Synthetic route to hydroxypyrrolidine transition state analogues of ribosome-inactivating proteins: (i) DMTrCl (1.5 equiv), DMAP (catalytic), (iPr)2NEt (2 equiv), pyridine, room temperature, 5 h; (ii) 2-cyanoethyl N,N-diisopropylchlorophosphoramidite (2.5 equiv), 2,4,6-collidine (2.5 equiv), 1-methylimidazole (1 equiv), methylene chloride, 0 °C, 30 min; (iii) Expedite DNA/RNA synthesis system. Reproduced from ref 156. Copyright 2004 American Chemical Society.