Synthesis of silodosin glucuronide and its deuterated counterpart: solving a problematic O-glycosylation of a nitrogen-containing molecule

We report here the first chemical synthesis of silodosin glucuronide, a metabolite of the alpha(1A)-adrenoceptor antagonist silodosin, and its deuterium-labeled counterpart. As a key synthetic step, the incorporation of a glucuronosyl unit onto silodosin invariably led to either an undesired orthoester or a complex mixture under an array of standard glycosylation conditions. This problematic O-glycosylation may be attributed to the presence of multiple basic groups that could neutralize the acidic activators, decrease the nucleophilicity of a hydroxy group via hydrogen bond or even facilitate acyl migration side reactions. After elaborate tuning of reaction conditions, success was eventually achieved by using perbenzoylated D-glucuronosyl N-phenyltrifluroacetimidate (PTFA) as donor in combination with a procedure of sequential addition of TMSOTf. This protocol is potentially general for the glycosylation of other nitrogen-containing small molecule drugs.