Selenosugars targeting the infective stage of Trypanosoma brucei with high selectivity.

Earlier evidences showed that diglycosyl diselenides are active against the infective stage of African trypanosomes (top hits IC50 0.5 and 1.5 µM) but poorly selective (selectivity index <10). Here we extended the study to 33 new seleno-glycoconjugates with the aim to improve potency and selectivity. Three selenoglycosides and three glycosyl selenenylsulfides displayed IC50 against bloodstream Trypanosoma brucei in the sub-µM range (IC50 0.35-0.77 µM) and four of them showed an improved selectivity (selectivity index >38-folds vs. murine and human macrohages). For the glycosyl selenylsulfides, the anti-trypanosomal activity was not significantly influenced by the nature of the moiety attached to the sulfur atom. Except for a quinoline-, and to a minor extent a nitro-derivative, the most selective hits induced a rapid (within 60 min) and marked perturbation of the LMWT-redox homeostasis. The formation of selenenylsulfide glycoconjugates with free thiols has been identified as a potential mechanism involved in this process.

Saturation Transfer Difference NMR and Molecular Docking Interaction Study of Aralkyl-Thiodigalactosides as Potential Inhibitors of the Human-Galectin-3 Protein.

Human Galectin-3 (hGal-3) is a protein that selectively binds to ß-galactosides and holds diverse roles in both normal and pathological circumstances. Therefore, targeting hGal-3 has become a vibrant area of research in the pharmaceutical chemistry. As a step towards the development of novel hGal-3 inhibitors, we synthesized and investigated derivatives of thiodigalactoside (TDG) modified with different aromatic substituents. Specifically, we describe a high-yielding synthetic route of thiodigalactoside (TDG); an optimized procedure for the synthesis of the novel 3,3'-di-O-(quinoline-2-yl)methyl)-TDG and three other known, symmetric 3,3'-di-O-TDG derivatives ((naphthalene-2yl)methyl, benzyl, (7-methoxy-2H-1-benzopyran-2-on-4-yl)methyl). In the present study, using competition Saturation Transfer Difference (STD) NMR spectroscopy, we determined the dissociation constant (Kd) of the former three TDG derivatives produced to characterize the strength of the interaction with the target protein (hGal-3). Based on the Kd values determined, the (naphthalen-2-yl)methyl, the (quinolin-2-yl)methyl and the benzyl derivatives bind to hGal-3 94, 30 and 24 times more strongly than TDG. Then, we studied the binding modes of the derivatives in silico by molecular docking calculations. Docking poses similar to the canonical binding modes of well-known hGal-3 inhibitors have been found. However, additional binding forces, cation-π interactions between the arginine residues in the binding pocket of the protein and the aromatic groups of the ligands, have been established as significant features. Our results offer a molecular-level understanding of the varying affinities observed among the synthesized thiodigalactoside derivatives, which can be a key aspect in the future development of more effective ligands of hGal-3.

Synthesis of Tetravalent Thio- and Selenogalactoside-Presenting Galactoclusters and Their Interactions with Bacterial Lectin PA-IL from Pseudomonas aeruginosa.

Synthesis of tetravalent thio- and selenogalactopyranoside-containing glycoclusters using azide-alkyne click strategy is presented. Prepared compounds are potential ligands of Pseudomonas aeruginosa lectin PA-IL. P. aeruginosa is an opportunistic human pathogen associated with cystic fibrosis, and PA-IL is one of its virulence factors. The interactions of PA-IL and tetravalent glycoconjugates were investigated using hemagglutination inhibition assay and compared with mono- and divalent galactosides (propargyl 1-thio- and 1-seleno-ß-d-galactopyranoside, digalactosyl diselenide and digalactosyl disulfide). The lectin-carbohydrate interactions were also studied by saturation transfer difference NMR technique. Both thio- and seleno-tetravalent glycoconjugates were able to inhibit PA-IL significantly better than simple d-galactose or their intermediate compounds from the synthesis.

Isolation of ß-Cryptoxanthin-epoxides, Precursors of Cryptocapsin and 3'-Deoxycapsanthin, from Red Mamey (Pouteria sapota).

From an extract of red mamey (Pouteria sapota) ß-cryptoxanthin-5,6-epoxide, ß-cryptoxanthin-5',6'-epoxide, 3'-deoxycapsanthin, and cryptocapsin were isolated and characterized by UV-vis spectroscopy, electronic circular dichroism (ECD), nuclear magnetic resonance (NMR) spectroscopy, and mass spectrometry (MS). Epoxidation of ß-cryptoxanthin delivered the ß-(5'R,6'S)- and (5'S,6'R)-cryptoxanthin-5',6'-epoxides, which were identified by HPLC-ECD analysis. These carotenoids among others are quite common in the fruits of Central America, and as they are natural provitamins A, they should play an important role in the diet of the mostly vitamin A deficient population of this region.

Photoinitiated hydrothiolation of pyranoid exo-glycals: the d-galacto and d-xylo cases.

Radical-mediated addition reactions of thiols to O-peracetylated exo-galactal and exo-xylal with 2,2-dimethoxy-2-phenylacetophenone as the photoinitiator resulted in high yielding formation of the corresponding ß-d-glycopyranosylmethyl-sulfide derivatives (2,6-anhydro-1-deoxy-1-S-substituted-1-thio-alditols) with exclusive regio- and very high stereoselectivity, including disaccharide mimicks with Gly-CH2-S-Gly scaffolds.

Preparation of neuroprotective condensed 1,4-benzoxazepines by regio- and diastereoselective domino Knoevenagel-[1,5]-hydride shift cyclization reaction.

Condensed O,N-heterocycles containing tetrahydro-1,4-benzoxazepine and tetrahydroquinoline moieties were prepared by a regio- and diastereoselective domino Knoevenagel-[1,5]-hydride shift cyclization reaction of a 4-aryl-2-phenyl-1,4-benzoxazepine derivative obtained from flavanone. The relative configuration of products were determined by the correlation of (3) J H,H coupling data with the geometry of major conformers accessed by DFT conformational analysis. Separated enantiomers of the products were characterized by HPLC-ECD data, which allowed their configurational assignment on the basis of TDDFT-ECD calculation of the solution conformers. Two compounds showed neuroprotective activities against hydrogen peroxide (H2O2) or ß-amyloid25-35 (Aß25-35)-induced cellular injuries in human neuroblastoma SH-SY5Y cells in the range of those of positive controls.

Aromatic glycosyl disulfide derivatives: evaluation of their inhibitory activities against Trypanosoma cruzi.

Aromatic oligovalent glycosyl disulfides and some diglycosyl disulfides were tested against three different Trypanosoma cruzi strains. Di-(ß-D-galactopyranosyl-dithiomethylene) benzenes 2b and 4b proved to be the most active derivatives against all three strains of cell culture-derived trypomastigotes with IC50 values ranging from 4 to 11 µM at 37 °C. The inhibitory activities were maintained, although somewhat lowered, at a temperature of 4 °C as well. Three further derivatives displayed similar activities against at least one of the three strains. Low cytotoxicities of the active compounds, tested on confluent HeLa, Vero and peritoneal macrophage cell cultures, resulted in significantly higher selectivity indices (SI) than that of the reference drug benznidazole. Remarkably, several molecules of the tested panel strongly inhibited the parasite release from T. cruzi infected HeLa cell cultures suggesting an effect against the intracellular development of T. cruzi amastigotes as well.

Cryptocapsinepoxide-type carotenoids from red mamey, Pouteria sapota.

New carotenoids, cryptocapsin-5,6-epoxide, 3'-deoxycapsanthin-5,6-epoxide, and cryptocapsin-5,8-epoxides, have been isolated from the ripe fruits of red mamey (Pouteria sapota). Cryptocapsin-5,6-epoxide was prepared by partial synthesis via epoxidation of cryptocapsin, and the (5R,6S)- and (5S,6R)-stereoisomers were identified by HPLC-ECD analysis. Spectroscopic data of the natural (anti) and semisynthetic (syn) derivatives obtained by acid-catalyzed rearrangement of cryptocapsin-5,8-epoxide stereoisomers were compared for structural elucidation. Chiral HPLC separation of natural and semisynthetic samples of cryptocapsin-5,8-epoxides was performed, and HPLC-ECD analysis allowed configurational assignment of the separated stereoisomers.

Convenient syntheses of 1,2-trans selenoglycosides using isoselenuronium salts as glycosylselenenyl transfer reagents.

Se-glycosyl-isoselenuronium salts such as three and four which can be prepared in one high-yielding step from acetohalogeno sugars proved to be convenient starting materials for the syntheses of a variety of selenoglycosides. Reaction with (ar)alkyl halides proceeds under mild conditions, in short time, at room temperature to afford the corresponding selenoglycosides in good yields. Aryl halides react to appreciable extent only if bearing activating nitro groups on the aromatic ring. Reactions with acylating reagents such as acetic anhydride and benzoyl chlorides furnished anomeric selenoesters some of which were recently proposed as starting compounds for alternative selenoglycoside syntheses. Selenodisaccharides with two different monosaccharide units could also be prepared via reactions of glycosyl-isoselenuronium salts with monosaccharide derivatives bearing primary or secondary triflate groups.

Electrospray ionization mass spectrometric analysis of highly reactive glycosyl halides.

Highly reactive glycosyl chlorides and bromides have been analysed by a routine mass spectrometric method using electrospray ionization and lithium salt adduct-forming agents in anhydrous acetonitrile solution, providing salient lithiated molecular ions [M+Li]⁺, [2M+Li]⁺ etc. The role of other adduct-forming salts has also been evaluated. The lithium salt method is useful for accurate mass determination of these highly sensitive compounds.

Glycosylation via mixed disulfide formation using glycosylthio-phthalimides and -succinimides as glycosylsulfenyl-transfer reagents.

The silver salts of tetra-O-acetyl α- or -ß-D-glycopyranosyl thiols 1a-4a react smoothly with N-bromophthalimide and N-bromosuccinimide to furnish glycosylthio-phthalimide (1b-4b) and -succinimide (1c-3c) derivatives. Reactions of these reagents with aliphatic, aromatic, and glycosyl thiols as well as with cysteine and glutathione result in the formation of glycosylated mixed disulfides under mild conditions and in good yields. The S-glycosyl-N-acylsulfenamides described here represent novel, convenient glycosylsulfenyl-transfer reagents in effecting glycosylation of various thiols, including sugars, amino acids and peptides, through disulfide formation and can, therefore, be useful in controlled glycosylation of proteins as well.

Experimental and computational studies of nJ(77Se, 1H) selenium-proton couplings in selenoglycosides.

Selenoglycosides are important starting materials in synthetic carbohydrate chemistry and play a role in biological interactions as well. Both aspects are influenced by the conformation around the glycosidic bond. Here, we present a combined experimental and computational approach to measure and evaluate (n)J((77)Se, (1)H) coupling constants for their use in conformational analysis. The measurements were carried out using a modified CPMG-HSQMBC pulse scheme which yields pure absorption antiphase multiplets to allow accurate determination of the (n)J(XH) values regardless of the size of the proton-proton couplings. Theoretical calculations were performed at the Second-Order Polarization Propagator Approach (SOPPA) level. Population-averaged values calculated for geminal and vicinal couplings are in a good agreement with experiment indicating an adequate theoretical level of the calculations. Experimental observations and computations alike have indicated that two-bond (77)Se-(1)H couplings, (2)J((77)Se, (1)H), in a H1-C1-Se-X moiety are very sensitive to the torsion angle around the C1-Se-bond and will, therefore, be useful for conformational studies.

Circular dichroism of diglycosyl dichalcogenides in solution and solid state.

Solution and solid-state CD spectra of nine peracetylated and deacetalyted diglycosyl disulfides were measured to study the relationship between the low-energy CD transitions (n1-->sigma*(S--S) and n2-->sigma*(S--S)) and helicity of the inherently chiral disulfide chromophore as perturbed by chiral carbohydrate moieties. The solid-state CD spectra were directly correlated with the reported X-ray structures of Ac4GlcSSGlcAc4 and Ac4GlcSSGalAc4, and the CD data revealed that all the disulfides have M helicity with C1--S--S--C1' dihedral angles -90 degrees < phi < 0 degrees both in solution and in the solid state. A TDDFT CD study was carried out on dimethyl diselenide which confirmed that the same quadrant rule is relevant between the signs of the low-energy CD transitions and the diselenide torsional angle as formulated previously for the disulfide chromophore. The CD spectra of Ac4GlcSeSeGlcAc4 measured in solution and in the solid state were correlated with its X-ray structure and reproduced well by TDDFT CD calculations performed on its tetra-O-acetyl derivative.

Synthesis of ketopyranosyl glycosides and determination of their anomeric configuration on the basis of the three-bond carbon-proton couplings.

Anomeric pairs of ketopyranosyl glycosides with various substituents at C(alpha), C(beta) and C(gamma) were synthesized from the corresponding thioglycosides, and the influence of the C(alpha)-C(beta)-C(gamma)-H(gamma) torsion angle and substituent effects on the three-bond carbon-proton couplings was studied. The cis coupling constants range from 1 to 2Hz. The trans couplings are generally as small as 2.3-2.6Hz; however, for compounds bearing an unsubstituted gamma-carbon, a relatively large trans coupling was measured (4.8Hz). An S-ethyl group at the beta-position increases the cis coupling (up to 3.2Hz) compared to the corresponding O-glycosides.

Novel approaches to the syntheses of N-substituted S-glycosyl-sulfenamides.

Bis(tetra-O-acetyl-beta-D-glucopyranosyl)disulfide reacts, under silver ion activation, with primary and secondary aliphatic as well as aromatic amines to furnish the title compounds in moderate to good yields. The same derivatives could also be obtained from (tetra-O-acetyl)-beta-D-glucopyranosyl methanethiolsulfonate 1 by nucleophilic substitution with amines. It was shown that the polarization of the S-S-bond in 1 is enhanced by Ag+ so as to allow reaction with sterically hindered amines as well.