EVALUATION OF 3-ETHOXY-1,2,4-DITHIAZOLINE-5-ONE (EDITH) AS A NEW SULFURIZING REAGENT IN COMBINATION WITH LABILE EXOCYCLIC AMINO PROTECTING GROUPS FOR SOLID-PHASE OLIGONUCLEOTIDE SYNTHESIS

3-ethoxy-1,2,4-dithiazoline-5-one (EDITH) was recently introduced as a n efficient sulfurizing reagent for solid-phase oligonucleotide synthe sis, The successful syntheses were performed using standard base prote cting groups (i.e. benzoyl for A and C, isobutyryl for G), which requi red deprotection in concentrated ammonium hydroxide at 55 degrees C fo r 15-18 h, We have explored the possibility of using EDITH in combinat ion with fast deprotection chemistry (e.g. Expedite Chemistry using te rt-butylphenoxy acetyl as a base protecting group). Surprisingly, poor synthesis performance was observed when syntheses were conducted with EDITH, Expedite Chemistry and standard synthesis cycle (i.e. Coupling -Thio-Cap), Potential G modification seemed to be the source of incomp atibility since sequences containing no G or carrying isobutyryl-prote cted G residues could be synthesized with high efficiency. However, th e deleterious G modification can be readily eliminated by inserting a capping step before the sulfurization reaction. Oligomers prepared wit h the Coupling-Cap-Thio-Cap cycle contained few phosphodiester contami nants as measured by P-31-NMR, anion-exchange HPLC and MALDI-TOF mass spectrometry, In addition to reducing deprotection time, this new comb ination also provides a mild method for the preparation of certain pho sphorothioate oligomers that may be sensitive to prolonged ammonia tre atment (e.g. thioated RNAs).