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-ß-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-ß-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 IC(50) values as low as 54 µM.

Synthesis of new glycyrrhetinic acid derived ring A azepanone, 29-urea and 29-hydroxamic acid derivatives as selective 11ß-hydroxysteroid dehydrogenase 2 inhibitors.

Glycyrrhetinic acid, the metabolite of the natural product glycyrrhizin, is a well known nonselective inhibitor of 11ß-hydroxysteroid dehydrogenase (11ß-HSD) type 1 and type 2. Whereas inhibition of 11ß-HSD1 is currently under consideration for treatment of metabolic diseases, such as obesity and diabetes, 11ß-HSD2 inhibitors may find therapeutic applications in chronic inflammatory diseases and certain forms of cancer. Recently, we published a series of hydroxamic acid derivatives of glycyrrhetinic acid showing high selectivity for 11ß-HSD2. The most potent and selective compound is active against human 11ß-HSD2 in the low nanomolar range with a 350-fold selectivity over human 11ß-HSD1. Starting from the lead compounds glycyrrhetinic acid and the hydroxamic acid derivatives, novel triterpene type derivatives were synthesized and analyzed for their biological activity against overexpressed human 11ß-HSD1 and 11ß-HSD2 in cell lysates. Here we describe novel 29-urea- and 29-hydroxamic acid derivatives of glycyrrhetinic acid as well as derivatives with the Beckman rearrangement of the 3-oxime to a seven-membered ring, and the rearrangement of the C-ring from 11-keto-12-ene to 12-keto-9(11)-ene. The combination of modifications on different positions led to compounds comprising further improved selective inhibition of 11ß-HSD2 in the lower nanomolar range with up to 3600-fold selectivity.

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

Modulation of intracellular glucocorticoid availability is considered as a promising strategy to treat glucocorticoid-dependent diseases. 18ß-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 11ß-hydroxysteroid dehydrogenases (11ß-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 11ß-HSD1 and fifteen 11ß-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 11ß-HSD2 inhibitors. The data generated significantly extends our knowledge on structure-activity relationship of GA derivatives as 11ß-HSD inhibitors. Using recombinant enzymes we found also potent inhibition of mouse 11ß-HSD2, despite significant species-specific differences. The selected GA derivatives potently inhibited 11ß-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 11ß-HSD1 or 11ß-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 11ß-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.

Synthesis of novel 3-amino and 29-hydroxamic acid derivatives of glycyrrhetinic acid as selective 11ß-hydroxysteroid dehydrogenase 2 inhibitors.

Glycyrrhetinic acid, the metabolite of the natural product glycyrrhizin, is a well known nonselective inhibitor of 11ß-hydroxysteroid dehydrogenase (11ß-HSD) type 1 and type 2. Whereas inhibition of 11ß-HSD1 is currently under consideration for treatment of metabolic diseases, such as obesity and diabetes, 11ß-HSD2 inhibitors may find therapeutic applications in chronic inflammatory diseases and certain forms of cancer. So far, no selective 11ß-HSD2 inhibitor has been developed and neither animal studies nor clinical trials have been reported based on 11ß-HSD2 inhibition. Starting from the lead compound glycyrrhetinic acid, novel triterpene type derivatives were synthesized and analyzed for their biological activity against overexpressed human 11ß-HSD1 and 11ß-HSD2 in cell lysates. Several hydroxamic acid derivatives showed high selectivity for 11ß-HSD2. The most potent and selective compound is active against human 11ß-HSD2 in the low nanomolar range with a 350-fold selectivity over human 11ß-HSD1.

Synthesis of glycyrrhetinic acid derivatives for the treatment of metabolic diseases.

The effect of glycyrrhetinic acid (GA) and GA-derivatives towards 11beta-hydroxysteroid dehydrogenase (11beta-HSD) was investigated. Novel compounds with modifications at positions C-3, C-11 and C-29 of the GA skeleton were prepared. Single crystal X-ray diffraction data of selected substances are reported and discussed.

Efficient synthesis of glycyrrhetinic acid glycoside/glucuronide derivatives using silver zeolite as promoter.

3-O-Glycopyranosides of glycyrrhetinic acid have been synthesized in good to high yields and excellent stereoselectivity using glycosyl bromide donors and silver zeolite as promoter. In addition to the preparation of glycosides containing beta-linked glucosyl, 2-deoxy-2-trichloroacetamido-glucosyl, galactosyl, cellobiosyl and lactosyl residues, also the deactivated acetylated methyl glucopyranosyluronate bromide donor could be coupled to triterpene aglycon ester derivatives in good yields. The ester protecting group located at C-30 of the oleanolic acid scaffold exerted an influence on the overall yield, with the methylester-protected glycosyl acceptor giving better yields compared to the allyl, benzyl as well as diphenylmethyl ester aglycon. The acetyl-protected glucuronides were differently deblocked in high yields via Zemplén deacetylation or via hydrogenolysis followed by Zemplén deacetylation, and alkaline hydrolysis, respectively, to allow for a selective liberation of the ester groups from either the glucuronide or the glycyrrhetinic acid unit, respectively. The target glycosides/glucuronides serve as probes for pharmaceutical studies aimed at defining structure-activity relationships of glycoside/glucuronide triterpenes.

Selective inhibition of 11beta-hydroxysteroid dehydrogenase 1 by 18alpha-glycyrrhetinic acid but not 18beta-glycyrrhetinic acid.

Elevated cortisol concentrations have been associated with metabolic diseases such as diabetes type 2 and obesity. 11beta-hydroxysteroid dehydrogenase (11beta-HSD) type 1, catalyzing the conversion of inactive 11-ketoglucocorticoids into their active 11beta-hydroxy forms, plays an important role in the regulation of cortisol levels within specific tissues. The selective inhibition of 11beta-HSD1 is currently considered as promising therapeutic strategy for the treatment of metabolic diseases. In recent years, natural compound-derived drug design has gained considerable interest. 18beta-glycyrrhetinic acid (GA), a metabolite of the natural product glycyrrhizin, is not selective and inhibits both 11beta-HSD1 and 11beta-HSD2. Here, we compare the biological activity of 18beta-GA and its diastereomer 18alpha-GA against the two enzymes in lysates of transfected HEK-293 cells and show that 18alpha-GA selectively inhibits 11beta-HSD1 but not 11beta-HSD2. This is in contrast to 18beta-GA, which preferentially inhibits 11beta-HSD2. Using a pharmacophore model based on the crystal structure of the GA-derivative carbenoxolone in complex with human 11beta-HSD1, we provide an explanation for the differences in the activities of 18alpha-GA and 18beta-GA. This model will be used to design novel selective derivatives of GA.