title: Solid-phase extraction on C18 silica as a purification strategy in the solution synthesis of a 1-thio-beta-D-galactopyranoside library.
abstract: A novel strategy for the purification of carbohydrate-based chemical libraries synthesized in solution was developed. Purification of reaction products was accomplished by means of solid-phase extraction enabled by protecting the 2-, 3-, 4-, and 6-hydroxyl groups of a galactose derivative as their hydrophobic O-laurates. The presence of multiple O-laurates allowed adsorption of reaction products onto C18 silica while reagents and by-products were washed away with MeOH. Products were quantitatively eluted with pentane. Purification of products using solid-phase extraction offers the combined advantages of solution synthesis (normal solution reactivity and ease of reaction monitoring) with those of solid-phase synthesis (facile product isolation permitting the use of large excesses of reagents). To demonstrate the utility of the hydrophobic recovery-procedure, tetra-O-lauroyl-beta-D-galactopyranose-1-thiol was subjected to high-yielding reactions with a panel of Michael-acceptors and an alpha-chloro ketone. The resulting ketone adducts were then either reduced to the alcohols or reductively aminated with a selection of amino acids to give 30 different 1-thio-beta-D-galactosides as mixtures of four diastereomers after removal of protecting groups. At each step, the product was separated from the reagents and their by-products by simple adsorption onto C18 silica, washing with MeOH and elution of product with pentane. After completion of the combinatorial chemistry sequence, the O-laurates were cleaved by methanolysis and the product methyl laurate in turn removed from the desired water-soluble products by C18 adsorption. Individual library members were thus conveniently produced on 10-30 mg scales at purity levels of > 90%. One of the 1-thio-beta-D-galactosides thus produced was found to be a competitive inhibitor of the beta-galactosidase from E. coli with Ki value of 1.7 microM.
authors.affiliation: Department of Chemistry, University of Alberta, Edmonton, Canada.
authors.forename: U J
authors.initials: UJ
authors.lastname: Nilsson
authors.forename: E J
authors.initials: EJ
authors.lastname: Fournier
authors.forename: O
authors.initials: O
authors.lastname: Hindsgaul
mesh_terms: D002236:Carbohydrate Conformation; D004791:Enzyme Inhibitors / Q000138:chemical synthesis / Q000494:pharmacology; D009682:Magnetic Resonance Spectroscopy; D010084:Oxidation-Reduction; D012822:Silicon Dioxide; D012996:Solutions; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D013862:Thiogalactosides / Q000138:chemical synthesis* / Q000494:pharmacology; D001616:beta-Galactosidase / Q000037:antagonists & inhibitors
chemical_list: D004791:Enzyme Inhibitors; D012996:Solutions; D013862:Thiogalactosides; D012822:Silicon Dioxide; C031803:thiodigalactoside; D001616:beta-Galactosidase