Galectin-3-Binding Glycomimetics that Strongly Reduce Bleomycin-Induced Lung Fibrosis and Modulate Intracellular Glycan Recognition.

Discovery of glycan-competitive galectin-3-binding compounds that attenuate lung fibrosis in a murine model and that block intracellular galectin-3 accumulation at damaged vesicles, hence revealing galectin-3-glycan interactions involved in fibrosis progression and in intracellular galectin-3 activities, is reported. 3,3'-Bis-(4-aryltriazol-1-yl)thiodigalactosides were synthesized and evaluated as antagonists of galectin-1, -2, -3, and -4 N-terminal, -4 C-terminal, -7 and -8 N-terminal, -9 N-terminal, and -9 C-terminal domains. Compounds displaying low-nanomolar affinities for galectins-1 and -3 were identified in a competitive fluorescence anisotropy assay. X-ray structural analysis of selected compounds in complex with galectin-3, together with galectin-3 mutant binding experiments, revealed that both the aryltriazolyl moieties and fluoro substituents on the compounds are involved in key interactions responsible for exceptional affinities towards galectin-3. The most potent galectin-3 antagonist was demonstrated to act in an assay monitoring galectin-3 accumulation upon amitriptyline-induced vesicle damage, visualizing a biochemically/medically relevant intracellular lectin-carbohydrate binding event and that it can be blocked by a small molecule. The same antagonist administered intratracheally attenuated bleomycin-induced pulmonary fibrosis in a mouse model with a dose/response profile comparing favorably with that of oral administration of the marketed antifibrotic compound pirfenidone.

Enantiodivergent Synthesis of Bis-Spiropyrrolidines via Sequential Interrupted and Completed (3 + 2) Cycloadditions.

Both (5R)- and (5S)-1,7-diazaspiro[4.4]nonan-6-ones are obtained via a sequence of interrupted and completed stepwise (3 + 2) cycloadditions between azomethine ylides and π-deficient alkenes. The only source of chirality along the whole process is an enantiopure ferrocenyl pyrrolidine catalytic ligand. When the starting imine incorporates two aryl groups or one aryl group with one electron-releasing substituent, the reaction between the azomethine ylide and the alkene stops at the first step, leading to the corresponding Michael adduct. When imines derived from p-methoxybenzaldehyde are used, the corresponding syn-α-amino-γ-nitro ester is obtained with almost complete enantiocontrol. In contrast, imines derived from benzophenone lead to the corresponding anti analogue. From this interrupted (3 + 2) cycloaddition, cis- and trans-α-amino-γ-lactams can be obtained via hydrogenation of the nitro group followed by in situ cyclization. Imines derived from these latter compounds are the precursors of N-metalated azomethine ylides from which up to four new chiral centers can be generated via completed (3 + 2) cycloaddition reactions with full regio- and diastereocontrol. Cis- and trans-γ-lactams lead to opposite bis-spiropyrrolidine enantiomers. Therefore, both enantiomeric series of spiro compounds can be obtained by means of the same catalytic system. The potential of these rigid, densely substituted homochiral compounds in medicinal chemistry is briefly described.

Monovalent interactions of galectin-1.

Galectin-1, a ß-galactoside binding lectin involved in immunoregulation and cancer, binds natural and many synthetic multivalent glycoconjugates with an apparent glycoside cluster effect, that is, affinity above and beyond what would be expected from the concentration of the determinant sugar. Here we have analyzed the mechanism of such cluster effects in solution at physiological concentration using a fluorescence anisotropy assay with a novel fluorescent high-affinity galectin-1 binding probe. The interaction of native dimeric and monomeric mutants of rat and human galectin-1 with mono- and divalent small molecules, fetuin, asialofetuin, and human serum glycoproteins was analyzed. Surprisingly, high-affinity binding did not depend much on the dimeric state of galectin-1 and thus is due mainly to monomeric interactions of a single carbohydrate recognition domain. The mechanism for this is unknown, but one possibility includes additional interactions that high-affinity ligands make with an extended binding site on the carbohydrate recognition domain. It follows that such weak additional interactions must be important for the biological function of galectin-1 and also for the design of galectin-1 inhibitors.

Synthesis of 3-azido-3-deoxy-beta-D-galactopyranosides.

Three efficient routes to 3-azido-3-deoxy-beta-D-galactopyranosides were developed relying on a double inversion protocol at C3. Two of the routes were demonstrated to work with both O- and S-glycosides. In all three routes, the 2-O-acetyl-3-azido-4,6-O-benzylidene-3-deoxy-beta-D-galactopyranosides were obtained by an azide inversion of the key intermediates 2-O-acetyl-4,6-O-benzylidene-3-O-trifluoromethanesulfonyl-beta-D-gulopyranosides. The intermediate gulopyranosides were in turn obtained from 2-O-acetyl-4,6-O-benzylidene-3-O-trifluoromethanesulfonyl-beta-D-galactopyranosides, installed in one pot from the 4,6-O-benzylidene-beta-D-galactopyranosides, by inversion with nitrite or acetate. For O-glycosides, the gulopyranoside configuration could alternatively be obtained from the 4,6-O-benzylidene-beta-D-galactopyranoside by elimination to give the 2,3-dianhydro derivative followed by a highly stereoselective cis-dihydroxylation.