Solvent-controlled synthesis of bulky and polar-bulky galactonoamidines

The goal of this study was the design and synthesis of bulky and polar-bulky galactonoamidines that have a potential to interact with both catalytic amino acids in the active site of human α-galactosidase. While a library of more than 25 compounds was previously synthesized following established protocols, the coupling of the selected amines with activated perbenzylated galactothionolactam yielded only small amounts for some of the perbenzylated targets. A computational approach disclosed relative energy differences of selected adducts and suggested a solvent change that then allowed a successful synthesis of the precursor compounds in 20-75%. Subsequent attempts to globally deprotect perbenzylated galactonoamidines by Pd catalyzed hydrogenation resulted in unwanted Pd coordination, incomplete debenzylation reactions, partial compound hydrolysis, and even complete decomposition. A lengthy protocol was elaborated to purify the targeted carbohydrate derivatives after modified debenzylation conditions.