A Novel C3/C4-Fused Indole Scaffold through Acid-Catalyzed Cascade Reaction.

3,4-bridged indoles are underrepresented among the vast number of indoles described in the literature. Attempts to access 3,4-macrocyclized indoles led to the unexpected formation of a novel tetracyclic indole through intramolecular acid-catalyzed ring contraction. The herein-established one-step synthetic route provides an excellent medicinal chemistry platform for the construction of screening libraries covering a unique chemical space of indoles.

Cold Physical Plasma-Mediated Fenretinide Prodrug Activation Confers Additive Cytotoxicity in Epithelial Cells.

Cold physical plasma is a partially ionized gas operated at body temperature and utilized for heat-sensitive technical and medical purposes. Physical plasma is a multi-component system consisting of, e.g., reactive species, ions and electrons, electric fields, and UV light. Therefore, cold plasma technology is an interesting tool for introducing biomolecule oxidative modifications. This concept can be extended to anticancer drugs, including prodrugs, which could be activated in situ to enhance local anticancer effects. To this end, we performed a proof-of-concept study on the oxidative prodrug activation of a tailor-made boronic pinacol ester fenretinide treated with the atmospheric pressure argon plasma jet kINPen operated with either argon, argon-hydrogen, or argon-oxygen feed gas. Fenretinide release from the prodrug was triggered via Baeyer-Villiger-type oxidation of the boron-carbon bond based on hydrogen peroxide and peroxynitrite, which were generated by plasma processes and chemical addition using mass spectrometry. Fenretinide activation led to additive cytotoxic effects in three epithelial cell lines in vitro compared to the effects of cold plasma treatment alone regarding metabolic activity reduction and an increase in terminal cell death, suggesting that cold physical plasma-mediated prodrug activation is a new direction for combination cancer treatment studies.

Advances in the discovery of new chemotypes through ultra-large library docking.

INTRODUCTION: The size and complexity of virtual screening libraries in drug discovery have skyrocketed in recent years, reaching up to multiple billions of accessible compounds. However, virtual screening of such ultra-large libraries poses several challenges associated with preparing the libraries, sampling, and pre-selection of suitable compounds. The utilization of artificial intelligence (AI)-assisted screening approaches, such as deep learning, poses a promising countermeasure to deal with this rapidly expanding chemical space. For example, various AI-driven methods were recently successfully used to identify novel small molecule inhibitors of the SARS-CoV-2 main protease (Mpro). AREAS COVERED: This review focuses on presenting various kinds of virtual screening methods suitable for dealing with ultra-large libraries. Challenges associated with these computational methodologies are discussed, and recent advances are highlighted in the example of the discovery of novel Mpro inhibitors targeting the SARS-CoV-2 virus. EXPERT OPINION: With the rapid expansion of the virtual chemical space, the methodologies for docking and screening such quantities of molecules need to keep pace. Employment of AI-driven screening compounds has already been shown to be effective in a range from a few thousand to multiple billion compounds, furthered by de novo generation of drug-like molecules without human interference.

Flucytosine-based prodrug activation by cold physical plasma.

Reactive oxygen species (ROS) are known to trigger drug release from arylboronate-containing ROS-responsive prodrugs. In cancer cells, elevated levels of ROS can be exploited for the selective activation of prodrugs via Baeyer-Villiger type oxidation rearrangement sequences. Here, we report a proof of concept to demonstrate that these cascades can as well be initiated by cold physical plasma (CPP). An analog of a recently reported fluorouracil prodrug based on the less toxic drug 5-fluorocytosine (5-FC) was synthesized with a view to laboratory safety reasons and used as a model compound to prove our hypothesis that CPP is suitable as a trigger for the prodrug activation. Although the envisioned oxidation and rearrangement with successive loss of boronic acid species could be achieved by plasma treatment, the anticipated spontaneous liberation of 5-FC was inefficient in the model case. However, the obtained results suggest that custom-tailored CPP-responsive prodrugs might become an evolving research field.

Crystal structure of 7,8,15,16,17-penta-thiadi-spiro-[5.2.59.36]hepta-deca-ne.

The title compound, C12H20S5, crystallizes in the monoclinic space group P21/c with four mol-ecules in the unit cell. In the crystal, the asymmetric unit comprises the entire mol-ecule with the three cyclic moieties arranged in a line. The mol-ecules in the unit cell pack in a parallel fashion, with their longitudinal axes arranged along a uniform direction. The packing is stabilized by the one-dimensional propagation of non-classical hydrogen-bonding contacts between the central sulfur atom of the S3 fragment and the C-H of a cyclo-hexyl group from a glide-related mol-ecule [C⋯S = 3.787 (2) Å].

Simultaneous quantification of acidic and basic flupirtine metabolites by supercritical fluid chromatography according to European Medicines Agency validation.

Supercritical fluid chromatography (SFC) holds the potential to become an orthogonal method to HPLC/UHPLC in xenobiotic metabolism studies, due to its outstanding capacity to simultaneously separate highly similar (as HPLC) and physicochemically different analytes (problematic using HPLC). Paucity of guideline-conform validation, however, has been a major obstacle to clinical application of SFC, even in cases where biotransformation yields chemically dissimilar metabolites that require more than one HPLC method for comprehensive analysis. Here, a method based on supercritical fluid chromatography coupled to single quadrupole MS detection was developed to simultaneously quantify the divisive analgesic flupirtine and its acidic and basic metabolites, represented by 4-fluorohippuric acid (4-FHA) and the active metabolite D-13223 respectively, using custom-made synthetic internal standards. Experimental data on the fundamental retention mechanisms under supercritical conditions, indicating the importance of halogen and π-π-bonding for specific retention on polysaccharide-based stationary-phases, is discussed. Compared to previous HPLC methods, the novel method offers higher versatility in terms of the target metabolite range (addressing both acidic and basic metabolites within a singular method), faster analysis (7.5 min), and compliance with green chemistry principles. Validation was performed according to EMA criteria on bioanalytical method validation, demonstrating selectivity, carry-over, calibration curve parameters (LLOQ, range, and linearity), within- and between-run accuracy and precision, dilution integrity, matrix effect and stability. For proof-of-concept, the SFC method was applied to clinical samples of human urine obtained after single intravenous (100 mg), single oral (100 mg), and repeated oral administration (400 mg). Flupirtine, D-13223, and 4-FHA could be quantified, shedding light on the extent of oxidative flupirtine metabolism in humans in the context of the unresolved biotoxification that has led to the withdrawal of specific neuronal KV7 openers.

Subcritical Fluid Chromatography at Sub-Ambient Temperatures for the Chiral Resolution of Ketamine Metabolites with Rapid-Onset Antidepressant Effects.

Chiral metabolites of ketamine exerting rapid-onset yet sustained antidepressant effects may be marketed directly in the future, but require chemo- and enantio-selective chromatographic methods for quality assurance and control. The chromatographic behavior of S-/R-ketamine, S-/R-norketamine, S-/R-dehydronorketamine, and (2R,6R)-/(2S,6S)-hydroxynorketamine in supercritical fluid chromatography (SFC) was investigated computationally and experimentally with the aim of identifying problematic pairs of enantiomers and parameters for chiral resolution. Retention on three different polysaccharide-based chiral stationary phases (Lux Amylose-2, i-Amylose-3, and i-Cellulose-5) provided new information on the significance of halogen atoms as halogen bond donors and hydrogen bond acceptors for enantioselectivity, which could be corroborated in silico by molecular docking studies. Modifiers inversely affected enantioselectivity and retention. Methanol yielded lower run times but superior chiral resolution compared to 2-propanol. Lower temperatures than those conventionally screened did not impair phase homogeneity but improved enantioresolution, at no cost to reproducibility. Thus, sub-ambient temperature subcritical fluid chromatography (SubFC), essentially low-temperature HPLC with subcritical CO2, was applied. The optimization of the SubFC method facilitated the chiral separation of ketamine and its metabolites, which was applied in combination with direct injection and online supercritical fluid extraction to determine the purity of pharmaceutical ketamine formulations for proof of concept.