Deprotection studies of novel photocleavable protecting groups

ORGN 124

Garrett M. Zopp, and Mary K. Boyd, Department of Chemistry, Loyola University Chicago, 6525 N. Sheridan Rd., Chicago, IL 60626
The 9-phenylthioxanthyl moiety (S-pixyl) is an effective protecting group (PG) for primary alcohols. It can be cleaved from the parent alcohol by photochemical methods in addition to acid catalyzed cleavage. Its regioselectivity allows specific protection of the 5′-hydroxyl versus the 3′-hydroxyl moiety in deoxyribonucleosides. Previous photodeprotection studies for 5′-S-pixyl-protected thymidine included the investigation of S-pixyl analogues incorporating substitution on the 9-aryl ring or the thioxanthyl backbone. These analogues gave excellent deprotection yields, exhibited absorption at higher wavelengths and required shorter irradiation times when compared to the underivatized S-pixyl and the analogous 9-phenylxanthyl (pixyl) moiety. Several S-pixyl analogues have been synthesized to determine the effects of combining substitution both on the thioxanthyl backbone and 9-aryl ring. Each analogue has been used to protect the 5′-hydroxyl moiety of thymidine to gain a direct comparison to the previous studies. Synthetic routes and deprotection results will be discussed.