Download PDF Opens in a new window. Article suggestions will be shown in a dialog on return to ScienceDirect. ... Please enable JavaScript to use all the features on this page. ... The 1,3-dipolar cycloaddition of a chiral nitrone derived from glyoxylic acid and protected d-ribosyl hydroxylamine with the acrylamide of Oppolzer's sultam provides a perfectly stereoselective approach to protected (2R,4R)-4-hydroxy-d-pyroglutamic acid. ... Pyroglutamic acids and ...