| Abstract
| - New methods based on photolithography and surface fluorescencewere used to determine photodeprotectionrates and stepwise yields for light-directed oligonucleotide synthesisusing photolabile 5‘-(((α-methyl-2-nitropiperonyl)oxy)carbonyl)(MeNPOC)-2‘-deoxynucleoside phosphoramidites onplanar glass substrates. Under near-UV illumination (primarily 365 nm) from a mercury light source, the rate ofphotoremoval of the MeNPOC protecting group wasfound to be independent of both the nucleotide and length of thegrowing oligomer (t1/2 = 12 s at 27.5mW/cm2).A moderate dependence on solvent polarity was observed, withphotolysis proceeding most rapidly in the presenceof nonpolar solvents or in the absence of solvent (e.g.,t1/2 = 10−13 s at 27.5mW/cm2). In solution, the photolysisrate was linearly dependent on light intensity over the range 5−50mW/cm2. Average stepwise yields for thesynthesisof dodecamer oligonucleotides were in the range of 92−94%, usingmonomers based onN6-(phenoxyacetyl)-2‘-deoxyadenosine, N2-isobutyryl-2‘-deoxyguanosine,N4-isobutyryl-2‘-deoxycytidine, and thymidine.By comparison,an efficiency of 98%/step was obtained using a conventional5‘-dimethoxytrityl monomer with acid deprotection onthe same support. The lower yields associated with thephotochemical process appears to be due to incompleterecovery of free 5‘-hydroxyl groups after photolysis on the support,although high yields of 5‘-OH nucleosides (≥96%)are consistently observed when 5‘-MeNPOC monomers are photolyzed insolution.
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