly in recent years, the biosynthetic origin and genetic regulation of many potentially therapeutically relevant minor phytocannabinoids remain unknown, which limits the development of chemotypically elite varieties of C. sativa. This review provides an up-to-date inventory of unusual phytocannabinoids which exhibit cannabimimetic-like activities and proposes putative metabolic origins. Metabolic branch points exploitable for combinatorial biosynthesis and engineering of phytocannabinoids with augmented therapeutic activities are also described, as is the role of phytocannabinoid remodelling to accelerate the therapeutic portfolio expansion in C. sativa.

Minor Phytocannabinoids: A Misleading Name but a Promising Opportunity for Biomedical Research

Despite the very large number of phytocannabinoids isolated from Cannabis (Cannabis sativa L.), bioactivity studies have long remained focused on the so called “Big Four” [Δ⁹-THC (1), CBD (2), CBG (3) and CBC (4)] because of their earlier characterization and relatively easy availability via isolation and/or synthesis. Bioactivity information on the chemical space associated with the remaining part of the cannabinome, a set of ca 150 compounds traditionally referred to as “minor phytocannabinoids”, is scarce and patchy, yet promising in terms of pharmacological potential. According to their advancement stage, we sorted the bioactivity data available on these compounds, better referred to as the “dark cannabinome”, into categories: discovery (in vitro phenotypical and biochemical assays), preclinical (animal models), and clinical. Strategies to overcome the availability issues associated with minor phytocannabinoids are discussed, as well as the still unmet challenges facing their development as mainstream drugs.

Advanced Development of Supercritical Fluid Chromatography in Herbal Medicine Analysis

The greatest challenge in the analysis of herbal components lies in their variety and complexity. Therefore, efficient analytical tools for the separation and qualitative and quantitative analysis of multi-components are essential. In recent years, various emerging analytical techniques have offered significant support for complicated component analysis, with breakthroughs in selectivity, sensitivity, and rapid analysis. Among these techniques, supercritical fluid chromatography (SFC) has attracted much attention because of its high column efficiency and environmental protection. SFC can be used to analyze a wide range of compounds, including non-polar and polar compounds, making it a prominent analytical platform. The applicability of SFC for the separation and determination of natural products in herbal medicines is overviewed in this article. The range of applications was expanded through the selection and optimization of stationary phases and mobile phases. We also focus on the two-dimensional SFC analysis. This paper provides new insight into SFC method development for herbal medicine analysis.

Boosting the enantioresolution of zwitterionic-teicoplanin chiral stationary phases by moving to wide-pore core-shell particles

A novel zwitterionic-teicoplanin chiral stationary phase (CSP), based on superficially porous particles (SPPs) of 2.7 µm particle diameter and 160 Å pore size, has been prepared and evaluated towards the enantioseparation of important classes of compounds, including chiral drugs, pesticides, and N-derivatized amino acids. The comparison with two analogous CSPs prepared on SPPs with 2.7 and 2.0 µm particle diameter and 90 Å pore size has revealed that the use of large-pore particles allows to dramatically improve both the enantioselectivity and the resolution-per-analysis-time, at the point that the column prepared with the new CSP outperformed the one packed with the finest particles. On the novel wide-pore CSP, the separation of fifteen racemates of pratical importance was significantly improved in terms of both enantioselectivity and resolution-per-analysis time-compared to the CSPs based on SPPs with smaller pores (90 Å). Such a CSP would be suitable for very fast enantioseparations allowing the saving of solvent for greener high-efficiency/high-throughput applications.

Cannabidiol (CBD) From Non-Cannabis Plants: Myth or Reality?

Reports on the occurrence of cannabidiol (CBD, 1) in non-cannabis plants are critically reviewed. The isolation of 1 from Humulus Kriya (sic) was fraudulent and from Trema orientalis and stevia dubious, while the occurrence of traces of 1 in flax needs additional confirmation. The presence of high concentration of cannabigerol (CBG, 3a) and its corresponding acidic precursor (GBGA, 3b) in Helichrysum umbraculigerum could not be confirmed, but this plant deserves additional attention due to the possible phytocannabinoids accumulation in selected chemotypes.

A Nrf-2 Stimulatory Hydroxylated Cannabidiol Derivative from Hemp (Cannabis sativa)

A phytochemical analysis of mother liquors obtained from crystallization of CBD from hemp (Cannabis sativa), guided by LC-MS/MS and molecular networking profiling and completed by isolation and NMR-based characterization of constituents, resulted in the identification of 13 phytocannabinoids. Among them, anhydrocannabimovone (5), isolated for the first time as a natural product, and three new hydroxylated CBD analogues (1,2-dihydroxycannabidiol, 6, 3,4-dehydro-1,2-dihydroxycannabidiol, 7, and hexocannabitriol, 8) were obtained. Hexocannabitriol (8) potently modulated, in a ROS-independent way, the Nrf2 pathway, outperforming all other cannabinoids obtained in this study and qualifying as a potential new chemopreventive chemotype against cancer and other degenerative diseases.

Perspectives and Pitfalls in Potency Testing of Cannabinoids by High Performance Liquid Chromatography (HPLC)

Cannabis products have been recently legalized in many countries for recreational or medicinal use. Therefore, rigorous analytical methods to test the potency of samples is required prior to commercialization. In addition, growing interest in the properties of minor cannabinoids has increased the demand for high-throughput methods that can separate the largest number of compounds in the shortest amount of time. High performance liquid chromatography (HPLC) is emerging as the preferred analytical method for potency testing of cannabinoids, but more fundamental work is needed to solve critical issues and contribute to advancing knowledge.

The Separation of Cannabinoids on Sub-2 µm Immobilized Polysaccharide Chiral Stationary Phases

The increased use and applicability of Cannabis and Cannabis-derived products has skyrocketed over the last 5 years. With more and more governing bodies moving toward medical and recreational legalization, the need for robust and reliable analytical testing methods is also growing. While many stationary phases and methods have been developed for this sort of analysis, chiral stationary phases (CSPs) are unique in this area; not only can they serve their traditional chiral separation role, but they can also be used to perform achiral separations. Given that mixtures of cannabinoids routinely contain enantiomers, diastereomers, and structural isomers, this offers an advantage over the strictly achiral-only analyses. This work presents the separation of a 10-cannabinoid mixture on several polysaccharide-based sub-2 µm CSPs with both normal-phase and reversed-phase ultra-high-performance liquid chromatography (UHPLC) conditions. Along with the separation of the mixture, appropriate single-peak identification was performed to determine the elution order and reported where applicable.

Δ9-cis-Tetrahydrocannabinol: Natural Occurrence, Chirality, and Pharmacology

The cis-stereoisomers of Δ⁹-THC [(-)-3 and (+)-3] were identified and quantified in a series of low-THC-containing varieties of Cannabis sativa registered in Europe as fiber hemp and in research accessions of cannabis. While Δ⁹-cis-THC (3) occurs in cannabis fiber hemp in the concentration range of (-)-Δ⁹-trans-THC [(-)-1], it was undetectable in a sample of high-THC-containing medicinal cannabis. Natural Δ⁹-cis-THC (3) is scalemic (ca. 80-90% enantiomeric purity), and the absolute configuration of the major enantiomer was established as 6aS,10aR [(-)-3] by chiral chromatographic comparison with a sample available by asymmetric synthesis. The major enantiomer, (-)-Δ⁹-cis-THC [(-)-3], was characterized as a partial cannabinoid agonist in vitro and elicited a full tetrad response in mice at 50 mg/kg doses. The current legal discrimination between narcotic and non-narcotic cannabis varieties centers on the contents of "Δ⁹-THC and isomers" and needs therefore revision, or at least a more specific wording, to account for the presence of Δ⁹-cis-THCs [(+)-3 and (-)-3] in cannabis fiber hemp varieties.

Cannabichromene Racemization and Absolute Stereochemistry Based on a Cannabicyclol Analog

Cannabichromene (CBC) is unusual among cannabinoids in having been described as both a racemic and a scalemic compound from natural Cannabis sources. Several explanations are available for this circumstance, including facile racemization. Cannabichromene was resolved chromatographically, and the enantiomer matching CBC from local Cannabis was identified. To preclude racemization, CBC was converted to cannabicyclol for further stereochemical analysis. This permitted the (R) absolute stereochemistry to be assigned to natural CBC based on chiroptical data for related natural products and the absolute configuration of a cannabicyclol analog determined by X-ray crystallography. The racemization of CBC was found to be rather slow in the laboratory, but handling practices for natural cannabis products can be inferred to promote the process.

Potency testing of cannabinoids by liquid and supercritical fluid chromatography: Where we are, what we need

Hemp and cannabis industry is undergoing a renewed interest due to legalization of marijuana (a topic that all countries are discussing, especially in recent years) and the growing importance of therapeutic properties of cannabinoids. Together with an increment in the production of hemp and recreational cannabis, there has been an increasing demand for accurate potency testing of products (i.e. quantification of main cannabinoids present in the plant in terms of weight percentage) prior commercialization. This translates in an urgent need of reliable analytical methods to characterize cannabis and hemp samples. Cannabis and hemp preparations are commercialized under various forms (e.g., flowers, oils, candies or even baked goods) usually containing a large number of often very similar compounds making their separation very challenging. Strictly connected to this, another emerging topic concerns the need for the developing of large scale separation techniques for the purification of cannabinoids from complex matrices and for the preparation of analytical-grade standards (including the chiral ones). This paper reviews the most recent achievements in both these aspects. Cutting-edge applications and novel opportunities in potency testing by high performance liquid chromatography (HPLC) with UV detection (which is becoming the golden standard, according to several pharmacopeias, for this kind of measurements) are discussed. The focus has been given to the very important topic of enantio-discrimination of chiral cannabinoids, for which supercritical fluid chromatography (SFC) appears to be particularly suitable. The last part of the work covers the purification of cannabinoids through preparative chromatography. In this regard, particular attention has been given to the most innovative multi-column techniques allowing for the continuous purification of target molecules. The most recent advancements and future challenges in this field are discussed.

A Multimethodological Characterization of Cannabis sativa L. Inflorescences from Seven Dioecious Cultivars Grown in Italy: The Effect of Different Harvesting Stages

The chemical profile of the female inflorescence extracts from seven Cannabis sativa L. dioecious cultivars (Carmagnola, Fibranova, Eletta Campana, Antal, Tiborszallasi, Kompolti, and Tisza) was monitored at three harvesting stages (4, 14, and 30 September), reaching from the beginning of flowering to end of flowering/beginning of seed formation, using untargeted nuclear magnetic resonance (NMR) and targeted (ultra-high-performance liquid chromatography (UHPLC) and spectrophotometry) analyses. The tetrahydrocannabinol content was always below the legal limits (<0.6%) in all the analyzed samples. The NMR metabolite profile (sugars, organic acids, amino acids, and minor compounds) subjected to principal components analysis (PCA) showed a strong variability according to the harvesting stages: samples harvested in stage I were characterized by a high content of sucrose and myo-inositol, whereas the ones harvested in stage II showed high levels of succinic acid, alanine, valine, isoleucine, phenylalanine, and threonine. Samples harvested in stage III were characterized by high levels of glucose, fructose, choline, trigonelline, malic acid, formic acid, and some amino acids. The ratio between chlorophylls and carotenoids content indicated that all plants grew up exposed to the sun, the Eletta Campana cultivar having the highest pigment amount. Tiborszallasi cultivar showed the highest polyphenol content. The highest antioxidant activity was generally observed in stage II. All these results suggested that the Cannabis sativa L. inflorescences of each analyzed dioecious hemp cultivar presented a peculiar chemical profile affected by the harvesting stage. This information could be useful for producers and industries to harvest inflorescences in the appropriate stage to obtain samples with a peculiar chemical profile suitable for proper applications.

Using (+)-Carvone to access novel derivatives of (+)-ent-Cannabidiol: the first asymmetric syntheses of (+)-ent-CBDP and (+)-ent-CBDV

(-)-Cannabidiol [(-)-CBD] has recently gained prominence as a treatment for neuro-inflammation and other neurodegenerative disorders; interest is also developing in its synthetic enantiomer, (+)-CBD, which has a higher affinity to CB1 / CB2 receptors than the natural stereoisomer. We have developed an inexpensive, stereoselective route to access ent-CBD derivatives using (+)-carvone as a starting material. In addition to (+)-CBD, we report the first syntheses of (+)-cannabidivarin, (+)-cannabidiphorol as well as C-6 / C-8 homologues.

Chirality in Cannabinoid Research

Mankind has long utilized Cannabis for diverse purposes. However, it has only been since the late 19th century that its individual cannabinoids began to be isolated, analyzed, and synthesized. By the mid-20th century it was discovered that many cannabinoids were asymmetric, with chirality often controlling their pharmacology. Increasingly accurate measurement and understanding of cannabinoid chirality will facilitate their synthesis and accelerate their medicinal applications.

Phytocannabinoid Pharmacology: Medicinal Properties of Cannabis sativa Constituents Aside from the "Big Two"

Plant-based therapies date back centuries. Cannabis sativa is one such plant that was used medicinally up until the early part of the 20th century. Although rich in diverse and interesting phytochemicals, cannabis was largely ignored by the modern scientific community due to its designation as a schedule 1 narcotic and restrictions on access for research purposes. There was renewed interest in the early 1990s when the endocannabinoid system (ECS) was discovered, a complex network of signaling pathways responsible for physiological homeostasis. Two key components of the ECS, cannabinoid receptor 1 (CB1) and cannabinoid receptor 2 (CB2), were identified as the molecular targets of the phytocannabinoid Δ⁹-tetrahydrocannabinol (Δ⁹-THC). Restrictions on access to cannabis have eased worldwide, leading to a resurgence in interest in the therapeutic potential of cannabis. Much of the focus has been on the two major constituents, Δ⁹-THC and cannabidiol (CBD). Cannabis contains over 140 phytocannabinoids, although only a handful have been tested for pharmacological activity. Many of these minor cannabinoids potently modulate receptors, ionotropic channels, and enzymes associated with the ECS and show therapeutic potential individually or synergistically with other phytocannabinoids. The following review will focus on the pharmacological developments of the next generation of phytocannabinoid therapeutics.

Synthetic Access to Cannabidiol and Analogs as Active Pharmaceutical Ingredients

Cannabinoids have surely been one of the most widely self-administered drugs other than caffeine. The U.S. FDA recently approved one cannabinoid-based drug whose active pharmaceutical ingredient (API) is cannabidiol (CBD). The long history of individual use of cannabis for a wide range of conditions has sparked great interest in other uses of CBD, in ethical drugs and botanical supplements as well as in foods and nonprescription wellness products. CBD may be sourced from cannabis plants but can also be prepared synthetically, the topic of this review.

Integrating experimental and computational techniques to study chromatographic enantioresolutions of chiral tetrahydroindazole derivatives

With the selection of partially saturated 2H-indazoles as model compounds, we demonstrate the possibility to use Whelk-O1 chiral stationary phases (CSPs) to succeed in efficient small-scale preparative enantioseparations. Runs of three consecutive liquid chromatography injections (about 300 μg of racemate repeatedly injected in a 100 μL loop) produced groups of peaks without band contamination (α = 1.2 and R_S = 2.57). With this procedure approximately 3.0 mg of each enantiomer, with enantiomeric excess ≥ 97% were obtained. Very profitably, the high volatility of n-hexane used as the sole eluent facilitated the solvent evaporation after the enantiomer recovery. High resolution mass spectrometry analysis confirmed that the chemical identity of the two enantiomers was preserved along the entire process. The ability of Whelk-O1 phases in enantioseparating structurally similar compounds was confirmed with the analysis of other two racemates. Moreover, the relevant chemoselectivity exhibited by the CSP towards the three racemates should allow to simultaneously optimizing the enantioselectivity of different analytes and perform small-scale enantioresolutions of different compounds during the same run. In this study, the integration of experimental off-line electronic circular dichroism analysis with ab initio time-dependent density-functional theory simulations facilitated the assignment of the absolute configuration of the single enantiomers, while a molecular dynamics protocol can be useful to make a priori predictions of the enantioseparation ability of CSP towards selected compounds.

Cannabis sativa L. Inflorescences from Monoecious Cultivars Grown in Central Italy: An Untargeted Chemical Characterization from Early Flowering to Ripening

The chemical composition of the inflorescences from four Cannabis sativa L. monoecious cultivars (Ferimon, Uso-31, Felina 32 and Fedora 17), recently introduced in the Lazio Region, was monitored over the season from June to September giving indications on their sensorial, pharmaceutical/nutraceutical proprieties. Both untargeted (NMR) and targeted (GC/MS, UHPLC, HPLC-PDA/FD and spectrophotometry) analyses were carried out to identify and quantify compounds of different classes (sugars, organic acids, amino acids, cannabinoids, terpenoids, phenols, tannins, flavonoids and biogenic amines). All cultivars in each harvesting period showed a THC content below the Italian legal limit, although in general THC content increased over the season. Citric acid, malic acid and glucose showed the highest content in the late flowering period, whereas the content of proline drastically decreased after June in all cultivars. Neophytadiene, nerolidol and chlorogenic acid were quantified only in Felina 32 cultivar, characterized also by a very high content of flavonoids, whereas alloaromadendrene and trans-cinnamic acid were detected only in Uso-31 cultivar. Naringenin and naringin were present only in Fedora 17 and Ferimon cultivars, respectively. Moreover, Ferimon had the highest concentration of biogenic amines, especially in July and August. Cadaverine was present in all cultivars but only in September. These results suggest that the chemical composition of Cannabis sativa L. inflorescences depends on the cultivar and on the harvesting period. Producers can use this information as a guide to obtain inflorescences with peculiar chemical characteristics according to the specific use.

Cannabichromene

Cannabinochromene (CBC, 1a) is the archetypal member of a class of more than twenty isoprenylated 5-hydroxy-7-alkyl(aralky)benzo[2 H]pyranes first reported from Cannabis sativa L. but also occurring in unrelated plants ( Rhododendron species) as well as liverworts and fungi. The chemistry, synthesis, and bioactivity of CBC (1a) is reviewed, highlighting its underexploited pharmacological potential and rich chemistry.

Enantiomeric Mixtures in Natural Product Chemistry: Separation and Absolute Configuration Assignment

Chiral natural product molecules are generally assumed to be biosynthesized in an enantiomerically pure or enriched fashion. Nevertheless, a significant amount of racemates or enantiomerically enriched mixtures has been reported from natural sources. This number is estimated to be even larger since the enantiomeric purity of secondary metabolites is rarely checked in the natural product isolation pipeline. This latter fact may have drastic effects on the evaluation of the biological activity of chiral natural products. A second bottleneck is the determination of their absolute configurations. Despite the widespread use of optical rotation and electronic circular dichroism, most of the stereochemical assignments are based on empirical correlations with similar compounds reported in the literature. As an alternative, the combination of vibrational circular dichroism and quantum chemical calculations has emerged as a powerful and reliable tool for both conformational and configurational analysis of natural products, even for those lacking UV-Vis chromophores. In this review, we aim to provide the reader with a critical overview of the occurrence of enantiomeric mixtures of secondary metabolites in nature as well the best practices for their detection, enantioselective separation using liquid chromatography, and determination of absolute configuration by means of vibrational circular dichroism and density functional theory calculations.