Protecting photolabile

Various UV absorbers have been used to protect photolabile solutions of drugs. p-Aminobenzoic acid absorbs UV radiation in the 360 to 313 nm UV region. Evidence of its photoprotective ability has been reported for solutions of colchicine (70), tetracycline hydrochloride (71), doxorubicin hydrochloride (77), and reserpine (106). 

As described in the previous sections, plastic and glass containers used for the production of parenterals offer little or no protection against optical irradiation (Figure 14.1). It is therefore important to protect photolabile products from sunlight and artificial light sources by using an outer, nontransparent container or a colored outer bag, or wrapping with aluminum foil. 

Kulikov, A. Arumugam, S. Popik, V. V. Photolabile protection of alcohols, phenols, and carboxylic acids with 3-hydroxy-2-naphthalenemethanol. J. Org. Chem. 2008. 73, 7611-7615. 

Routledge A, Abell C, Balasubramanian S. The use of a dithiane-protected benzoin photolabile safety catch linker for solid-phase synthesis. Tetrahedron Lett 1997 38 1227-1230. 

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 adopted plan follows the different types of photochemical reactions [substitutions, additions, rearrangements, reduction, oxidation, photolabile protections] with the presentation of some typical synthetic examples and of some mechanistic aspects. 

A class of photolabile linkers has been developed to circumvent the use of silyl ethers as linkers and allow for the use of temporary silyl protecting groups.34,35 Photolabile linkers, such as 2, often involve the use of o-nitrobenzyl ether groups. This functional group is stable to a variety of conditions however, cleavage from the polymer support is often slow and... 

Fig. i Matrix isolation method of surface immobilization of probe oligonucleotide/poly-electrolyte mixed film for enhanced selectivity. Phase 1 Photolabile dimethoxybenzoin (DMB) protecting groups are selectively exposed to electromagnetic radiation of appropriate wavelength to provide reactive sites in which polyelectrolyte spacers can be immobilized. Phase 2 The remaining DMB-protected sites are photo-deprotected to expose sites for probe oligonucleotide immobilization onto the solid surface... 

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. 

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