Photolabile protective groups

Piloto AM, Rovira D, Costa SPG, Gonfalves MST (2006) Oxobenzo[/]benzopyrans as new fluorescent photolabile protecting groups for the carboxylic function. Tetrahedron 62 ... 

Furuta, T., Wang, S. S. H., Dantzker, J. L., Dore, T. M., Bybee, W. J., Callaway, E. M., Denk, W. and Tsien, R. Y. (1999). Brominated 7-hydroxycoumarin-4-ylmethyls Photolabile protecting groups with biologically useful cross-sections for two photon photolysis. Proc. Natl. Acad. Sci. USA. 96, 1193-1200. 

Scheme 55 Photolabile protecting groups for alcohols and thiols.

In order to develop a material with these properties, the well-documented thermal characteristics of the aromatic polyamides were combined with the sensitivity of a photolabile protecting group. In 1973, Amit and Patchornik reported that N-substituted-ortho-nitroanilides are light-sensitive and undergo a photoinduced rearrangement to produce the corresponding carboxylic acid in excellent yield. (4)... 

The resolution of the photolithographic process determines the maximum achievable density of the array (i. e. the amount of sequence information encoded on the chip). Table 2 shows the relationship between the resolution, in terms of smallest feature size, and the maximum density at which an array can be printed . Application of the photolithographic process using photolabile protecting groups currently provides a spatial resolution that allows arrays to be fabricated with densities on the order of 106 sequences/cm2, which corresponds to an individual feature size of 10 X 10 m. This feature size is near the limit of resolution that can be achieved by this method using standard photolithography equipment. 

Heath et al. exploited photolithography to generate chemical patterns for the assembly of different nanocrystals (Fig. 13.10).72 Organic monolayers of an adsorbate functionalized with the photolabile protection group nitroveratryloxycarbonyl... 

One of the most common photochemical reaction pathways of carbonyl compounds is the formation of a diradicaloid excited state which is able to abstract a hydrogen atom at the y (or, more rarely, e) position, followed by either fragmentation or recombination. This process, which is known as the Norrish type II reaction, has a parallel in the photochemistry of nitro groups the intramolecular hydrogen abstraction of excited ortho-nitrotoluene is actually one of the very early synthetic photochemical transformations [9]. It has been exploited in a family of photolabile protecting groups, most prominent among which are derivatives of ortho-nitrobcnzyl alcohol, as introduced in 1966 by Barltrop et al. (Scheme 13.1) [10, 11],... 

The aldehyde side product can react with the freshly released amine, thus limiting the chemical yield. To avoid this reaction one can add an aldehyde scavenger, such as semicarbazide hydrochloride, hydrazine or an aldehyde scavenging resin (e.g., supported hydrazines). An alternative is to alter the structure of the photolabile protecting group. 

The photochemicaHy promoted rupture of a benzylic carbon-heteroatom bond is exploited in numerous photolabile protecting groups, for example in the 9-phenyl-xanthen-9-yl (also called pixyl group, X = O in Scheme 13.11) [40] and its sulfur-... 

Bochet, C.G. (2002) Photolabile protecting groups and linkers. Journal of the Chemical Society, Perkin Transactions 1, 125-142. 

Buehler, S., Lagoja, I., Giegrich, H., Stengele, K.-P. and Pfleiderer, W. (2004) New types of very efficient photolabile protecting groups based upon the [2-(2-nitrophenyl)propoxy]carbonyl (NPPOC)... 

Woell, D., Smirnova, J., Pfleiderer, W. and Steiner, U.E. (2006) Highly efficient photolabile protecting groups with intramolecular energy transfer. Angewandte Chemie, International Edition, 45, 2975-2978. 

Blanc, A. and Bochet, C.G. (2003) Bis(o-nitrophenyljethanediol A practical photolabile protecting group for ketones and aldehydes. Journal of Organic Chemistry, 68, 1138-1141. 

Aujard, I., Benbrahim, C., Gouget, M., Ruel, O., Baudin, F J.-B., Neveu, P. and Jullien, L. (2006) o-Nitrobenzyl photolabile protecting groups with red-shifted absorption syntheses and uncaging cross-sections for one- and two-photon excitation. Chemistry —A European Journal, 12, 6865-6879. 

Wang, P Hu, H. and Wang, Y. (2007) Application of the excited state meta effect in photolabile protecting group design. Organic Letters, 9, 2831-2833. 

Lin, W. and Lawrence, D.S. (2002) A strategy for the construction of caged diols using a photolabile protecting group. Journal of Organic Chemistry, 67, 2723-2726. 

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