Synthesis of glycyrrhetinic acid derivatives for the treatment of metabolic diseases

Trojan-Horse Strategy Targeting the Gut-Liver Axis Modulates Gut Microbiome and Reshapes Microenvironment for Orthotopic Hepatocellular Carcinoma Therapy

Reversing the hepatic inflammatory and immunosuppressive microenvironment caused by gut microbiota-derived lipopolysaccharides (LPS), accumulating to the liver through the gut-liver axis, is crucial for suppressing hepatocellular carcinoma (HCC) and metastasis. However, synergistically manipulating LPS-induced inflammation and gut microbiota remains a daunting task. Herein, a Trojan-horse strategy is proposed using an oral dextran-carbenoxolone (DEX-CBX) conjugate, which combines prebiotic and glycyrrhetinic acid (GA) homologs, to targeted delivery GA to HCC through the gut-liver axis for simultaneous modulation of hepatic inflammation and gut microbiota. In the orthotopic HCC model, a 95-45% reduction in the relative abundances of LPS-associated microbiota is observed, especially Helicobacter, caused by DEX-CBX treatment over phosphate-buffered saline (PBS) treatment. Notably, a dramatic increase (37-fold over PBS) in the abundance of Akkermansia, which is known to strengthen systemic immune response, is detected. Furthermore, DEX-CBX significantly increased natural killer T cells (5.7-fold) and CD8+ T cells (3.9-fold) as well as decreased M2 macrophages (59% reduction) over PBS treatment, resulting in a tumor suppression rate of 85.4%. DEX-CBX is anticipated to offer a novel strategy to precisely modulate hepatic inflammation and the gut microbiota to address both the symptoms and root causes of LPS-induced immunosuppression in HCC.

Synthesis, modification and biological activity of 2,3-indoles of Glycyrrhetinic acid

The synthesis of 2,3-indoles of Glycyrrhetinic acid (GLA) and its methyl ester was carried out by the Fischer reaction. Reductive transformations of GLA methyl ester 2,3-indole 3a were carried out to obtain 11-deoxo- and 9,12-diene analogs. N-methylation of 2,3-indole 3a gave N-methyl-indole-11-oxo-18β-olean-12-en-30-oic acid. The antiulcer and anti-inflammatory activity of 2,3-indole 3a was studied in rats and mice. It was found, compound 3a exhibied a pronounced antiulcer activity in the indomethacin model of ulcers in rats and anti-inflammatory activity in the carrageenan model of acute edoema in mice, at a dose of 50 mg/kg. This is the first report of anti-ulcer and anti-inflammatory activities of 2,3-indolo-GLA derivatives.

A Classic Photochemical Approach Inducing an Unexpected Rearrangement: Exploring the Photoreactivity of Pentacyclic Triterpenic Acids

The discovery of new bioactivities is closely related to the generation of novel scaffolds, and in the past few years different strategies have been proposed to obtain unknown architectures from the manipulation of known compounds. In the present study, we exploited a vintage photochemical approach for the discovery of an unexpected pathway of reactivity related to Δ¹-3-oxo-pentacyclic triterpenic acids gaining access to a new class of natural-unnatural 5(10→1)abeo-pentacyclic triterpenic acids.

Rhodococcus rhodochrous IEGM 1360, an Effective Biocatalyst of C3 Oxidative Transformation of Oleanane Triterpenoids

The optimal conditions for C3 oxidative biotransformation of 1.0 g/L pentacyclic triterpenoids oleanolic (OA) and glycyrrhetinic (GA) acids were determined using the resting cells of Rhodococcus rhodochrous IEGM 1360 from the Regional Specialised Collection of Alkanotrophic Microorganisms. Resting cell suspensions (OD600 2.6, pH 8.0, and OD600 2.2, pH 6.0) showed the highest catalytic activity against OA and GA, resulting in the formation of 61 and 100% of their 3-oxo derivatives, respectively. Using phase contrast, atomic force, and confocal laser scanning microscopy, an adaptive response of rhodococci to the effects of OA and GA was revealed. In silico, the apoptotic activity of 3-oxo-OA and antioxidant activity of 3-oxo-GA have been assumed. In vitro, a pronounced antibacterial activity of 3-oxo-OA against Micrococcus luteus, Escherichia coli, Staphylococcus aureus, and Bacillus subtilis was shown. The absence of toxic effects of the above triterpenoids and their 3-oxo derivatives on aquatic objects and plants was demonstrated in silico and in vitro, respectively.

Supplementary Information

The online version contains supplementary material available at 10.1134/S0026261722603360.

Polymorphism of Butyl Ester of Oleanolic Acid—The Dominance of Dispersive Interactions over Electrostatic

Oleanolic (OA) and glycyrrhetinic acids (GE), as well as their derivatives, show a variety of pharmacological properties. Their crystal structures provide valuable information related to the assembly modes of these biologically active compounds. In the known-to-date crystals of OA esters, their 11-oxo derivatives, and GE ester crystals, triterpenes associate, forming different types of ribbons and layers whose construction is based mainly on van der Waals forces and weak C-H···O interactions. New crystal structures of 11-oxo OA methyl ester and the polymorph of OA butyl ester reveal an alternative aggregation mode. Supramolecular architectures consist of helical chains which are stabilized by hydrogen bonds of O-H···O type. It was found that two polymorphic forms of butyl OA ester (layered and helical) are related monotropically. In a structure of metastable form, O-H···O hydrogen bonds occur, while the thermodynamically preferred phase is governed mainly by van der Waals interactions. The intermolecular interaction energies calculated using CrystalExplorer, PIXEL, and Psi4 programs showed that even in motifs formed through O-H···O hydrogen bonds, the dispersive forces have a significant impact.

Small Structural Differences Govern the Carbonic Anhydrase II Inhibition Activity of Cytotoxic Triterpene Acetazolamide Conjugates

Acetylated triterpenoids betulin, oleanolic acid, ursolic acid, and glycyrrhetinic acid were converted into their succinyl-spacered acetazolamide conjugates. These conjugates were screened for their inhibitory activity onto carbonic anhydrase II and their cytotoxicity employing several human tumor cell lines and non-malignant fibroblasts. As a result, the best inhibitors were derived from betulin and glycyrrhetinic acid while those derived from ursolic or oleanolic acid were significantly weaker inhibitors but also of diminished cytotoxicity. A betulin-derived conjugate held a K_i = 0.129 μM and an EC₅₀ = 8.5 μM for human A375 melanoma cells.

Analysis of the network pharmacology and the structure-activity relationship of glycyrrhizic acid and glycyrrhetinic acid

Licorice, a herbal product derived from the root of Glycyrrhiza species, has been used as a sweetening agent and traditional herbal medicine for hundreds of years. Glycyrrhizic acid (GL) and glycyrrhetinic acid (GA) are the most important active ingredients in licorice. Both GL and GA have pharmacological effects against tumors, inflammation, viral infection, liver diseases, neurological diseases, and metabolic diseases. However, they also exhibit differences. KEGG analysis indicated that licorice is involved in neuroactive ligand‒receptor interactions, while 18β-GA is mostly involved in arrhythmogenic right ventricular cardiomyopathy. In this article, we comprehensively review the therapeutic potential of GL and GA by focusing on their pharmacological effects and working mechanisms. We systemically examine the structure-activity relationship of GL, GA and their isomers. Based on the various pharmacological activities of GL, GA and their isomers, we propose further development of structural derivatives of GA after chemical structure modification, with less cytotoxicity but higher targeting specificity. More research is needed on the clinical applications of licorice and its active ingredients.

Insights into isostructural and non-isostructural crystals of esters of oleanolic acid and its 11-oxo derivatives

Synthesis and structural characterization of new esters of oleanolic acid and its 11-oxo derivatives are reported. Compounds crystallize in four isostructural groups, each containing one to four structures. Single-crystal X-ray analysis revealed that molecules belonging to non-isostructural groups self-associate according to two schemes that describe also supramolecular architectures in crystals of glycyrrhetinic acid derivatives. Structural motifs arise as a result of van der Waals forces. Parameters introduced for the analysis of one- and two-dimensional assemblies allow the comparison of motifs in isostructural and non-isostructural crystals, including polymorphs, and a qualitative assessment of differences in molecular self-assembly. One-, two- or three-dimensional similarity has been confirmed by XPac calculations.

Preclinical Evidence for the Pharmacological Actions of Glycyrrhizic Acid: A Comprehensive Review

Glycyrrhiza glabra L. (Family: Fabaceae) is one of the important traditional medicinal plant used extensively in folk medicine. It is known for its ethnopharmacological value in curing a wide variety of ailments. Glycyrrhizin, an active compound of G. glabra, possesses anti-inflammatory activity due to which it is mostly used in traditional herbal medicine for the treatment and management of chronic diseases. The present review is focused extensively on the pharmacology, pharmacokinetics, toxicology, and potential effects of Glycyrrhizic Acid (GA). A thorough literature survey was conducted to identify various studies that reported on the GA on PubMed, Science Direct and Google Scholar.

Glycyrrhetinic acid derivatives as Zika virus inhibitors: Synthesis and antiviral activity in vitro

Zika virus (ZIKV) is an arbovirus of the Flaviviridae family (Flavivirus genus), causing serious neurological complications, such as Guillain-Barre Syndrome (GBS) in adults and fetal microcephaly. Licensed vaccines or specific antiviral agents against ZIKV do not currently exist. Therefore, the search and development of anti-ZIKV agents are particularly relevant and necessary. Glycyrrhetinic (3β-hydroxy-11-oxo-18βH-Olean-12-en-30-oic acid) (GA) 1 is one of the well-known pentacyclic triterpenoids isolated from licorice root (Glycyrrhiza glabra L., Gl. uralensis Fisher) (Leguminosae) possessing many biological features, including antiviral activity. This paper is devoted to the synthesis and studies of a number of nitrogen and sulfur-containing GA derivatives as ZIKV inhibitors. Sixteen GA and related triterpenoids (3β-hydroxy-18βH-Olean-12-en-30-oic acid and 3β-hydroxy-11-oxo-18βH-Olean-12(13),18(19)-dien-30-oic acid) derivatives were synthesized (amides, semi- and thiosemicarbazones, and 1,2,3-thiadiazoles) and antiviral activity against ZIKV was studied in vitro, including the inhibitory assays on cytopathic effect (CPE), viral protein synthesis, and replication stages. Four active compounds were found among GA derivatives tested, 13 (3-O-acetyl-30-aminopyridine GA), 16 (3-semicarbazone-30-butyl GA), 18 (1,2,3-thiadiazole-30-methyl GA), and 19 (1,2,3-thiadiazole-30-butyl GA) with IC₅₀ < 1 μM against ZIKV replication. These compounds had a stronger inhibitory activity on ZIKV-induced CPE and viral protein translation in infected cells as compared to derivatives of 11-desoxo-GA. The most active compound was amide 13 (IC₅₀ 0.13 μM, TI ˃ 384). Time-of-addition assays indicated that 1,2,3-thiadiazole ring is important for inhibiting viral entry stage (compounds 18 and 19), while the 30-butyl ester group influenced on post-entry stage (compound 19). The molecular docking analysis demonstrated that lead compounds 13 and 19 forms a hydrogen-bond interaction with the catalytic triad (His51-Asp75-Ser135) of ZIKV NS2B-NS3 protease. Therefore, the active GA derivatives are promising for developing new antiviral agents against ZIKV infection.

Efficient synthesis of piperazinyl amides of 18β-glycyrrhetinic acid

In the present study, a practical method to prepare piperazinyl amides of 18β-glycyrrhetinic acid was developed. Two main procedures for the construction of important intermediate 8 are discussed. One procedure involves the amidation of 1-Boc-piperazine with 3-acetyl-18β-glycyrrhetinic acid, prepared by the reaction of 18β-glycyrrhetinic acid with acetic anhydride without any solvent at 130 °C. The other procedure to prepare compound 8 involves the amidation of 18β-glycyrrhetinic acid followed by the esterification with acetic anhydride. Finally, compound 8 underwent N-Boc deprotection to prepare product 4. To ascertain the scope of the reaction, another C-3 ester derivative 17 was tested under the optimized reaction conditions. Furthermore, the reasons for the appearance of byproducts were elucidated. Crystallographic data of a selected piperazinyl amide is reported.

Synthesis and structure-activity relationship studies of water-soluble β-cyclodextrin-glycyrrhetinic acid conjugates as potential anti-influenza virus agents

Glycyrrhetinic acid (GA) is a major constituent of the herb Glycyrrhiza glabra, and many of its derivatives demonstrate a broad spectrum of antiviral activities. In the current study, 18 water-soluble β-cyclodextrin (CD)-GA conjugates, in which GA was covalently coupled to the primary face of β-CD using 1,2,3-triazole moiety along with varying lengths of linker, were synthesized via copper-catalyzed azide-alkyl cycloaddition reaction. Benefited from the attached β-CD moiety, all these conjugates showed lower hydrophobicity (AlogP) compared with their parent compound GA. With the exception of per-O-methylated β-CD-GA conjugate (35), all other conjugates showed no significant cytotoxicity to MDCK cells, and these conjugates were then screened against A/WSN/33 (H1N1) virus using the cytopathic effect assay. The preliminary results indicated that six conjugates showed promising antiviral activity, and the C-3 and C-30 of GA could tolerate some modifications. Our findings suggested that GA could be used as a lead compound for the development of potential anti-influenza virus agents.

Derivatization, molecular docking and in vitro acetylcholinesterase inhibitory activity of glycyrrhizin as a selective anti-Alzheimer agent

Acetylcholinesterase inhibitors (AChE-Is) increase both level and duration of action of acetylcholine (ACh); thus, alleviate symptoms of Alzheimer's disease (AD). Glycyrrhizin, is the main active compound in liquorice root. Its aglycone, glycyrrhetinic acid, has shown several beneficial pharmacological activities. This study reports the synthesis and screening of a series of glycyrrhetinic acid analogs as AChE-Is. Fourteen derivatives were prepared, of which five derivatives are recorded as new viz., 3-phenyl-carbamoyl-18β-glycyrrhetinic acid (J9), 3-acetyl-18β-glycyrrhetinic-30-anilinamide (J10), 3-acetyl-18β-glycyrrhetinic-30-ethanolamide (J11), 3-acetyl-18β-glycyrrhetinic-30-n-butylamide (J12) and 18β-glycyrrhetinic acid-30-prenyl ester (J14), in addition to nine known derivatives (J1-J8 & J13). Compounds J12, J11, J0 and J3 showed remarkable AChE-I activity with IC₅₀ values of 3.43, 5.39, 6.27 and 8.68 μM, respectively. These results are in full agreement with the docking study. The active compounds were non-cytotoxic to normal cells (WI-38).

Self-assembly modes of glycyrrhetinic acid esters in view of the crystal packing of related triterpene molecules

The crystal structures of three ester derivatives of glycyrrhetinic acid (GE) are reported. X-ray crystallography revealed that despite differences in the size of the ester substituents (ethyl, isopropyl and 2-morpholinoethyl) the scheme of molecular self-assembly is similar in all three cases but differs significantly from that observed in other known GE esters. According to our analysis, the two basic patterns of self-assembly of GE esters observed in their unsolvated crystals correspond to two distinct orientations of the ester groups relative to the triterpene backbone. Moreover, comparison of the self-assembly modes of GE esters in their unsolvated forms with the supramolecular organization of GE and carbenoxolone in their solvated crystals revealed that ester substituents replace solvent molecules hydrogen bonded to the COOH group at the triterpene skeleton, resulting in similar packing arrangements of these compounds.

18β-Glycyrrhetinic Acid Derivatives Possessing a Trihydroxylated A Ring Are Potent Gram-Positive Antibacterial Agents

The oleanane-type triterpene 18β-glycyrrhetinic acid (1) was modified chemically through the introduction of a trihydroxylated A ring and an ester moiety at C-20 to enhance its antibacterial activity. Compounds 22, 23, 25, 28, 29, 31, and 32 showed more potent inhibitory activity against Streptomyces scabies than the positive control, streptomycin. Additionally, the inhibitory activity of the most potent compound, 29, against Bacillus subtilis, Staphylococcus aureus, and methicillin-resistant Staphylococcus aureus was greater than that of the positive controls. The antibacterial mode of action of the active derivatives involved the regulation of the expression of genes associated with peptidoglycans, the respiratory metabolism, and the inherent virulence factors found in bacteria, as determined through a quantitative real-time reverse transcriptase PCR assay.

The licorice pentacyclic triterpenoid component 18β-glycyrrhetinic acid enhances the activity of antibiotics against strains of methicillin-resistant Staphylococcus aureus

This study aimed to identify compounds that enhance the activity of current antibiotics against multidrug-resistant bacteria. Screening of a 350+ compound proprietary small molecules library revealed that the Glycyrrhiza glabra (licorice)-derived triterpenoid 18β-glycyrrhetinic acid (18β-GA) potentiated the antibacterial activity of certain antibiotics against Staphylococcus aureus. Here, we evaluated the ability of pentacyclic triterpenoids to potentiate the activity of antibiotics against strains of methicillin-resistant S. aureus (MRSA). Checkerboard assays were used to assess the minimum inhibitory concentration (MIC) of tobramycin and ten pentacyclic triterpenoids against S. aureus. The effect of 18β-GA on the MIC of different antibiotics against MRSA was also determined in an in vitro airway MRSA infection model. 18β-GA enhanced the bactericidal activity of the aminoglycosides tobramycin, gentamicin and amikacin, and of polymyxin B against two MRSA strains, reducing the MIC of these antibiotics 32-64-fold [fractional inhibitory concentration index (FICI) of 0.12-0.13]. Other β-amyrin triterpenoids and α-amyrin triterpenoids did not exert such synergistic effects. 18β-GA did not enhance the activity of antibiotics from other structural classes against the MRSA strains. In an air-exposed airway epithelial cell culture, 18β-GA enhanced the bactericidal activity of tobramycin and polymyxin B against the MRSA strain. These data demonstrate the potential of 18β-GA to synergise with certain types of antibiotics to eliminate strains of MRSA.

Solid-state supramolecular architecture of carbenoxolone – comparative studies with glycyrrhetinic and glycyrrhizic acids

Carbenoxolone (CBXH2), a pharmaceutically relevant derivative of glycyrrhetinic acid, was studied by X-ray crystallography. The crystal structures of its unsolvated form, propionic acid and dimethoxyethane solvates and a solvated cocrystal of the free acid with its monobasic sodium salt CBXH2·CBXHNa·(butan-2-one)2·2H2O reveal that the recurring motif of supramolecular architecture in all crystal forms is a one-dimensional ribbon with closely packed triterpene fragments. It does not result from strong specific interactions but solely from van der Waals interactions. The ribbons are further arranged into diverse layer-type aggregates with a hydrophobic interior (triterpene skeletons) and hydrophilic surfaces covered with carboxylic/carboxylate groups. Solvent molecules included at the interface between the layers influence hydrogen-bonding interactions between the carbenoxolone molecules and organization of the ribbons within the layer. Comparison of crystal structures of carbenoxolone, glycyrrhizic acid and its aglycone-glycyrrhetinic acid have shown the impact of the size and hydrophilic character of the substituent at the triterpene C3 atom on the supramolecular architecture of these three closely related molecules.

Shieldable tumor targeting based on pH responsive self-assembly/disassembly of gold nanoparticles

A new approach to shield/deshield ligands for controllable tumor targeting was reported, which was based on amphiphilic self-assembly and disassembly of gold nanoparticles (Au NPs). Thanks to the excellent pH response of the system, glycyrrhetinic acid (GA) ligands can be buried inside the Au NPs' assembly at normal tissue pH (pH 7.4), while exposed when the nanostructure is disassembled at tumor extracellular pH (pHe 6.8). Hydrophobic GA molecules not only acted as ligands targeting tumor cells but also provided the major interparticle attractive force for Au NPs' assembling. An ordered assembly of Au NPs with regular shape, proper size and ultrasharp pH sensitivity (ΔpH ∼ 0.2) was achieved by fine-tuning of materials modified on Au NPs. Mechanism studies for assembly and disassembly of Au NPs indicated the possibility of a GA shield when the assembly formed, which was further demonstrated by bovine serum albumin absorption and cellular uptake. The assembly/disassembly process was reversible within extrinsic pH changes, which provides a perspective for reversible tumor targeting.

Involvement of BID translocation in glycyrrhetinic acid and 11-deoxy glycyrrhetinic acid-induced attenuation of gastric cancer growth

Glycyrrhetinic acid (GA), the main chemical constituents of licorice, has shown remarkable anticancer activity. However, the side effects limit its widespread use. 11-DOGA is produced through reduction of GA 11-carbonyl to 11-hydroxyl to reduce its side effects, although its anticancer activities are largely unknown. Here, we report that the functional mechanisms of GA and 11-DOGA in gastric cancers, as well as the comparison between these two drugs' pharmacological potential. Firstly, we found that GA and 11-DOGA significantly inhibits the viabilities of gastric cancer cells in dose- and time-dependent manners. Both GA and 11-DOGA induce gastric cancer cells apoptosis and cell cycle arrest in G2 phase by upregulation of p21 and downregulation of cdc2 and cyclin B1. Further studies show that GA and 11-DOGA-induced apoptosis in gastric cancer cells is associated with BID translocation from nucleus to mitochondria. Moreover, GA and 11-DOGA could effectively inhibit tumor formation of gastric cancer cells in nude mice. Comparing with 11-DOGA, GA presents higher toxicity toward gastric cancer cells both in vivo and in vitro. Thus, the elucidation of the functional mechanisms of GA and 11-DOGA-induced attenuation of gastric cancer growth suggests a possible therapeutic role of GA and its derivatives.

Discovery of a potential anti-inflammatory agent: 3-oxo-29-noroleana-1,9(11),12-trien-2,20-dicarbonitrile

Fifteen novel derivatives of glycyrrhetinic acid (GA) were synthesized and evaluated for anti-inflammatory activities. It was found that the introduction of 1-en-3-one and 9(11),12-diene and 2,20-dinitrile functionalities into the scaffold of GA led to the discovery of potent compound 19 for inhibition of LPS-induced NO production. Furthermore, 19 effectively inhibited the protein and mRNA expression of inducible NO synthase (iNOS) and the mRNA expression of TNF-α, IL-6, and IL-1β in LPS-stimulated RAW 264.7 macrophages. Mechanistically, 19 exerted inhibitory effects on the activation of the three main MAPKs and phosphorylation and degradation of IκB-α, as well as the ratio of nuclear/cytosolic content of p65. Importantly, 19 significantly decreased the mortality rate in the mouse model of LPS-induced sepsis shock. It is noteworthy that inhibitory effect of 19 on NO production was not blocked by the glucocorticoid receptor antagonist mifepristone, indicating that it does not act through the glucocorticoid receptor.

Synthesis and antiviral activities of spacer-linked 1-thioglucuronide analogues of glycyrrhizin

The influenza virus infection remains a significant threat to public health and the increase of antiviral resistance to available drugs generates an urgent need for new antiviral compounds. Starting from the natural, antivirally active compound glycyrrhizin, spacer-bridged derivatives were generated with improved antiviral activity against the influenza A virus infection. Simplified analogues of the triterpene saponin glycyrrhizin containing 1-thio-β-D-glucuronic acid residues have been prepared in good yields by alkylation of 3-amino and 3-thio derivatives of glycyrrhetinic acid with a 2-iodoethyl 1-thio-β-D-glucopyranosiduronate derivative. The spacer-connected 3-amino derivatives were further transformed into N-acetylated and N-succinylated derivatives. The deprotected compounds containing these carboxylic acid appendices mimic the glycon part of glycyrrhizin as well as the hemisuccinate derivative of glycyrrhetinic acid, carbenoxolone. Antiviral activities of the compounds were determined in a biological test based on influenza A virus-infected cells, wherein the 3-(2-thioethyl)-N-acetylamino- and 3-(2-thioethyl)-thio-linked glucuronide derivatives were effective inhibitors with IC₅₀ values as low as 54 µM.

(3β,18β,20β)-N-Eth-oxy-carbonyl-methyl-3-nitrato-11-oxoolean-12-ene-29-carboxamide methanol monosolvate

The title compound, C(34)H(52)N(2)O(7)·CH(4)O, is the methanol solvate of a difunctionalized derivative of the therapeutic agent 18β-glycyrrhetinic acid, a penta-cyclic triterpene. The five six-membered rings of the glycyrrhetinic acid moiety show normal geometries, with four rings in chair conformations and the unsaturated ring in a half-chair conformation. This moiety is substituted by a nitrate ester group and an O-ethyl-glycine group. In the crystal, the nonsolvent mol-ecules are packed parallel to (010) in a herringbone fashion with the nitrato, ethyl-glycine and methanol-O atom being proximate. The methanol solvent mol-ecule is anchored via a donated O-H⋯O(ac-yl) and an accepted N-H⋯O hydrogen bond, giving rise to infinite zigzag chains of hydrogen bonds parallel to [100]. Two weak intermolecular C-H⋯O interactions to the methanol and to an acyl oxygen establish links along [100] and [010], respectively.

Propargylaminyl 3α-hydroxy-11-oxo-18β-olean-12-en-29-oate

The title compound, C₃₃H₄₉NO₃, is the propargyl­amide of 18β-glycyrrhetinic acid, a penta­cyclic triterpenoid of inter­est as a therapeutic agent. The five six-membered rings of the glycyrrhetinic acid moiety show normal geometries, with four rings in chair conformations and the unsaturated ring C in a half-chair conformation. In the crystal, the terminal N-propargylcarboxamide group has remarkable structural effects on weak hydrogen-bond-like inter­actions. Particularly noteworthy are an inter­molecular O—H⋯π inter­action accepted side-on by the terminal alkyne group [O⋯C = 3.097 (2) and 3.356 (2) Å] and a short inter­molecular C—H⋯O inter­action [C⋯O = 3.115 (2) Å] donated by the alkyne C—H group. An N—H⋯O [N⋯O = 3.251 (2) Å] and a C_alkyl—H⋯O [C⋯O = 3.254 (2) Å] interaction complement the crystal structure.

Characterization of activity and binding mode of glycyrrhetinic acid derivatives inhibiting 11β-hydroxysteroid dehydrogenase type 2

Modulation of intracellular glucocorticoid availability is considered as a promising strategy to treat glucocorticoid-dependent diseases. 18β-Glycyrrhetinic acid (GA), the biologically active triterpenoid metabolite of glycyrrhizin, which is contained in the roots and rhizomes of licorice (Glycyrrhiza spp.), represents a well-known but non-selective inhibitor of 11β-hydroxysteroid dehydrogenases (11β-HSDs). However, to assess the physiological functions of the respective enzymes and for potential therapeutic applications selective inhibitors are needed. In the present study, we applied bioassays and 3D-structure modeling to characterize nine 11β-HSD1 and fifteen 11β-HSD2 inhibiting GA derivatives. Comparison of the GA derivatives in assays using cell lysates revealed that modifications at the 3-hydroxyl and/or the carboxyl led to highly selective and potent 11β-HSD2 inhibitors. The data generated significantly extends our knowledge on structure-activity relationship of GA derivatives as 11β-HSD inhibitors. Using recombinant enzymes we found also potent inhibition of mouse 11β-HSD2, despite significant species-specific differences. The selected GA derivatives potently inhibited 11β-HSD2 in intact SW-620 colon cancer cells, although the rank order of inhibitory potential differed from that obtained in cell lysates. The biological activity of compounds was further demonstrated in glucocorticoid receptor (GR) transactivation assays in cells coexpressing GR and 11β-HSD1 or 11β-HSD2. 3D-structure modeling provides an explanation for the differences in the selectivity and activity of the GA derivatives investigated. The most potent and selective 11β-HSD2 inhibitors should prove useful as mechanistic tools for further anti-inflammatory and anti-cancer in vitro and in vivo studies. Article from the Special issue on Targeted Inhibitors.

(+)-Methyl 3β-acet-oxy-13-carb-oxy-19-hy-droxy-11-oxo-C-norolean-18-en-30-oate γ-lactone

The title compound, C(33)H(46)O(7), is an unusual oxydation product of the therapeutic agent glycyrrhetinic acid that has, in comparison to the latter, a distinctly altered triterpene structure with one five- and four six-membered carbocycles complemented by a γ-lactone ring with a spiro-junction and a ring double bond. The junction between the five-membered ring C, a cyclo-penta-none ring, and the six-membered ring D, previously in question, was found to be cis, confirming earlier structure assignments based solely on chemical transformations. In the solid state, the compound exhibits five intra- and four inter-molecular C-H⋯O inter-actions with H⋯O distances less than or equal to 2.70 Å and C-H⋯O greater than 100°.