Circular dichroism as a reliable tool for anomeric assignment of glycosyl-2-phenyl-2H-1,2,3-triazole C-nucleoside analogs. A rule for prediction of their anomeric configuration

The circular dichroism (CD) of a series of acyclic C-nucleoside analogs; 4-(pentahydroxypentyl-1-yl)-2-phenyl-2H-1,2,3-triazoles [1-5] and 4-(D-glycero-D-gulo)-2-phenyl-2H-1,2,3-triazole 6, are reported. A correlation between the sign of the Cotton effect at the maximal UV absorption and the absolute configuration of the carbon atom alpha- to the triazole base moiety is reported. The CD of anomeric 4-(alpha,beta-D-arabinofuranosyl)- and 4-(alpha,beta-D-arabinopyranosyl)-2-phenyl-2H-1,2,3-triazole C-nucleosides are reported. The assignment of the anomeric configuration of C-glycosyl-2-phenyl-2H-1,2,3-triazoles from their CD spectra was found to be a simple method that relies on comparison of the sign of the Cotton effect at the maximal UV absorption and the absolute configuration of the anomeric carbon atom. A correlation between the anomeric configuration and the sign of the Cotton effect at the maximal UV absorption is deduced and generalized as a rule for prediction of the anomeric configuration of C-glycosyl-2-phenyl-2H-1,2,3-triazoles. Nuclear Overhauser effect and 13C NMR spectra supported the CD assignment rule.     

Acid-catalyzed dehydrative cyclization of 4-(D-galacto -pentitol-1-yl)-2-phenyl-2H-1,2,3-triazole. synthesis and anomeric configuration of D-lyxo-C-nucleoside analogs

Dehydration of 4-(D-galacto-pentitol-1-yl)-2-phenyl-2H-1,2,3-triazole with 20% methanolic sulfuric acid afforded the anomeric pairs of nucleosides, 4-(alpha-D-lyxopyranosyl)-2-phenyl-2H-1,2,3-triazole (major component) and its beta-anomer, as well as 4-(alpha-D-lyxofuranosyl)-2H-1,2,3-triazole and its beta-anomer. The four anomeric C-nucleosides were separated by chromatography, and their structure and anomeric configuration were determined by periodate oxidation, acylation, and NMR spectroscopy as well as mass spectrometry. The anomeric assignment from optical rotation was not in agreement with final structure assignment and represented a violation of the Hudson isorotation rules. NOE studies and X-ray diffraction measurements confirmed the anomeric configuration.     

Benzimidazole 2'-isonucleosides: design, synthesis, and antiviral activity of 2-substituted-5,6-dichlorobenzimidazole 2'-isonucleosides

2,5,6-Trihalogenated benzimidazole-beta-D-ribofuranosyl nucleosides and 2-substituted amino-5,6-dichlorobenzimidazole-beta-L-ribofuranosyl nucleosides are potent and selective inhibitors of human cytomegalovirus (HCMV). The D-ribofuranosyl analogs are metabolized rapidly in vivo rendering them unsuitable as drug candidates. The primary source of instability is thought to be the anomeric bond. The synthesis of a series of chemically stable benzimidazole-2'-isonucleosides is presented. The synthetic schemes employed are based on nucleophilic displacements of a 2'-tosylate from carbohydrate intermediates with 2-bromo-5,6-dichlorobenzidazole. 2-Bromo and 2-isopropyl amino analogs with 3'- and 5'-oxo and deoxy substitutions were prepared. The benzimidazole-2-'isonucleosides presented here demonstrated reduced activity against HCMV when compared to other D-ribofuranosyl benzimidazole analogs. In addition, they were not found to be inhibitors of HIV.     

Synthesis of pyridazine and thiazole analogs as SGLT2 inhibitors

With anticipation of the improvement in biological aspects in our SGLT2 program, novel pyridazinyl and thiazolyl analogs were designed and efficiently synthesized. The installation of the pyridazine ring at the anomeric carbon of d-glucopyranose was carried out in a stereoselective fashion. On the other hand, a series of thiazolyl analogs was also synthesized through a coupling reaction between perbenzyl gluconolactone 9 and 2-lithiothiazole. Biological activities of the compounds thus prepared were evaluated by the in vitro SGLT2 inhibition assay. Considering assay results, the novel benzylpyridazinyl and benzylthiazolyl analogs, disclosed in this article, could be a quick reference to prospective SGLT2 inhibitors useful for pharmacotherapy.     

CD and NMR assignment of the anomeric configuration of 4-(5-deoxy-α,β-l-arabinofuranosyl)-2-phenyl-2H-1,2,3-triazole C-nucleoside analogs

Acid-catalyzed dehydrative cyclization of 5-deoxy-l-manno-pentitol-1-yl)-2-heptulose bisphenylhydrazone and subsequent reflux with copper sulfate gave an anomeric mixture of 4-(5-deoxy-α,β-l-arabinofuranosyl)-2-phenyl-2H-1,2,3-triazole C-nucleoside analogs. The mixture was separated by chromatography, and the anomeric compositions configurations of the components were determined by CD, NMR, mass spectroscopy, and acylation.     

High-performance liquid chromatographic enantioseparation of 1-(aminoalkyl)-2-naphthol analogs on polysaccharide-based chiral stationary phases

The enantiomers of various 1-(alpha-aminobenzyl)-2-naphthol and 1-(aminoalkyl)-2-naphthol analogs were separated on cellulose-tris-3,5-dimethylphenyl carbamate-based chiral stationary phases (Chiralcel OD-H and Chiralcel OD-RH), using n-hexane/2-propanol/diethylamine or phosphate buffer/organic modifier mobile phases. The 3,5-dimethylphenyl carbamoylated cellulose columns were effective in both normal and rev ersed-phase modes. The effects of the mobile phase composition, the pH, the buffer concentration, and the structures of the substituents on the 2-naphthol on the enantioseparations were studied. The absolute configuration and elution sequence were determined for 1-(1-amino-2-methylpropyl)-2-naphthol: the elution sequence was S < R.     

Studies on epimeric D-xylo-and D-lyxo-tetritol-1-yl-2-phenyl-2H-1,2,3-triazoles. Synthesis and anomeric configuration of 4-(alpha-and beta-D-threofuranosyl)-2-phenyl-2H-1,2,3-triazole C-nucleoside analogs

Treatment of 4-(D-xylo-tetritol-1-yl)-2-phenyl-2H-1,2,3-triazole (1) with one mole equivalent of tosyl chloride in pyridine solution, afforded the C-nucleoside analog; 4-(beta-D-threofuranosyl)-2-phenyl-2H-1,2,3-triazole (2) in 55% yield, as well as the byproduct 4-(4-chloro-4-deoxy-D-xylo-tetritol-1-yl)-2-phenyl-2H-1,2,3-triazo le (4). Treatment of the epimeric 4-(D-lyxo-tetritol-1-yl)-2-phenyl-2H-1,2,3-triazole (6) with tosyl chloride in pyridine solution afforded the anomeric C-nucleoside analog; 4-(alpha-D-threofuranosyl)-2-phenyl-2H-1,2,3-triazole (7) in 29% yield, as well as the byproduct 4-(4-chloro-4-deoxy-D-lyxo-tetritol-1-yl)-2-phenyl-2H-1,2,3- triazole (9). Similar treatment of 1 and 6 with trifluoromethanesulfonyl chloride in pyridine solution afforded 2 and 7, respectively. The structure and anomeric configuration of these compounds were determined by acetylation, NMR, NOE, and circular dichroism spectroscopy, as well as mass spectrometry.     

2-(Aminomethyl)-2-decarboxyprostaglandin F2 alpha type analogs

The 2-(aminomethyl)-2-decarboxy analogs of prostaglandin F2 alpha (PGF2 alpha), (15S)-15-methyl-PGF2 alpha, 16-phenoxy-omega-tetranor-PGF2 alpha and 16,16-dimethyl-PGF2 alpha were synthesized. The amino analogs closely resemble the parent PGF2 alpha compounds as antifertility agents in the hamster.     

Synthesis and antimetabolite properties of 5-substituted 2'-deoxyuridines. Anomeric 5-(2-aminohexafluoroprop-2-yl)- and 5-(2-trifluoroacetylaminohexafluoroprop-2-yl)-2'-deoxyuridine

Alkylation of 2,4-bis-O-(trimethylsilyl)uracil with hexafluoroacetone trifluoroacetylimine gave 5-(2-trifluoroacelylaminohexafluoroprop-2-yl)uracil, which was transformed by alkaline hydrolysis to 5-(2-aminohexafluoroprop-2-yl)uracil. The latter was glycosytated with 2-deoxy-3,5-di-O-p-toluoyl-alpha-D-ribofyranosyl chloride by means of various modifications of the silyl method leading to the predominant formation of beta-deoxynucleoside; after deacylation 1-(2-deoxy-beta-D-ribofuranosyl)-5-(2-aminohexafluoroprop-2-yl)ura cil was obtained. Interaction of silylated 5-(2-trifluoroacetylaminohexafluoroprop-2-yl)uracil with acylgalogenose gave anomeric O-substitutet deoxynucleosides, which were deblocked to give 5-(2-trifluoroacetylaminohexafluoroprop-2-yl)-2'-deoxyuridine and corresponding alpha-anomer. Alkaline hydrolysis of N-trifluoroacetyl group in both individual anomers produced 1-(2-deoxy-alpha-D-ribofuranosyl)-5-(2-aminohexafluoroprop-2-yl)ur acil and the abovementioned beta-anomer. Of all compounds synthesised only 1-(2-deoxy-beta-D-ribofuranosyl)-5-(2-aminohexafluoroprop-2-yl)ura cil has a moderate inhibitory effect on replication of vaccinia virus in vitro.     

Studies on anhydro-osazones. Structure and anomeric configuration of the 3,6-anhydro-osazone derivatives obtained from D-galacto-2-heptulose phenylosazone

Dehydration of D-galacto-2-heptulose phenylosazone with methanolic sulfuric acid afforded two 3,6-anhydro-osazone derivatives (2 and 3). Compound 2 was obtained as the preponderant isomer, without inversion at C-1 (C-3 of the starting osazone), and 3 was obtained with inversion. The anomeric configurations of 2 and 3 were determined by n.m.r. spectroscopy. Refluxing of 2 and 3 with copper sulfate afforded two C-nucleoside analogs, namely, 4-β- and 4-α- D-lyxofuranosyl-2-phenyl-1,2,3-triazole, 4 and 5, respectively. The anomeric configurations of 4 and 5 were determined by n.m.r and c.d. spectroscopy. Acetylation of 4 and 5 afforded the tri-O-acetyl derivatives. The mass spectra of these compounds were discussed.     

Evaluation of 5-[1-(2-halo(or nitro)ethoxy-2-iodoethyl)]-2'-deoxyuridines as inhibitors of herpes simplex virus

A series of 5-[1-(2-haloethyl(or nitro)ethoxy-2-iodoethyl)]-2'-deoxyuridines (3-7) and related uracil analogs (9-10) were prepared using 5-vinyl-2-deoxyuridine (2) and 5-vinyl uracil (8) as starting materials. The regiospecific reaction of 2 and 8 with iodine monochloride and an alcohol provided the target compounds 3-10. These analogs were evaluated in vitro for inhibitory activity against thymidine-kinase (TK) positive and negative strains of herpes simplex virus type-1. The compounds 3-10 were either weak or non-inhibitory to HSV-1 replication. All compounds investigated exhibited low host cell cytotoxicity.     

Structure and anomeric configuration of the C-nucleoside analogs obtained by dehydration of 7-deoxy-l-manno-2-heptulose phenylosazone

Dehydration of 7-deoxy-l-manno-2-heptulose phenylosazone with methanolic sulfuric acid afforded two 3,6-anhydro-osazone derivatives (2 and 3). Refluxing the anhydro-osazones with copper sulfate gave two C-nucleoside analogs, namely, 4-(5-deoxy-α-l-arabinofuranosyl)-2-phenyl-ν-triazole (4) and 4-(5-deoxy-β-l-arabinofuranosyl)-2-phenyl-ν-triazole (5). The structure and anomeric configurations of 2, 4, and 5 were determined by n.m.r. spectroscopy. The preponderant conformation of 4 and 5, and the mass spectra of 2, 4, and 5 are discussed.     

Regioselective and stereoselective benzoylation of 2-N-protected 4,6-O-ketal derivatives of D-glucosamines with 1-(benzoyloxy)benzotriazole

A highly regioelective and stereoselective benzoylation of the 2-N-protected 4,6-O-ketal derivatives of D-glucosamines with 1-(benzoyloxy)benzotriazole that affords the corresponding beta anomeric benzoates in excellent yields is described herein.     

2''-Deoxy-3,7-dideazaguanosine and related compounds. Synthesis of 6-amino-1-(2-deoxy-beta-D-erythro-pentofuranosyl) and 1-beta-D-arabinofuranosyl-1H-pyrrolo[3,2-c]pyridin-4(5H)-one via direct glycosylation of a pyrrole precursor.

The synthesis of two new analogs of 2'-deoxyguanosine, 6-amino-1-(2-deoxy-beta-D-erythro-pentofuranosyl)-1H-pyrrolo[3,2-c] pyridin-4(5H)-one (8) and 6-amino-1-beta-D-arabinofuranosyl-1H-pyrrolo[3,2-c]-pyridin-4(5H)-one (13) has been accomplished by glycosylation of the sodium salt of ethyl 2-cyanomethyl-1H-pyrrole-3-carboxylate (4c) using 1-chloro-2-deoxy-3,5-di-O-p-toluoyl-alpha-D-erythro-pentofuranose( 5) and 1-chloro-2,3,5-tri-O-benzyl-alpha-D-arabinofuranose (9), respectively. The resulting blocked nucleosides, ethyl 2-cyanomethyl-1-(2-deoxy-3,5-di-O-p-toluoyl-beta-D-erythro- pentofuranosyl)-1H-pyrrole-3-carboxylate (6) and ethyl 2-cyanomethyl-1-(2,3,5-tri-O-benzyl-beta-D-arabinofuranosyl)- 1H-pyrrole-3-carboxylate, were ring closed with hydrazine to form 5-amino-6-hydrazino-1-(2-deoxy-beta-D-erythro-pentofuranosyl)-1H- pyrrolo[3,2-c]-pyridin-4(5H)-one (7) and 5,6-diamino-1-(2,3,5-tri-O-benzyl-beta-D-arabinofuranosyl)-1H- pyrrolo[3,2-c]pyridin-4(5H)-one (11), respectively. Treatment of 7 with Raney nickel provided the 2'-deoxyguanosine analog 8 while reaction of 11 with Raney nickel followed by palladium hydroxide/cyclohexene treatment gave the 2'-deoxyguanosine analog 13. The anomeric configuration of 8 was assigned as beta by proton NMR, while that of 13 was confirmed as beta by single-crystal X-ray analysis of the deblocked precursor ethyl 2-cyanomethyl-1-beta-D-arabinofuranosyl-1H-pyrrole-3-carboxylate (10a).     

Discovery of novel 2-[2-(3-hydroxy-pyridin-2-yl)-thiazol-4-yl]-acetamide derivatives as HIF prolyl 4-hydroxylase inhibitors; SAR,synthesis and modeling evaluation

The design, synthesis, and capacity to inhibit HIF prolyl 4-hydroxylases (PHDs) are described for 2-[2-(3-hydroxy-pyridin-2-yl)-thiazol-4-yl]-acetamide analogs. These analogs revealed two kinds of novel scaffolds as PHD2 inhibitors. Synthetic routes were developed for the preparation of their analogs containing the new scaffolds. In addition, the structure–activity relationship (SAR) of the 2-[2-(3-hydroxy-pyridin-2-yl)-thiazol-4-yl]-acetamide derivatives and their biological activities were reported. The complex structure of compound 18 with PHD2 was also obtained for the purpose of more efficient lead optimization.     

The specificity of viral and bacterial sialidases for alpha(2-3)- and alpha(2-6)-linked sialic acids in glycoproteins

The anomeric specificity of six sialidases (Vibrio cholerae, Arthrobacter ureafaciens, Clostridium perfringens, Newcastle disease virus, fowl plague virus and influenza A2 virus sialidases) was assessed with sialylated antifreeze glycoprotein, ovine submandibular gland glycoprotein and alpha 1-acid glycoprotein, resialylated specifically in alpha(2-3) or alpha(2-6) linkage with N-acetylneuraminic acid or N-glycolylneuraminic acid using highly purified sialyltransferases. The rate of release of sialic acid from these substrates was found to correlate well with the specificity observed earlier with the same sialidases using small oligosaccharide substrates, i.e., alpha(2-3) glycosidic linkages are hydrolyzed faster than alpha(2-6) linkages, with the exception of the enzyme from A. ureafaciens. Sialidase activity was higher with N-acetylneuraminic acid when compared with N-glycolylneuraminic acid. The studies also showed that the core oligosaccharide and protein structure in glycoproteins may influence the rate of release for different glycosidic linkages.     

Tandem Radical Cyclization-Oxygenation of 6-(2,2-Di-bromovinyl)-1-(2-deoxy-d-erytho-pent-1-enofuranosyl)-uracil: Synthesis of Anomeric Spiro Nucleosides Having Arabino and Ribo Configurations

Abstract

Radical-mediated 5-exo-trig cyclization of 6-(2,2-dibromovinyl)-1-(2-deoxy-D-erythro-pent-1-enofuranosyl)uracil, when carried out in the presence of oxygen, furnished an anomeric spiro nucleoside having arabino-configuration. The corresponding ribofuranosyl analogue was also synthesized via the 2′-keto derivative.

     

Synthesis of a novel C-nucleoside, 2-amino-7-(2-deoxy-beta-D-erythro- pentofuranosyl)-3H,5H-pyrrolo-[3,2-d]pyrimidin-4-one (2'-deoxy-9-deazaguanosine).

A synthesis of the C-nucleoside, 2-amino-7-(2-deoxy-beta-D-erythro- pentofuranosyl)-3H,5H-pyrrolo[3,2-d]pyrimidin-4-one (9-deaza-2'-deoxyguanosine) was achieved starting from 2-amino-6-methyl-3H-pyrimidin-4-one (5) and methyl 2-deoxy-3,5-di-O-(p-nitrobenzoyl)-D-erythro-pento-furanoside (11). The anomeric configuration of the C-nucleoside was established by 1H NMR, NOEDS and ROESY. This C-nucleoside did not inhibit the growth of T-cell lymphoma cells.     

Amplification of depolarization-induced and ryanodine-sensitive cytosolic Ca2+ elevation by synthetic carbocyclic analogs of cyclic ADP-ribose and their antagonistic effects in NG108-15 neuronal cells

We synthesized analogs modified in the ribose unit (ribose linked to N1 of adenine) of cyclic ADP-ribose (cADPR), a Ca2+-mobilizing second messenger. The biological activities of these analogs were determined in NG108-15 neuroblastoma x glioma hybrid cells that were pre-loaded with fura-2 acetoxymethylester and subjected to whole-cell patch-clamp. Application of the hydrolysis-resistant cyclic ADP-carbocyclic-ribose (cADPcR) through patch pipettes potentiated elevation of the cytoplasmic free Ca2+ concentration ([Ca2+]i) at the depolarized membrane potential. The increase in [Ca2+]i evoked upon sustained membrane depolarization was significantly larger in cADPcR-infused cells than in non-infused cells and its degree was equivalent to or significantly greater than that induced by cADPR or beta-NAD+. 8-Chloro-cADPcR and two inosine congeners (cyclic IDP-carbocyclic-ribose and 8-bromo-cyclic IDP-carbocyclic-ribose) did not induce effects similar to those of cADPcR or cADPR. Instead, 8-chloro-cADPcR together with cADPR or cADPcR caused inhibition of the depolarization-induced [Ca2+]i increase as compared with either cADPR or cADPcR alone. These results demonstrated that our cADPR analogs have agonistic or antagonistic effects on the depolarization-induced [Ca2+]i increase and suggested the presence of functional reciprocal coupling between ryanodine receptors and voltage-activated Ca2+ channels via cADPR in mammalian neuronal cells.     

Benzimidazole 2′-Isonucleosides: Design,Synthesis, and Antiviral Activity of 2-Substituted-5,6-Dichlorobenzimidazole 2′-Isonucleosides

Abstract

2,5,6-Trihalogenated benzimidazole-β-D-ribofuranosyl nucleosides and 2-substituted amino-5,6-dichlorobenzimidazole-β-L-ribofuranosyl nucleosides are potent and selective inhibitors of human cytomegalovirus (HCMV). The D-ribofuranosyl analogs are metabolized rapidly in vivo rendering them unsuitable as drug candidates. The primary source of instability is thought to be the anomeric bond. The synthesis of a series of chemically stable benzimidazole-2′-isonucleosides is presented. The synthetic schemes employed are based on nucleophilic displacements of a 2′-tosylate from carbohydrate intermediates with 2-bromo-5,6-dichlorobenzidazole. 2-Bromo and 2-isopropyl amino analogs with 3′- and 5′-oxo and deoxy substitutions were prepared. The benzimidazole-2′-isonucleosides presented here demonstrated reduced activity against HCMV when compared to other D-ribofuranosyl benzimidazole analogs. In addition, they were not found to be inhibitors of HIV.