Pixyl protecting group

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-... 

Misetic, A. and Boyd, M.K. (1998) The pixyl (Px) group a novel photocleavable protecting group for primary alcohols. Tetrahedron Letters, 39, 1653-1656. 

Coleman, M.P. and Boyd, M.K. (2002) S-Pixyl analogues as photocleavable protecting groups for nucleosides. Journal of Organic Chemistry, 67, 7641-7648. 

The monomers required for the chain assembly are the appropriately protected deoxynucleoside phosphodiesters, such as the triethyl-ammonium salts, illustrated in Fig. 1. The 5 -hydroxyl group of the 2 -deoxyribonucleosides is protected by the use of the very acid-labile protecting groups, 9-phenylxanthen-9-yl (Pixyl, Px) (10) or 4,4 -... 

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

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). ... 

Protection of S -hydroxyl groups of 2 -deoxyrlbonucleosides. The 9-phenyl-9-xanthyl (pixyl) derivatives of 2 -deoxyribonucleosides have better crystallization properties than the corresponding, usually used, dimethoxytrityl ethers, but also have similar acid lability, being removable in 8-15 minutes by 80% HOAc at 20°. 

C2-homologizati on of sugars with, 264-265 Acetamide, JV-bromo- (AcNHBr, NBA) bromohydrination with, 275-276, 287 Acetaminophen (= paracetamol), 301 Acetate, piperidinium cat. for aldol add., 82 —, sodium a-epimerization of ketones, 277 opening of oxiranes, 282 Acetic acid, anhydride (AcfO) protection with. See Protection Pummerer rearr. with, 51, 265 —, esters (See also Protection of hydroxy groups) C-H acidity, 10 1-methylethenyi ester pr., 174 transenolization, 58 —, bromo-, esters pr., 179 a2-synthon, 19, 65, 309 d2-synthon, 19, 301 —, chloro-, esters pr., 179 hydantoins from, 308 —, cyano-, esters pr., 177 pyrrolines from, 298 —, (dialkoxyphosphinyl)-, esters pr 188 Wittig-Horner olefinations, 267, 282 —, diazo-, ethyl ester pr, 176, 178 cyclopropanes from, 74—75 —, dichloro- deblocking of pixyl ethers, 342 —, hydroxy-, esters pr., 176 —, hydroxyphenyl-, (S)- (l-mandelic acid) ... 

Two intermediates (64 R=MMTr or pixyl) have been synthesised and used to make branched ribonucleic acids, since they permit extension in all three directions. 132 phosphoramidltes of type (65) have been prepared, where the base is also protected by a group removable by reductive cleavage. 133... 

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