Development and Implementation of an Aluminum-Promoted Phosphorylation in the Uprifosbuvir Manufacturing Route

A novel application of the synthesis of pronucleotide (ProTide) 5′-phosphoramidate monoesters promoted by aluminum-based Lewis acids is described. In the multikilogram synthesis of uprifosbuvir (MK-3682, 1), a clinical candidate for the treatment of hepatitis C, this methodology provided >100:1 diastereoselectivity at the phosphorus stereocenter and >100:1 selectivity for the 5′-mono phosphorylation over undesired bisphosphorylation side products. The high diastereoselectivity and mono/bis ratio achieved enabled elimination of the tedious workup associated with the tert-butyl magnesium chloride protocol commonly used to install this functionality in similar nucleotide prodrugs, achieving a near doubling of the isolated yield from 45% to 81%. The process development and purity control strategy of MK-3682, as well as handling of the pyrophoric reagent on scale, will also be discussed.