Nucleotide. XIV. Substituierte β‐Phenyläthyl‐Gruppen. Neue Schutzgruppen für Oligonucleotid‐Synthesen nach dem Phosphorsäuretriester‐Verfahren

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Abstract
XIV. Substituted β‐Phenyl‐ethyl Groups. New Blocking Groups for Oligonucleotide Syntheses by the Phosphotriester ApproachVarious o‐ and p‐substituted β‐phenylethanols (2–10) have been synthesized and investigated as blocking groups in the phosphotriester approach. A large number of 5′‐O‐tritylated thymidine‐3′‐phosphotriesters (13–36) with two different phosphate protecting groups have been prepared, characterized, and studied according to their chemical stability and usefullness for oligonucleotide syntheses. The combination of a 5′‐O‐monomethoxytrityl‐ and a 3′‐(2,5‐dichlorophenyl, p‐nitrophenylethyl)‐phosphate function as in 18 turned out to possess optimal properties as a monomeric nucleotide building block due to the fact that these blocking groups can be quantitatively and selectively be removed without harming each other by trifluoroacetic acid in chloroform to 41, by oximate to 42, and by DBU to 43. The base‐catalyzed removal of the monosubstituted phenylethyl groups by DBU or DBN respectively as well as the disubstituted phenylethyl groups by triethylamine in aprotic solvents is a β‐elimination process leading to phosphodiesters without attack on the P‐center.