title: Thermolytic 4-methylthio-1-butyl group for phosphate/thiophosphate protection in solid-phase synthesis of DNA oligonucleotides.
abstract: The thermolabile 4-methylthio-1-butyl phosphate/thiophosphate protecting group for DNA oligonucleotides has been investigated for its potential application to a "heat-driven" process for either oligonucleotide synthesis on diagnostic microarrays or, oppositely, to the large-scale preparation of therapeutic oligonucleotides. The preparation of phosphoramidites 10a-d is straightforward, and the incorporation of these amidites into oligonucleotides via solid-phase techniques proceeds as efficiently as that achieved with 2-cyanoethyl deoxyribonucleoside phosphoramidites. The versatility of the 4-methylthio-1-butyl phosphate/thiophosphate protecting group is exemplified by its facile removal from oligonucleotides upon heating for 30 min at 55 degrees C in an aqueous buffer under neutral conditions or within 2 h at 55 degrees C in concentrated NH(4)OH. The deprotection reaction occurs through an intramolecular cyclodeesterification mechanism leading to the formation of sulfonium salt 18. When mixed with deoxyribonucleosides and N-protected 2'-deoxyribonucleosides or with a model phosphorothioate diester under conditions approximating those of large-scale (>50 mmol) oligonucleotide deprotection reactions, the salt 18 did not significantly alter DNA nucleobases or desulfurize the phosphorothioate diester model to an appreciable extent.
authors.affiliation: Division of Therapeutic Proteins, Center for Drug Evaluation and Research, Food and Drug Administration, 8800 Rockville Pike, Bethesda, Maryland 20892, USA.
authors.forename: Jacek
authors.initials: J
authors.lastname: Cieślak
authors.forename: Andrzej
authors.initials: A
authors.lastname: Grajkowski
authors.forename: Victor
authors.initials: V
authors.lastname: Livengood
authors.forename: Serge L
authors.initials: SL
authors.lastname: Beaucage
mesh_terms: D001483:Base Sequence; D002384:Catalysis; D004247:DNA / Q000737:chemistry*; D003853:Deoxyribonucleosides / Q000138:chemical synthesis* / Q000737:chemistry; D004591:Electrophoresis, Polyacrylamide Gel; D006358:Hot Temperature; D008958:Models, Molecular; D015394:Molecular Structure; D009946:Organothiophosphorus Compounds / Q000737:chemistry*; D010710:Phosphates; D013873:Thionucleotides / Q000737:chemistry
chemical_list: D003853:Deoxyribonucleosides; D009946:Organothiophosphorus Compounds; D010710:Phosphates; D013873:Thionucleotides; D004247:DNA; C035638:thiophosphoric acid