More Efficient Photolithographic Synthesis of DNA-Chips by Photosensitization

Abstract

Light-induced release of photolabile protecting groups is a key step in the photolithographic in-situ synthesis of oligonucleotides in the production of high-density DNA-chips. [1,2] Protecting groups of the o-nitrophenyl type that are preferentially used for this purpose have rather low absorption coefficients at 366 nm, the wavelength of the most conveniently used mercury line. The weak absorptivity of these compounds leads to principal limitations of their light sensitivity. Since they have photoreactive triplet states, however, this problem can be overcome by introducing a triplet sensitizer that efficiently absorbs the light and transfers the electronic energy to the reactive protecting group.The sensitized photodeprotection was studied in detail for the o-nitrophenyl-2-propoxycarbonyl (NPPOC) group [3] where the photo cleavage occurs via b-elimination of the corresponding nitrostyrene derivative as shown in the scheme. The first step of this reaction is photochemically initiated intramolecular H-atom transfer from the a-position to the nitro group whereby an aci-nitro compound is formed [3] . Protolytic dissociation of the aci-nitro compound is followed by the b-elimination from the aci-nitro anion. As an example of the time-resolved

Development of Trityl-Based Photolabile Hydroxyl Protecting Groups

“…Photolabile protecting groups (PPGs) are unique and useful protecting groups not only in organic chemistry but also in biochemistry, photolithography, and material science. − Their advantages stem from using light as a traceless reagent in the removal process. Photochemical removal of protecting groups often occurs under mild conditions and does not require chemical reagents.…”

Photolabile Protecting Groups Based on the Excited State Meta Effect: Development and Application†

“…Light-promoted chemical reactions are important to many applications because (a) light is a traceless reagent, and (b) photoreactions can take place under ambient conditions with precise spatial and temporal control. One important application of organic photochemistry is in the development of photolabile protecting groups (PPGs), which are indispensable tools in organic chemistry (1)(2)(3)(4)(5)(6), biochemistry and biology (3,(7)(8)(9)(10), polymer chemistry (11), surface patterning (12)(13)(14)(15) and photolithography (2,4,16). The past several decades have witnessed significant progress of utilizing PPGs in the basic and applied research, and new PPGs and their creative applications have emerged at an unprecedented pace.…”

The α,5‐Dicarboxy‐2‐nitrobenzyl Caging Group, a Tool for Biophysical Applications with Improved Hydrophilicity: Synthesis, Photochemical Properties and Biological Characterization

“…In contrast to conventional mixing techniques the use of caged compounds allows kinetic investigations on a microsecond time scale on cell surfaces (8–14) or within cells (15–17). Since then various kinds of caging groups have been introduced (18–39). However, the o ‐nitrobenzyl protecting group and its numerous derivatives are still the most widely used ones.…”