title: 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.
abstract: 3-ethoxy-1,2,4-dithiazoline-5-one (EDITH) was recently introduced as an efficient sulfurizing reagent for solid-phase oligonucleotide synthesis. The successful syntheses were performed using standard base protecting groups (i.e. benzoyl for A and C, isobutyryl for G), which required deprotection in concentrated ammonium hydroxide at 55 degrees C for 15-18 h. We have explored the possibility of using EDITH in combination with fast deprotection chemistry(e.g. Expedite Chemistry using tert -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 incompatibility since sequences containing no G or carrying isobutyryl- protected G residues could be synthesized with high efficiency. However, the deleterious G modification can be readily eliminated by inserting a capping step before the sulfurization reaction. Oligomers prepared with the Coupling-Cap-Thio-Cap cycle contained few phosphodiester contaminants as measured by31P-NMR, anion-exchange HPLC and MALDI-TOF mass spectrometry. In addition to reducing deprotection time, this new combination also provides a mild method for the preparation of certain phosphorothioate oligomers that may be sensitive to prolonged ammonia treatment (e.g. thioated RNAs).
authors.affiliation: Innovir Laboratories, Inc., 510 East 73rd Street, New York, NY 10021, USA.
authors.forename: M Y
authors.initials: MY
authors.lastname: Ma
authors.forename: J C
authors.initials: JC
authors.lastname: Dignam
authors.forename: G W
authors.initials: GW
authors.lastname: Fong
authors.forename: L
authors.initials: L
authors.lastname: Li
authors.forename: S H
authors.initials: SH
authors.lastname: Gray
authors.forename: B
authors.initials: B
authors.lastname: Jacob-Samuel
authors.forename: S T
authors.initials: ST
authors.lastname: George
mesh_terms: D015336:Molecular Probe Techniques; D009841:Oligonucleotides / Q000138:chemical synthesis / Q000737:chemistry*; D013844:Thiazoles
chemical_list: C099735:3-ethoxy-1,2,4-dithiazoline-5-one; D009841:Oligonucleotides; D013844:Thiazoles