Glycocalix[4]arenes and their affinity to a library of galectins: the linker matters

Galectins are lectins that bind β-galactosides. They are involved in important extra- and intracellular biological processes such as apoptosis, and regulation of the immune system or the cell cycle. High-affinity ligands of galectins may introduce new therapeutic approaches or become new tools for biomedical research. One way of increasing the low affinity of β-galactoside ligands to galectins is their multivalent presentation, e.g., using calixarenes. We report on the synthesis of glycocalix[4]arenes in cone, partial cone, 1,2-alternate, and 1,3-alternate conformations carrying a lactosyl ligand on three different linkers. The affinity of the prepared compounds to a library of human galectins was determined using competitive ELISA assay and biolayer interferometry. Structure-affinity relationships regarding the influence of the linker and the core structure were formulated. Substantial differences were found between various linker lengths and the position of the triazole unit. The formation of supramolecular clusters was detected by atomic force microscopy. The present work gives a systematic insight into prospective galectin ligands based on the calix[4]arene core.

Bacterial Aryl Sulfotransferases in Selective and Sustainable Sulfation of Biologically Active Compounds using Novel Sulfate Donors

Regioselective sulfation of bioactive compounds is a vital and scarcely studied topic in enzyme-catalyzed transformations and metabolomics. The major bottleneck of enzymatic sulfation consists in finding suitable sulfate donors. In this regard, 3'-phosphoadenosine 5'-phosphosulfate (PAPS)-independent aryl sulfotransferases using aromatic sulfate donors are a favored choice due to their cost-effectiveness. This work presents a unique study of five sulfate donors differing in their leaving group pK_a values with a new His-tagged construct of aryl sulfotransferase from Desulfitobacterium hafniense (DhAST-tag). DhAST-tag was purified to homogeneity and biochemically characterized. Two new donors (3-nitrophenyl sulfate and 2-nitrophenyl sulfate) were synthesized. The kinetic parameters of these and other commercial sulfates (4-nitrophenyl, 4-methylumbelliferyl, and phenyl) revealed large differences with respect to the structure of the leaving group. These donors were screened for the sulfation of selected flavonoids (myricetin, chrysin) and phenolic acids (gallate, 3,4-dihydroxyphenylacetate). The donor impact on the sulfation regioselectivity and yield was assessed. The obtained regioselectively sulfated compounds are authentic human metabolites required as standards in clinical trials.