title: S-pixyl analogues as photocleavable protecting groups for nucleosides.
abstract: Several analogues of the 9-phenylthioxanthyl (S-pixyl) photocleavable protecting group have been synthesized, containing substituents on the 9-aryl ring and on the thioxanthyl backbone. Each analogue protected the 5'-hydroxy moiety of thymidine in good to excellent yield. The protected substrates were deprotected in 1:1 water:acetonitrile with irradiation at 300 nm, resulting in recovered thymidine in excellent yield, except for the nitro-substituted analogues which gave substantially lower yields. Substrates with 2,7-dibromo or 3-methoxy substitution on the thioxanthyl backbone were also deprotected efficiently with irradiation at 350 nm. Shorter irradiation times were observed in the less nucleophilic solvent mixture of 1:9 trifluoroethanol:acetonitrile, with no formation of secondary photooxidation products. Photodeprotection with high yields was also achieved in the absence of solvent, with no secondary photoproducts.
authors.affiliation: Department of Chemistry, Loyola University Chicago, Illinois 60626, USA.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Coleman
authors.forename: Mary K
authors.initials: MK
authors.lastname: Boyd
mesh_terms: D004986:Ether / Q000737:chemistry; D015394:Molecular Structure; D009705:Nucleosides / Q000737:chemistry* / Q000528:radiation effects*; D019800:Phenol / Q000737:chemistry; D010782:Photolysis / Q000528:radiation effects*; D012997:Solvents / Q000737:chemistry; D013892:Thioxanthenes; D013936:Thymidine / Q000737:chemistry; D044004:Xanthones / Q000737:chemistry*
chemical_list: D009705:Nucleosides; D012997:Solvents; D013892:Thioxanthenes; D044004:Xanthones; D004986:Ether; D019800:Phenol; C484911:thioxanthone; D013936:Thymidine