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.

(3ß,18ß,20ß)-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 18ß-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.

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.

Propargylaminyl 3α-hy-droxy-11-oxo-18ß-olean-12-en-29-oate.

The title compound, C(33)H(49)NO(3), is the propargyl-amide of 18ß-glycyrrhetinic acid, a penta-cyclic triterpenoid of inter-est 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 inter-actions. Particularly noteworthy are an inter-molecular O-H⋯π inter-action accepted side-on by the terminal alkyne group [O⋯C = 3.097 (2) and 3.356 (2) Å] and a short inter-molecular C-H⋯O inter-action [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.

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.

NXO building blocks for backbone modification of peptides and preparation of pseudopeptides.

The design and synthesis of novel building blocks for peptide modification, termed "NXO", is reported. We describe the utility of these building blocks to prepare new pseudo- and oligopeptides and demonstrate the efficient assembly of modified tripeptides using both conventional liquid phase peptide synthesis and solid supported synthesis. Pertaining to the study of NXO in peptide mimicry, the structure of NXO-incorporating tripeptide beta-strand mimics was investigated in the N(L)AlaO incorporating beta-sheet model compound 13. Evidenced by spectroscopy and computation, 13 selectively adopts a beta-structure in chloroform and characteristically samples the NXO-modified backbone site in the core beta-sheet region. ROESY (HNMR) and molecular dynamics data suggest that when disrupting the cross-strand hydrogen-bonding pattern by switching the solvent from CDCl(3) to d(3)-MeOH, the main conformation with peptide and NXO-peptide backbones similar to that in root mean square deviation of corresponding backbone atoms (rmsd) is preserved.

(+)-Methyl 3ß-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 Šand C-H⋯O greater than 100°.

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.

Memogain is a galantamine pro-drug having dramatically reduced adverse effects and enhanced efficacy.

Memogain (Gln-1062) is an inactive pro-drug of galantamine, the latter being a plant alkaloid approved for the treatment of mild to moderate Alzheimer's disease. Memogain has more than 15-fold higher bioavailability in the brain than the same doses of galantamine. In the brain, Memogain is enzymatically cleaved to galantamine, thereby regaining its pharmacological activity as a cholinergic enhancer. In animal models of drug-induced amnesia, Memogain produced several fold larger cognitive improvement than the same doses of galantamine, without exhibiting any significant levels of gastrointestinal side effects that are typical for the unmodified drug and other inhibitors of cholinesterases, such as donepezil and rivastigmin. In the ferret, dramatically reduced emetic and behavioral responses were observed when Memogain was administered instead of galantamine. Based on these and other preclinical data, Memogain may represent an advantageous drug treatment for Alzheimer's disease, combining much lesser gastrointestinal side effects and considerably higher potency in enhancing cognition, as compared to presently available drugs.

Probing Torpedo californica acetylcholinesterase catalytic gorge with two novel bis-functional galanthamine derivatives.

N-Piperidinopropyl-galanthamine (2) and N-saccharinohexyl-galanthamine (3) were used to investigate interaction sites along the active site gorge of Torpedo californica actylcholinesterase (TcAChE). The crystal structure of TcAChE-2 solved at 2.3 A showed that the N-piperidinopropyl group in 2 is not stretched along the gorge but is folded over the galanthamine moiety. This result was unexpected because the three carbon alkyl chain is just long enough for the bulky piperidine group to be placed above the bottleneck (Tyr121, Phe330) midway down the gorge. The crystal structure of TcAChE-3 at 2.2 A confirmed that a dual interaction with the sites at the bottom, and at the entrance of the gorge, enhances inhibitory activity: a chain of six carbon atoms has, in this class of derivatives, the correct length for optimal interactions with the peripheral anionic site (PAS).

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.

Improved synthesis of substituted 6,7-dihydroxy-4-quinazolineamines: tandutinib, erlotinib and gefitinib.

The synthesis of three substituted 6,7-dihydroxy-4-quinazolineamines: tandutinib (1), erlotinib (2) and gefitinib (3) in improved yields is reported. The intermediates were characterized by NMR and the purities determined by HPLC.