Spirocyclic compounds: potential drug leads in the fight against Mycobacterium tuberculosis

TB drug discovery needs scientists' attention since drug resistance in TB, including extensively drug-resistant TB (XDR-TB) and multidrug-resistant TB (MDR-TB), is a major healthcare concern. Since millions of fatalities from tuberculosis are recorded each year, there is an urgent need to discover new anti-tubercular medications that will either eradicate or control the disease. Spiro compounds have garnered a lot of attention in medicinal chemistry these days because of various biological activities mainly because of their adaptability and structural resemblance to significant pharmacophores. This article overviews the synthesis and activity of spirocyclic compounds as anti-tubercular agents. Both synthesized and naturally occurring spiro chemicals exhibit antitubercular properties. The promising antitubercular potential shown by some of the spirocyclic compounds has attracted scientists to explore them further to develop molecules with improved pharmacodynamic and pharmacokinetic properties and new mechanisms of action with enhanced safety and efficacy in tuberculosis. The current review covers the exploration of spiro compounds from the year 2004 to 2024 for the combat of Tuberculosis. This review gives the comprehensive advancements in this scaffold which would help the logical design of powerful, less toxic, and more effective spirocyclic anti-TB medicinal molecules.

Spectral Assignment in the [3 + 2] Cycloadditions of Methyl (2E)-3-(Acridin-4-yl)-prop-2-enoate and 4-[(E)-2-Phenylethenyl]acridin with Unstable Nitrile N-Oxides

The investigation of cycloaddition reactions involving acridine-based dipolarophiles revealed distinct regioselectivity patterns influenced mainly by the electronic factor. Specifically, the reactions of methyl-(2E)-3-(acridin-4-yl)-prop-2-enoate and 4-[(1E)-2-phenylethenyl]acridine with unstable benzonitrile N-oxides were studied. For methyl-(2E)-3-(acridin-4-yl)-prop-2-enoate, the formation of two regioisomers favoured the 5-(acridin-4-yl)-4,5-dihydro-1,2-oxazole-4-carboxylates, with remarkable exclusivity in the case of 4-methoxybenzonitrile oxide. Conversely, 4-[(1E)-2-phenylethenyl]acridine displayed reversed regioselectivity, favouring products 4-[3-(substituted phenyl)-5-phenyl-4,5-dihydro-1,2-oxazol-4-yl]acridine. Subsequent hydrolysis of isolated methyl 5-(acridin-4-yl)-3-phenyl-4,5-dihydro-1,2-oxazole-4-carboxylates resulted in the production of carboxylic acids, with nearly complete conversion. During NMR measurements of carboxylic acids in CDCl3, decarboxylation was observed, indicating the formation of a new prochiral carbon centre C-4, further confirmed by a noticeable colour change. Overall, this investigation provides valuable insights into regioselectivity in cycloaddition reactions and subsequent transformations, suggesting potential applications across diverse scientific domains.

Synthesis and antihepatoma activity of guaianolide dimers derived from lavandiolide I

Guaianolide dimers represent a unique class of natural products with anticancer activities, but their low content in plants has limited in-depth pharmacological studies. Lavandiolide I is a guaianolide dimer isolated from Artemisia species, and had been synthesized on a ten-gram scale in four steps with 60 % overall yield, which showed potent antihepatoma activity on the HepG2, Huh7, and SK-Hep-1 cell lines with IC50 values of 12.1, 18.4, and 17.6 µM, respectively. To explore more active dimers, 33 lavandiolide I derivatives were designed, synthesized, and evaluated for their inhibitory activity on human hepatoma cell lines. Among them, 10 derivatives were more active than lavandiolide I and sorafenib on the three cell lines. The primary structure-activity relationship concluded that the introduction of aldehyde, ester, azide, amide, carbamate and urea functional groups at C-14' of the guaianolide dimer significantly enhanced the antihepatoma activity. Among these compounds, derivatives 25, 27, and 33 enhanced antihepatoma activity more than 1.2-5.8 folds than that of lavandiolide I, and demonstrated low toxicity to the human liver cell lines (THLE-2) and good safety profiles with selective index ranging from 1.3 to 3.4, while lavandiolide I was more toxic to THLE-2 cells. This work provides new insights into enhancing the antihepatoma efficacy and reducing the toxicity of sesquiterpenoid dimers.

Recent advances in microwave-assisted multicomponent synthesis of spiro heterocycles

Spiro heterocycle frameworks are a class of organic compounds that possesses unique structural features making them highly sought-after targets in drug discovery due to their diverse biological and pharmacological activities. Microwave-assisted organic synthesis has emerged as a powerful tool for assembling complex molecular architectures. The use of microwave irradiation in synthetic chemistry is a promising method for accelerating reaction rates and improving yields. This review provides insights into the current state of the art and highlights the potential of microwave-assisted multicomponent reactions in the synthesis of novel spiro heterocyclic compounds that were reported between 2017 and 2023.

A new specific method for isolation of tomentosin with a high yield from Inula viscosa (L.) and determination of its bioactivities

INTRODUCTION

Tomentosin, the characteristic component of Inula viscosa (L.) is an important sesquiterpene lactone with anticarcinogenic effects. Methods of obtaining pure tomentosin are not sufficient for anticancer drug research.

OBJECTIVES

This study aims to develop a specific method to isolate tomentosin from I. viscosa with high yield. It also aims to investigate the inhibitory effects of tomentosin on human carbonic anhydrase I (hCAI), human carbonic anhydrase II (hCAII), acetylcholinesterase (AChE), butyrylcholinesterase (BChE), α-glucosidase, and α-amylase enzymes.

MATERIAL AND METHODS

Tomentosin was purified by a specific column chromatography method. The content of tomentosin in dichloromethane, dichloromethane by Soxhlet method, ethanol and ethanol by Soxhlet method extracts of I. viscosa was determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Half maximal inhibitory concentration (IC₅₀ ) and inhibition constant (K_i ) values were calculated to determine in vitro enzyme inhibition effects.

RESULTS

Tomentosin was isolated in high yield (0.64%). The IC₅₀ and K_i values for tomentosin were calculated as 5.00 ± 0.19 (r = 0.9688) and 4.62 ± 0.10 μM for hCAI, 5.40 ± 0.26 (r = 0.9677) and 5.22 ± 0.31 μM for hCAII, 6.75 ± 0.208 (r = 0.9891) and 3.75 ± 0.27 μM for AChE, 6.67 ± 0.307 (r = 0.9820) and 0.51 ± 0.11 μM for BChE, 26.61 ± 0.236 (r = 0.9815) and 2.61 ± 0.71 μM for α-glucosidase and 26.89 ± 1.54 μM (r = 0.9670) for α-amylase, respectively.

CONCLUSION

Tomentosin was isolated in high yield from the paste-like extract of I. viscosa compared to the positive controls, it was determined that tomentosin was weakly effective against hCAI, hCAII, AChE and BChE, but thoroughly effective against α-glucosidase and α-amylase. These results suggested that tomentosin has α-glucosidase and α-amylase inhibitor potential.

Ethyl Acetate Fraction of Helianthus tuberosus L. Induces Anti-Diabetic, and Wound-Healing Activities in Insulin-Resistant Human Liver Cancer and Mouse Fibroblast Cells

Traditional, complementary, and integrative medicine are globally accepted alternative methods for the treatment of diabetes mellitus (DM). However, the mechanism of anti-diabetic effects of Helianthus tuberosus L. remains unproven. In the present study, antioxidant and anti-diabetic activity of the tubers of H. tuberosus were studied in detail. Methanolic extracts of H. tuberosus tubers were subjected to solvent fractionation method by increasing the polarity of the solvent using n-hexane, and ethyl acetate. The obtained methanol extracts and its fractions were subjected to free radical scavenging activity (DPPH and ABTS assay) and in vitro enzyme (α-amylase and α-glucosidase) inhibition assay. Moreover, glucose uptake in insulin-resistant HepG2 cell line was analyzed. The preliminary phytochemical analysis confirmed the presence of phenolic and flavonoid compounds in the active fraction. The radical scavenging and in vitro diabetic related enzyme inhibitory activities were found to be dose dependent. The maximum ABTS⁺ and DPPH scavenging activity was documented in ethyl acetate fraction of the H. tuberosus followed by methanol extract, hexane fraction, and methanol fraction. We also found that H. tuberosus showed a less toxicity in mouse fibroblast cells and enhance the glucose uptake in insulin-resistant HepG2 cells. Besides, the ethyl acetate fraction of the H. tuberosus analyzed by UPLC-QTOF-MS-MS and GC/MS revealed the presence of phenolic compounds such as neochlorogenic acid, chlorogenic acid, caffeic acid, 5-O-(4-coumaroyl)-quinic acid, feruloylquinic acid, caffeoylquinic acid, isoxazolidine, salicylic acid β-D-glucoside, dicaffeoylquinic acid isomers, salvianolic acid derivative isomers, and 1,4 dicaffeoylquinic acid etc. Among the identified phytochemicals, six were chosen for molecular docking study to explore their its inhibitory interactions with α-amylase and α-glucosidase. Taken together, the findings of the present study suggested that phytocompounds of EAF were responsible for the significant in vitro antioxidant, wound-healing, and anti-diabetic activities.

Understanding the Origin of the Regioselectivity in Non-Polar [3+2] Cycloaddition Reactions through the Molecular Electron Density Theory

The regioselectivity in non-polar [3+2] cycloaddition (32CA) reactions has been studied within the Molecular Electron Density Theory (MEDT) at the B3LYP/6-311G(d,p) level. To this end, the 32CA reactions of nine simplest three-atom-components (TACs) with 2-methylpropene were selected. The electronic structure of the reagents has been characterized through the Electron Localisation Function (ELF) and the Conceptual DFT. The energy profiles of the two regioisomeric reaction paths and ELF topology of the transition state structures are studied to understand the origin of the regioselectivity in these 32CA reactions. This MEDT study permits to conclude that the least electronegative X1 end atom of these TACs controls the asynchronicity in the C−X (X=C, N, O) single bond formation, and consequently, the regioselectivity. This behaviour is a consequence of the fact that the creation of the non-bonding electron density required for the formation of the new single bonds has a lower energy demand at the least electronegative X1 atom than at the Z3 one.

Synthesis and biological evaluation of fluoro-substituted spiro-isoxazolines as potential anti-viral and anti-cancer agents

Electrophilic fluorine-mediated dearomative spirocyclization has been developed to synthesize a range of fluoro-substituted spiro-isoxazoline ethers and lactones. The in vitro biological assays of synthesized compounds were probed for anti-viral activity against human cytomegalovirus (HCMV) and cytotoxicity against glioblastomas (GBM6) and triple negative breast cancer (MDA MB 231). Interestingly, compounds 4d and 4n showed significant activity against HCMV (IC50 ∼ 10 μM), while 4l and 5f revealed the highest cytotoxicity with IC50 = 36 to 80 μM. The synthetic efficacy and biological relevance offer an opportunity to further drug-discovery development of fluoro-spiro-isoxazolines as novel anti-viral and anti-cancer agents.

Theoretical analysis of the regio- and stereoselective synthesis of spiroisoxazolines

The [3+2] cycloaddition (32CA) reaction of benzonitrile oxide to α-methylene cyclopentanone and propionitrile oxide to γ-methyl-α-methylene-γ-butyrolactone, yielding regio- and stereochemically defined spiroisoxazolines, has been studied at the MPWB1K/6-311G(d,p) computational level. These processes proceed by a one-step mechanism through asynchronous transition states. Ortho regioselectivity and anti diastereofacial selectivity are predicted in complete agreement with the experimental outcomes.

A Molecular Electron Density Theory Study of the Chemoselectivity, Regioselectivity, and Diastereofacial Selectivity in the Synthesis of an Anticancer Spiroisoxazoline derived from α-Santonin

The [3 + 2] cycloaddition (32CA) reaction of an α-santonin derivative, which has an exocyclic C–C double bond, with p-bromophenyl nitrile oxide yielding only one spiroisoxazoline, has been studied within the molecular electron density theory (MEDT) at the MPWB1K/6-311G(d,p) computational level. Analysis of the conceptual density functional theory (CDFT) reactivity indices and the global electron density transfer (GEDT) account for the non-polar character of this zwitterionic-type 32CA reaction, which presents an activation enthalpy of 13.3 kcal·mol⁻¹. This 32CA reaction takes place with total ortho regioselectivity and syn diastereofacial selectivity involving the exocyclic C–C double bond, which is in complete agreement with the experimental outcomes. While the C–C bond formation involving the β-conjugated carbon of α-santonin derivative is more favorable than the C–O one, which is responsible for the ortho regioselectivity, the favorable electronic interactions taking place between the oxygen of the nitrile oxide and two axial hydrogen atoms of the α-santonin derivative are responsible for the syn diastereofacial selectivity.

Synthesis of novel 1,2,3-triazole-substituted tomentosins

A series of 1,2,3-triazole-containing tomentosin scaffolds was obtained from tomentosin 1. The synthesis involved a Michael addition of trimethylsilylazide on the α-methylene-γ-lactone function of the natural sesquiterpene lactone 1 to give the diastereoisomers 2 and 3, which were readily separated by column chromatography. These compounds underwent copper-catalyzed Huisgen 1,3-dipolar cycloaddition with various terminal alkynes to provide compounds 4a–h and 5a–h in good yields.