The photolabile 3'-O-{[2-(2-nitrophenyl)propoxy]carbonyl}-protected 5'-phosphoramidites (16 ± 18) were synthesized (see Scheme) for an alternative mode of light-directed production of oligonucleotide arrays. Because of the characteristics of these monomeric building blocks, photolithographic in situ DNA synthesis occurred in 5' 3 3' direction, in agreement with the orientation of enzymatic synthesis. Synthesis yields were as good as those of conventional reactions. The resulting oligonucleotides are attached to the surface via their 5'termini, while the 3'-hydroxy groups are available as substrates for enzymatic reactions such as primer extension upon hybridization of a DNA template (see Fig. ). The production of such oligonucleotide chips adds new procedural avenues to the growing number of applications of DNA microarrays.
Helvetica Chimica Acta ± Vol. 84 ( ) 2090 Scheme. Synthesis of Solid Phase 5'-O-Phosphoramidites Bearing Photolabile 3'-O-nppoc Groups DMTr (MeO) 2 Tr 4,4'-dimethoxytrityl, tac [4-(tert-butyl)phenoxy]acetyl a) 1.2 Equiv. of 3-{[2-(2-nitrophenyl)propoxy]carbonyl}-1-methyl-1H-imidazolium chloride (2) (from 1methyl-1H-imidazole and 2-NO 2 ÀC 6 H 4 ÀCH(Me)CH 2 OCOCl (1)). b) 10% CCl 3 COOH. c) 2-Cyanoethyl tetraisopropylphosphorodiamidite, pyridine hydrochloride.