Photolysis, linker, solid-phase synthesis

There are a number of examples of benzoin and substituted benzoin esters that have been employed as photoremovable protecting groups for carboxylic acids. Among these, the application of benzoin as a traceless linker for solid-phase synthesis of oligopeptides and introduction of Fmoc-protected amino acids by Balasubramanian ° is instructive. As an example, the release of Fmoc-Ala shown in Eq. 69.21 occurs upon photolysis at 350. Balasubramanian found that the maximum yield was obtained after a 2-h photolysis as determined by HPLC (Eq. (69.21). 

Scheme 6.192 shows the o-nitrobenzyl moiety used as a photolabile linker in the solid-phase oligosaccharide synthesis on a polystyrene (PS) support.1208 After the synthesis of the protected oligosaccharide 404, PS attached to the photoremovable group is removed by photolysis and the final product is obtained by hydrogenolysis. Such a strategy could be promising for combinatorial synthesis of oligosaccharide libraries. 

They reported a soUd phase synthesis with spermine or polyethyleneimines (PEI, 600 MW) tethered via o-nitrobenzyl linkages to polyethylene oxide beads (ArgoGel-NH2 Schemes). The photolysis of 0-2-nitrophenylethyl 0, 0"-diethyl phosphate or sohd phase with o-nitrobenzyl group as synthetic linker was completely degradable after photoirradiation at 365 nm for 10-18 min at 3.5 mW cm. With this linker system DNA-loaded solid phase is assumed to be exploited for spatially, temporally, or dose-controlled release of DNA-polyamine complexes, at extracellular or intracellular sites [207]. 

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