An acid-free Pictet–Spengler reaction using deep eutectic solvents (DES)

Henlea earthworm bioluminescence comprises violet-blue BRET from tryptophan 2-carboxylate to deazaflavin cofactor

We recently identified the deazaflavin cofactor as a light emitter in novel bioluminescence (BL) system from Siberian earthworms Henlea sp. (Petushkov et al., 2023, Org. Biomol. Chem. 21:415-427). In the present communication we compared in vitro BL spectra in the absence and in the presence of the cofactor and found a wavelength shift from 420 to 476 nm. This violet-blue BRET to deazaflavin cofactor (acceptor of photonless transfer) masks the actual oxyluciferin as an emitter (BRET donor) in the novel BL system. The best candidate for that masked chromophore is tryptophan 2-carboxylate (T2C) found previously as a building block in some natural products isolated from Henlea sp. (Dubinnyi et al., 2020, ChemSelect 5:13155-13159). We synthesized T2C and acetyl-T2C, verified their presence in earthworms by nanoflow-HRMS, explored spectral properties of excitation and emission spectra and found a chain of excitation/emission maxima with a perfect potential for BRET: 300 nm (excitation of T2C) - 420 nm (emission of T2C) - 420 nm (excitation of deazaflavin) - 476 nm (emission of deazaflavin, BL). An array of natural products with T2C chromophore are present in BL earthworms as candidates for novel oxyluciferin. We demonstrated for the Henlea BL that the energy of the excited state of the T2C chromophore is transferred by the Förster mechanism and then emitted by deazaflavin (BRET), similarly to known examples: aequorin-GFP in Aequorea victoria and antenna proteins in bacterial BL systems (lumazine from Photobacterium and yellow fluorescent protein from Vibrio fischeri strain Y1).

Clean Synthetic Strategies to Biologically Active Molecules from Lignin: A Green Path to Drug Discovery

Deriving active pharmaceutical agents from renewable resources is crucial to increasing the economic feasibility of modern biorefineries and promises to alleviate critical supply-chain dependencies in pharma manufacturing. Our multidisciplinary approach combines research in lignin-first biorefining, sustainable catalysis, and alternative solvents with bioactivity screening, an in vivo efficacy study, and a structural-similarity search. The resulting sustainable path to novel anti-infective, anti-inflammatory, and anticancer molecules enabled the rapid identification of frontrunners for key therapeutic indications, including an anti-infective against the priority pathogen Streptococcus pneumoniae with efficacy in vivo and promising plasma and metabolic stability. Our catalytic methods provided straightforward access, inspired by the innate structural features of lignin, to synthetically challenging biologically active molecules with the core structure of dopamine, namely, tetrahydroisoquinolines, quinazolinones, 3-arylindoles and the natural product tetrahydropapaveroline. Our diverse array of atom-economic transformations produces only harmless side products and uses benign reaction media, such as tunable deep eutectic solvents for modulating reactivity in challenging cyclization steps.

Insights into the relationships between physicochemical properties, solvent performance, and applications of deep eutectic solvents

Deep eutectic solvent (DES) is regarded as a new generation of green solvent due to its distinctive and tailorable physicochemical properties, such as low volatility, strong solubility, biodegradability, low-cost, environment-friendly, and feasibility of the structural design. As an alternative to traditional organic solvents and ionic liquids (ILs), DESs have been widely applied in many fields, such as organic chemical synthesis, electrochemical deposition, material preparation, biomass catalytic conversion, extraction and separation, detection and analysis, nanotechnology, gas absorption, and drug delivery. In this paper, through in-depth discussion on factors influencing the physicochemical properties of DESs, we summarized the relations between their composition, structure, and performance. Focusing on their solvent performance, we analyzed the latest research results of DESs with different physicochemical properties in various fields. It should be pointed out that designing and synthesizing DESs from the molecular structure aspect to regulate their physicochemical properties is the direction of accurately developing new functional applications of DESs.

Design and synthesis of β-carboline and combretastatin derivatives as anti-neutrophilic inflammatory agents

A series of β-carboline derivatives was synthesized by the Pictet-Spengler reaction with or without the combretastatin skeleton. The structures of these derivatives were elucidated by spectroscopic techniques. All synthesized compounds were evaluated for their anti-inflammatory activity in human neutrophils. Among them, two compounds, NTU-228 and HK-72, showed significant inhibitory effects on N-formyl-Met-Leu-Phe (fMLF)-induced superoxide anion generation in human neutrophils with IC₅₀ values of 5.58 ± 0.56 and 2.81 ± 0.07 μM, respectively. Neither NTU-228 nor HK-72 caused cytotoxicity in human neutrophils. NTU-228 inhibited the phosphorylation of p38 mitogen-activated protein kinase (MAPK) and intracellular Ca²⁺ levels ([Ca²⁺]_i) in fMLF-activated human neutrophils. Additionally, HK-72 selectively inhibited the fMLF-induced phosphorylation of p38 and [Ca²⁺]_i in human neutrophils. Molecular docking analysis showed a favorable binding affinity of HK-72 toward p38 MAPK. The proposed synthetic strategy opens up new opportunities for the synthesis of novel potential candidates against neutrophilic inflammation.

Preparation of eco-friendly composite food packaging films based on gelatin and a matrine coconut acids ionic liquid

Eco-friendly food packaging films were prepared by compositing gelatin with a bioactive ionic liquid showing excellent antioxidant and antibacterial properties.

Selective construction of alkaloid scaffolds by alcohol-based direct and mild aerobic oxidative Pictet–Spengler reactions

Tetrahydro-β-carboline and β-carboline alkaloid scaffolds can be selectively obtained by direct aerobic oxidative Pictet–Spengler reactions of tryptamines with alcohols using TBN/TEMPO as the catalysts and oxygen as the oxidant under mild conditions.

From Wood to Tetrahydro-2-benzazepines in Three Waste-Free Steps: Modular Synthesis of Biologically Active Lignin-Derived Scaffolds

Inherently complex, lignin-derived aromatic monomers comprising valuable structural moieties present in many pharmaceuticals would serve as ideal substrates for the construction of biologically active molecules. Here, we describe a strategy that incorporates all intrinsic functional groups present in platform chemicals obtained by lignin depolymerization into value-added amines, using sustainable catalytic methods and benign solvents. Our strikingly efficient protocol provides access to libraries of aminoalkyl-phenol derivatives and seven-membered N-heterocycles directly from wood in two, respectively three, waste-free steps. Several molecules in these libraries have shown promising antibacterial or anticancer activities, emphasizing the advantage of this modular synthetic strategy and the potential for drug discovery. The sustainable catalytic pathways presented here can lead to significant benefits for the pharmaceutical industry where reduction of hazardous waste is a prime concern, and the described strategies that lead to high-value products from non-edible biomass waste streams also markedly increase the economic feasibility of lignocellulosic biorefineries.

Natural deep eutectic solvents for lignocellulosic biomass pretreatment: Recent developments, challenges and novel opportunities

Conversion of lignocellulosic biomass to fuels and chemicals has attracted immense research and development around the world. Lowering recalcitrance of biomass in a cost-effective manner is a challenge to commercialize biomass-based technologies. Deep eutectic solvents (DESs) are new 'green' solvents that have a high potential for biomass processing because of their low cost, low toxicity, biodegradability, easy recycling and reuse. This article discusses the properties of DESs and recent advances in their application for lignocellulosic biomass processing. The effectiveness of DESs in hydrolyzing lignin-carbohydrate complexes, removing lignin/hemicellulose from biomass as well as their effect on biomass deconstruction, crystallinity and enzymatic digestibility have been discussed. Moreover, this review presents recent findings on the compatibility of natural DESs with enzymes and microorganisms.

Application of Pictet-Spengler Reaction to Indole-Based Alkaloids Containing Tetrahydro-β-carboline Scaffold in Combinatorial Chemistry

Indole-based alkaloids are well-known in the literature for their diverse biological properties. Polysubstituted optically active tetrahydro-β-carboline derivatives functionalized on C-1 position are the common structural motif in most of the indole-based alkaloids, as well as highly marketed drugs. The stereoselective Pictet-Spengler reaction is one of the currently most important synthetic techniques used for the preparation of these privileged tetrahydro-β-carboline scaffolds. To date, there are numerous research reports that have been published on the synthesis of the tetrahydro-β-carboline scaffold both on solid phase, as well as in solution phase. Moreover rapid growth has been observed for the enantioselective synthesis of tetrahydro-β-carboline scaffold using chiral organocatalysts. In this Review, efforts have been taken to shed light on the latest information available on different strategies to synthesize tetrahydro-β-carboline both on solid phase and in solution phase during the last 20 years. Furthermore, we believe that the present synthetic methodologies covered in this Review will help to improve the status of this privileged tetrahydro-β-carboline scaffold in its use for drug discovery.

Evaluation of sodium acetate trihydrate–urea DES as a benign reaction media for the Biginelli reaction. Unexpected synthesis of methylenebis(3-hydroxy-5,5-dimethylcyclohex-2-enones), hexahydroxanthene-1,8-diones and hexahydroacridine-1,8-diones

In this work, the low melting mixture sodium acetate trihydrate–urea was synthesized and the eutectic composition was determined and characterized. The performance of this deep eutectic solvent on the Biginelli reaction was evaluated.

Ferrier reaction in a deep eutectic solvent

A mild and efficient synthesis of 2,3-unsaturated sugar derivatives has been achieved by conducting the Ferrier reaction in a deep eutectic solvent (DES). A wide range of alcohols including primary, secondary, benzylic, and sugar-derived primary alcohols can be used. Advantages include good yields, shorter reaction times and recyclability of DES.

Recent advances in the application of deep eutectic solvents as sustainable media as well as catalysts in organic reactions

This review highlights the recent advances using deep eutectic solvents (DESs), deep eutectic ionic liquids (DEILs), low-melting mixtures (LMMs) or low transition temperature mixtures (LTTMs) as green media as well as catalysts in organic reactions.