Asymmetric Synthesis of Prodrug Nucleotides (ProTides): Construction of the P-Stereogenic Centers

As an antivirus drug, remdesivir is currently in clinical studies for the treatment of COVID-19. Remdesivir is a prodrug originally developed by Gilead for the treatment of Ebola. The prodrug nucleotide (ProTide) technology is a prodrug-designing strategy developed by McGuigan and co-workers, in which a phosphoramidate side-chain is covalently attached to the hydroxy group of a drug molecule in order to enhance the cell permeability and metabolic activation efficiency. This approach has proved to be very successful in the identification of nucleoside analogues with antiviral or antitumor activities. It is also adapted in the application of non-nucleoside agents, such as neurodegeneration therapeutics, further demonstrating its usefulness in drug discovery. The chirality of the pentavalent phosphorous plays a significant role in the bioactivity of a ProTide molecule. Therefore, the efficient synthesis of such chemical scaffold in a highly enantioselective manner is very desirable and has intrigued great interests from both academia and pharmaceutical industry. In this review, based on the reactions employing optically pure P(V) precursors or P-racemic P(V) precursors, the recent advances on the stereoselective assembly of ProTide compounds are summarized. Various innovative strategies, including (dynamic) kinetic resolutions, were implemented to construct the vital P-stereogenic center with high regio- and stereo-selectivity. It is notable that several methods could be performed at kilogram scale, which are highlighted to showcase their practical values in the process chemistry. The asymmetric synthesis of enantiopure phosphoramidate precursors is illustrated in detail which will be informative for future drug development. Moreover, the clinical performance of some investigational ProTide drugs is also briefly discussed.