An improved synthesis of rupintrivir (AG7088) was accomplished using three amino acids (L-glutamic acid,
D-4-fluorophenylalanine, and L-valine) as the building blocks. The key fragment ketomethylene dipeptide isostere was constructed
with the valine derivative and phenylpropionic acid derivative, followed by coupling with a lactam derivative and an
isoxazole acid chloride to provide AG7088 totally in eight steps.