Benzyl esters, as protecting groups

Putting on the phosphate is tricky too and more protection is necessary. This phosphorus compound with one chloride as leaving group and two benzyl esters as protecting groups proved ideal. The benzyl esters can be removed by hydrogenation (Chapter 24) and the acetal by treatment with dilute acid to give AMP. 

As discussed above, each linker family is sensitive toward a certain spectrum of cleavage conditions and is therefore stable to dissimilar conditions. Since most of the linkers are based on well-established protecting groups, table 6.1.2 can be used for the determination of orthogonality. For example, benzyl-type linkers, most of which are cleaved by electrophiles, and are stable towards nucleophiles, can be combined with ester-based protective groups. 

AUcyl esters (e.g., methyl, ethyl, benzyl esters) are usually stable toward amines and, thus, are used as protecting groups. Some anecdotic examples of amide bond formation with aUcyl esters, however, are reported in the literature. High reaction temperature, addition of a Lewis acid (52), or use of organoaluminium species generated from DIBAL-H-H2NR (53) can enable these reactions. Saturated ammonia in methanol can also react with... 

Naphthylmethyl and 2-naphthylmethyl esters have been proposed as protecting groups as they are selectively cleaved in the presence of a benzyl ester by homogeneous palladium-catalyzed hydrogenolysis using ammonium formate.P ... 

The ether and ester derivatives of benzyl alcohols are widely utilized as protecting groups. In the case of protected peptides hydrogenolysis often has advantages over hydrolysis. This conversion is use-... 

The use of a phenolic ester as anchoring group limits the choice of the protective groups. An appropriate choice is tert-butyloxy-carbonyl (Boc, trifluoroacetic acid cleavable) for N -blocking of the amino acid esterified with the phenol and functionalized benzyl groups for side-chain functions. An alternative (preferred in many applications) is tert-butyl derived side-chain blocking groups and 2-p-biphenylyl-2-propyloxycarbonyl (Bpoc) for N -protection. ... 

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