Pixyl group

The pixyl ether is prepared from the xanthenyl chloride in 68-87% yield. This group has been used extensively in the protection of the 5 -OH of nucleosides it is readily cleaved by acidic hydrolysis (80% AcOH, 20°, 8-15 min, 100% yield, or 3% trichloroacetic acid). It can be cleaved under neutral conditions with ZnBrj, thus reducing the extent of the often troublesome depurination of A -6-benzyloxy-adenine residues during deprotection. Conditions which remove the pixyl group also partially cleave the THP group (t,/2 for THP at 2 -OH of ribonucleoside = 560 s in 3% Cl2CHC02H/CH2Cl2). ... 

The 9-phenylthioxanthyl (S-pixyl) group is a photocleavable 5 -OH protecting group for deoxyribonucleosides <99TL7911>. 

The photochemicaHy promoted rupture of a benzylic carbon-heteroatom bond is exploited in numerous photolabile protecting groups, for example in the 9-phenyl-xanthen-9-yl (also called pixyl group, X = O in Scheme 13.11) [40] and its sulfur-... 

Coleman, M.P. and Boyd, M.K. (1999) The S-pixyl group an efficient photocleavable protecting group for the 5 hydroxy function of deoxyribonucleo-sides. Tetrahedron Letters, 40, 7911-7915. 

Deprotection using photolysis at 254 or 300 nm in aqueous CH3CN can also be used to cleave the pixyl group (83-97% yield). ... 

The removal of modified trityl and of pixyl groups has been carried out by the use of an acidic species generated by the reaction of diethyl oxomalonate with methanol, thought to be the hemiacetal formed by addition of methanol to the ketonic carbonyl. In the case of 2 -deoxy-purine nucleosides depurination occurred competitively. 99 silver ion has been found to have a pronounced effect on the regioselectivity of tritylation of nucleosidic hydroxyl groups.390... 

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