Protecting moieties 4-methoxyphenyl

The chloro moiety of thieno[3,4-d]pyrimidine 383 was displaced by 4-(2-methoxyphenyl)piperazine or 4-(4-fluorobenzoyl)piperidine in refluxing propan-2-ol containing sodium bicarbonate and a catalytic amount of sodium iodide. The N-3 protecting group of the resulting derivatives 384 was... 

Use of the methoxyphenyl group as a latent P-ketoester represents the combined protection of two functional groups (ketone and ester) in a single moiety. It is very common to combine the protection of neighboring alcohol functions as henzylidene acetal, as an acetonide, or as a siladioxane (Scheme 7.12). Of these, the henzylidene acetals are most versatile, as they allow the selective deprotection of either the sterically more encumbered or less encumbered hydroxyl function [1,2]. 

The sugar moiety is blocked at C5 as a dimethoxytrityl [di(4-methoxyphenyl)phenylmethyl, DMT] ether, readily cleaved by mild acid through an SnI mechanism (Section 22-1 and Problem 40 of Chapter 22), much like 1,1-dimethylethyl (tcrt-butyl) ethers (Section 9-8, Real Life 9-2). To anchor the first protected nucleoside on the solid support, the C3 -OH is attached to an activated linker, a diester. Unlike the Merrifield medium of polystyrene, the solid used in oligonucleotide synthesis is surface-functionalized silica (Si02) bearing an amino substituent as a hook. Coupling to the anchor nucleoside is by amide formation. 

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