An improved procedure is reported for the asymmetric synthesis of urac
il polyoxin C (UPOC) from 2',3'-O-isopropylideneuridine-5'-aldehyde. T
he methodology described here is based on the highly diastereocontroll
ed formation of 1-(beta-D-allofuranosyl)uracil and its facile conversi
on into the corresponding 2,5'-O-cyclouridine derivative, a key step f
or the stereocontrolled formation of the terminal alpha-amino acid of
UPOC.