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.

Tailored thioxanthone‐based photoinitiators for two‐photon‐controllable polymerization and nanolithographic printing

“…S1–S3). Dibromothioxanthen‐9‐one (DBTX) can be synthesized through a bromination reaction . BDAPT and DAPT can be successfully formed by traditional Sonogashira coupling reactions using a single step .…”

“…26,28 Dibromothioxanthen-9-one (DBTX) can be synthesized through a bromination reaction. [29][30][31] BDAPT and DAPT can be successfully formed by traditional Sonogashira coupling reactions using a single step. 26,28,32 The major product of these reactions (i.e., either the di-substituted BDAPT or mono-substituted DAPT) can be controlled by changing the ratio of two different starting materials.…”

Photoremovable Protecting Groups in Chemistry and Biology: Reaction Mechanisms and Efficacy

“…319 Moreover, some of these compounds proved to be suitable for deprotection under irradiation with 350 nm light. For example, 5′- O -(3-methoxy-9-phenylthioxanthyl)-2′-deoxythymidine ( 172 , Scheme 68) quantitatively releases thymidine by irradiation at 300 or 350 nm.…”

Photolabile Protecting Groups in Organic Synthesis

“…The photochemically promoted rupture of a benzylic carbon-heteroatom bond is exploited in numerous photolabile protecting groups, for example in the 9-phenylxanthen-9-yl (also called pixyl group, X ¼ O in Scheme 13.11) [40] and its sulfur- containing analogue (S-pixyl, X ¼ S) [41,42], which are used in oligonucleotide synthesis. Based on the same principles, derivatives of anthraquinone (aqmoc) [43], pyrene [44], coumarin [45][46][47][48][49][50][51][52][53], and phenanthrene have each been used in certain instances (Scheme 13.12) [54].…”