Catalytic asymmetric synthesis of cannabinoids and menthol from neral

Stereoisomers of cannabidiols and their pharmacological activities - A potentially novel direction for cannabinoids

Cannabidiol (CBD), a bicyclic non-psychoactive cannabinoid biosynthesized by Cannabis spp. of plants, has attracted significant interest in the past decade due to its therapeutic properties. In 2018, the US FDA approved Epidiolex®, a CBD-based drug for the treatment of two rare epileptic seizure disorders. CBD possesses two chiral centers at C3 and C4 on its terpenoid moiety and exhibits cis-trans stereoisomerism along the C3-C4 bond axis. (-)-trans-(3R,4R)-CBD, the natural CBD, is biosynthesized by the cannabis plant, while the unnatural (+)-trans-(3S,4S)-CBD is obtained via chemical synthesis. Both trans isomers exhibit broad in vitro and in vivo biological activities; typically, the unnatural stereoisomer (+)-trans-CBD and its derivatives exhibited more potent activities in comparison to the corresponding (-)-trans isomers. On the other hand, cis-CBD isomers have only been reported recently and can undergo epimerization into trans isomers. There is a significant opportunity to explore unique synthetic methods and biological activities of stereoisomers of CBD that may pave the path for the development of novel therapeutics. Herein, as a novel direction in cannabinoids, we review the chemistry of CBD stereoisomers, their structure-activity relationships, target selectivity and efficacy in animal models.

Synthesis of (-)-Cannabidiol (CBD), (-)-Δ9- and (-)-Δ8-Tetrahydrocannabinols, Encapsulation of CBD with Nanoparticles for Controlled Delivery and Biological Evaluation

Cannabidiol (CBD) is garnering increasing interest due to its significant biological activity. This natural compound is one of the major cannabinoids in Cannabis sativa L. In this work, we describe the encapsulation of CBD in solid and hollow pH-sensitive poly(4-vinylpyridine) (solid@p4VP and hollow@p4VP) nanoparticles, and temperature-sensitive poly(N-isopropylacrylamide) (solid@pNIPAM and hollow@pNIPAM) nanoparticles for transport and release CBD in a controlled manner. The CBD loading into these smart polymeric systems was effective and their release profiles, solubility and resistance to stomach and intestinal conditions were evaluated, showing satisfactory properties and improved bioavailability with respect to free CBD. Finally, the A549 human lung cancer cell line was used as lung adenocarcinoma epithelial cellular model to carry out preliminary assays of the in vitro activity of the vehiculized CBD. For all these studies, synthetic CBD was employed, for which a new efficient and scalable synthesis of cannabinoids has been developed.

Proline-Functionalized Magnetic Nanoparticles as Highly Performing Asymmetric Catalysts

Amino acids have a crucial role in the field of asymmetric organocatalysis for the production of chiral compounds with high added value and specific biological activity. In particular, proline offers high activity and stereoselectivity for catalyzing aldol reactions in organic solvents. However, proline-based catalysts often lack water-solubility, accessibility, catalytic performance, or recovery in aqueous media. This work reports the design of proline-functionalized poly(methyl methacrylate) (PMMA) nanoparticles with a magnetic core that offer high availability of chiral units in water and high recyclability. A proline-based copolymerizable surfactant is designed and integrated onto the surface of PMMA nanoparticles through a miniemulsion polymerization process without using additional surfactants. The miniemulsion technique allows the incorporation of magnetite to the system to create a magnetically separable catalyst. The chiral nanocatalyst presents a high diastereoselective catalytic activity for the intermolecular aldol reaction between p-nitrobenzaldehyde and cyclohexanone in water.

Emerging Conformational-Analysis Protocols from the RTCONF55-16K Reaction Thermochemistry Conformational Benchmark Set

RTCONF55-16K is a new, reactive conformational data set based on cost-efficient methods to assess different conformational analysis protocols. Our reference calculations underpinned the accuracy of the CENSO (Grimme et al. J. Phys. Chem. A, 2021, 125, 4039) procedure and resulted in alternative recipes with different cost-accuracy compromises. Our general-purpose and economical protocols (CENSO-light and zero, respectively) were found to be 10-30 times faster than the original algorithm, adding only 0.4-0.7 kcal/mol absolute error to the relative free energy estimates.

Asymmetric Synthesis of (-)-Cannabidiol (CBD), (-)-Δ9-Tetrahydrocannabinol (Δ9-THC) and Their cis Analogs Using an Enantioselective Organocatalyzed Diels-Alder Reaction

Herein we describe an asymmetric synthesis of the pharmacologically relevant natural (-)-trans-CBD and psychoactive (-)-trans-Δ9-THC, as well as their synthetic cis diastereomers. The key step is an enantioselective Diels-Alder reaction catalyzed by a prolinol-based catalyst, which provides the cyclohexene carbaldehyde intermediate in good yield and high enantiomeric excess. Optimization of the substituted resorcinol protecting groups to avoid harsh and low-yield deprotection of the acid sensitive resorcinol moiety is also described.

Real-Time Direct Monitoring of Chirality Fixation and Recognition at the Single-Molecule Level

Chirality, a fundamental attribute of nature, significantly influences a wide range of phenomena related to physical properties, chemical reactions, biological pharmacology, and so on. As a pivotal aspect of chirality research, chirality recognition contributes to the synthesis of complex chiral products from simple chiral compounds and exhibits intricate interplay between chiral materials. However, macroscopic detection technologies cannot unveil the dynamic process and intrinsic mechanisms of single-molecule chirality recognition. Herein, we present a single-molecule detection platform based on graphene-molecule-graphene single-molecule junctions to measure the chirality recognition involving interactions between amines and chiral alcohols. This approach leads to the realization of in situ and real-time direct observation of chirality recognition at the single-molecule level, demonstrating that chiral alcohols exhibit compelling potential to induce the formation of the corresponding chiral configuration of molecules. The amalgamation of theoretical analyses with experimental findings reveals a synergistic action between electrostatic interactions and steric hindrance effects in the chirality recognition process, thus substantiating the microscopic mechanism governing the chiral structure-activity relationship. These studies open up a pathway for exploring novel chiral phenomena from the fundamental limits of chemistry, such as chiral origin and chiral amplification, and offer important insights into the precise synthesis of chiral materials.

Hydroxymethylation hydroxylation of 1,3-diarylpropene through a catalytic diastereoselective Prins reaction: cyclization logic and access to brazilin core

A catalytic diastereoselective Prins reaction for hydroxymethylation and hydroxylation of 1,3-diarylpropene was successfully utilized to prepare various 1,3-dioxanes 7 in 14-88% yields. Take advantage of the synthetic intermediate 7h, the key B/C rings in brazilin core could be constructed by the sequential of Friedel-Crafts/Ullmann-Ma rather than Ullmann-Ma/Friedel-Crafts reactions.

Zn Single-Atom Catalysts Enable the Catalytic Transfer Hydrogenation of α,β-Unsaturated Aldehydes

Highly active nonprecious-metal single-atom catalysts (SACs) toward catalytic transfer hydrogenation (CTH) of α,β-unsaturated aldehydes are of great significance but still are deficient. Herein, we report that Zn-N-C SACs containing Zn-N3 moieties can catalyze the conversion of cinnamaldehyde to cinnamyl alcohol with a conversion of 95.5% and selectivity of 95.4% under a mild temperature and atmospheric pressure, which is the first case of Zn-species-based heterogeneous catalysts for the CTH reaction. Isotopic labeling, in situ FT-IR spectroscopy, and DFT calculations indicate that reactants, coabsorbed at the Zn sites, proceed CTH via a "Meerwein-Ponndorf-Verley" mechanism. DFT calculations also reveal that the high activity over Zn-N3 moieties stems from the suitable adsorption energy and favorable reaction energy of the rate-determining step at the Zn active sites. Our findings demonstrate that Zn-N-C SACs hold extraordinary activity toward CTH reactions and thus provide a promising approach to explore the advanced SACs for high-value-added chemicals.

Specific Discrimination Polymerization for Highly Isotactic Polyesters Synthesis

Isotactic polymers have emerged with unique and excellent properties in material sciences. Specific discrimination polymerization provides an ideal pathway to achieve highly isotactic polymers from their racemic monomers, which is of great significance and a challenge in polymeric chemistry. Although an enantioselective catalyst-mediated asymmetric kinetic resolution polymerization (AKRP) process makes it possible, a general and well-defined strategy for catalyst design is still rarely reported. Here, based on a novel dual-ligand strategy, a new type of chiral (BisSalen)Al complex with high enantioselectivity has been described, in which perfect AKRP of racemic phenethylglycolide (Pegl) is achieved for the first time. The more confined asymmetric microenvironment formed by a dual ligand is the key to improve the enantioselectivity of the original catalyst. To illustrate the generality of this strategy, a series of (BisSalen)Al complexes with homo- or heterodual ligands were designed for the AKRP of Pegl.

Rhodium-Catalyzed Asymmetric Addition to 4- or 5-Carbonyl-cycloenones through Dynamic Kinetic Resolution: Enantioselective Synthesis of (-)-Cannabidiol

The reaction of 4/5-carbonyl-cycloalkenone 1 or its achiral isomer 1' with organoboronic acid 2 in the presence of a chiral diene (S,S)-Fc-tfb-rhodium catalyst gave disubstituted trans-cycloalkanone 3 with high diastereo- and enantioselectivity. This highly efficient dynamic kinetic resolution is achieved by fast racemization of 1 through the formation of a dienolate followed by kinetic resolution with the chiral catalyst. The utility is demonstrated by the synthesis of key intermediates en route to (-)-cannabidiol.

Piers-Rubinsztajn reaction to unlock an 8-step synthesis of 7-hydroxy cannabidiol

A scalable synthesis of 7-hydroxy cannabidiol (7-OH CBD), a primary metabolite of (-)-cannabidiol (CBD), is highly desirable, from an industrial point of view, to enable future clinical trials. A Piers-Rubinsztajn reaction was key to enable a mild deprotection and a concise synthesis of 7-OH CBD from commercially available CBD, in 31% overall yield.

Development of an efficient yeast platform for cannabigerolic acid biosynthesis

Cannabinoids are important therapeutical molecules for human ailments, cancer treatment, and SARS-CoV-2. The central cannabinoid, cannabigerolic acid (CBGA), is generated from geranyl pyrophosphate and olivetolic acid by Cannabis sativa prenyltransferase (CsPT4). Despite efforts to engineer microorganisms such as Saccharomyces cerevisiae (S. cerevisiae) for CBGA production, their titers remain suboptimal because of the low conversion of hexanoate into olivetolic acid and the limited activity and stability of the CsPT4. To address the low hexanoate conversion, we eliminated hexanoate consumption by the beta-oxidation pathway and reduced its incorporation into fatty acids. To address CsPT4 limitations, we expanded the endoplasmic reticulum and fused an auxiliary protein to CsPT4. Consequently, the engineered S. cerevisiae chassis showed a marked improvement of 78.64-fold in CBGA production, reaching a titer of 510.32 ± 10.70 mg l-1 from glucose and hexanoate.

Concerted Hydrosilylation Catalysis by Silica-Immobilized Cyclic Carbonates and Surface Silanols

Developing a method for creating a novel catalysis of organic molecules is essential because of the growing interest in organocatalysis. In this study, we found that cyclic carbonates immobilized on a nonporous or mesoporous silica support showed catalytic activity for hydrosilylation, which was not observed for the free cyclic carbonates, silica supports, or their physical mixture. Analysis of the effects of linker lengths and pore sizes on the catalytic activity and carbonate C=O stretching frequency revealed that the proximity of carbonates and surface silanols was crucial for synergistic hydrosilylation catalysis. A carbonate and silanol concertedly activated the silane and aldehyde for efficient hydride transfer. Density functional theory calculations on a model reaction system demonstrated that both the carbonate and silanol contributed to the stabilization of the transition state of hydride transfer, which resulted in a reasonable barrier height of 16.8 kcal mol-1. Furthermore, SiO2/carbonate(C4) enabled the hydrosilylation of an aldehyde with an amino group without catalyst poisoning, owing to the weak acidity of surface silanols, in sharp contrast to previously developed acid catalysts. This study demonstrates that immobilization on a solid support can convert inactive organic molecules into active and heterogeneous organocatalysts.

Synthesis of Neocannabinoids Using Controlled Friedel-Crafts Reactions

A one-step transformation to produce 8,9-dihydrocannabidiol (H2CBD) and related "neocannabinoids" via controlled Friedel-Crafts reactions is reported. Experimental and computational studies probing the mechanism of neocannabinoid synthesis from cyclic allylic alcohol and substituted resorcinol reaction partners provide understanding of the kinetic and thermodynamic factors driving regioselectivity for the reaction. Herein, we present the reaction scope for neocannabinoid synthesis including the production of both normal and abnormal isomers under both kinetic and thermodynamic control. Discovery and optimization of this one-step protocol between various allylic alcohols and resorcinol derivatives are discussed and supported with density functional theory calculations.

Synthetic Pathways to Non-Psychotropic Phytocannabinoids as Promising Molecules to Develop Novel Antibiotics: A Review

Due to the rapid emergence of multi drug resistant (MDR) pathogens against which current antibiotics are no longer functioning, severe infections are becoming practically untreatable. Consequently, the discovery of new classes of effective antimicrobial agents with novel mechanism of action is becoming increasingly urgent. The bioactivity of Cannabis sativa, an herbaceous plant used for millennia for medicinal and recreational purposes, is mainly due to its content in phytocannabinoids (PCs). Among the 180 PCs detected, cannabidiol (CBD), Δ⁸ and Δ⁹-tetrahydrocannabinols (Δ⁸-THC and Δ⁹-THC), cannabichromene (CBC), cannabigerol (CBG), cannabinol (CBN) and some of their acidic precursors have demonstrated from moderate to potent antibacterial effects against Gram-positive bacteria (MICs 0.5-8 µg/mL), including methicillin-resistant Staphylococcus aureus (MRSA), epidemic MRSA (EMRSA), as well as fluoroquinolone and tetracycline-resistant strains. Particularly, the non-psychotropic CBG was also capable to inhibit MRSA biofilm formation, to eradicate even mature biofilms, and to rapidly eliminate MRSA persiter cells. In this scenario, CBG, as well as other minor non-psychotropic PCs, such as CBD, and CBC could represent promising compounds for developing novel antibiotics with high therapeutic potential. Anyway, further studies are necessary, needing abundant quantities of such PCs, scarcely provided naturally by Cannabis plants. Here, after an extensive overture on cannabinoids including their reported antimicrobial effects, aiming at easing the synthetic production of the necessary amounts of CBG, CBC and CBD for further studies, we have, for the first time, systematically reviewed the synthetic pathways utilized for their synthesis, reporting both reaction schemes and experimental details.