Linkers p-alkoxybenzyl

In addition, a polymer-supported version of the intramolecular aglycon delivery was explored [148]. In this system, mannosyl thioglycoside 93 bound to polyethylene glycol (PEG) via a p-alkoxybenzyl linker was subjected to the two-step sequence and the resultant fi-manno-glycoside is specifically released into the non-polymeric phase, while most of the by-products remain bound to the polymer. 

Scheme 17.25 Attachment and of the p-alkoxybenzyl linker and subsequent cleavage.

In a related study, Lusinchi [11] reported the synthesis of a new soluble polymer containing a p-alkoxybenzyl alcohol linker, analogous to Wang resin. The polymer was utilized in intermolecular radical addition reactions. The polymer was synthesized by subjecting xanthate 65, formed in three steps from alcohol 63, to styrene polymerization in the presence of lauroyl peroxide... 

Amines derived from p-alkoxybenzyl-type linkers, despite not being acid cleav-able, still have synthetic utility. Anilines anchored to Wang resin, once converted into carboxamides or sulfonamides by reaction with the appropriate electrophile, can be cleaved with TFA (Figure 14.6) [34]. Sulfonamides of aliphatic amines may also be cleaved with TFA [36]. Stronger acids are generally required for acyl derivatives of amines but this can cause cleavage of the linker benzylic ether bond, leading to formation of p-hydroxybenzylated by-products. 

The addition of further o-methoxy groups to the p-alkoxybenzyl alcohol framework naturally results in linkers with enhanced acid sensitivities. One of the first linkers of this type was 2-(4-hydroxy-3-methoxyphenoxy)acetic acid (11) developed by Sheppard and colleagues for the Fmoc solid phase synthesis of protected peptide acids for fragment condensation [41]. Treatment of peptidyl resins with... 

To increase the stability of p-alkoxybenzyl resins to acids, Porco and Kusumoto introduced the p-acylaminobenzyl linker [68], which they found to be suitable for anchoring glycosides for oligosaccharide synthesis (Scheme 17.26). 

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