Protecting groups light-sensitive

Miscellaneous. The reaction products of sahcylaldehyde with certain compounds containing active methylene groups, eg, acetylacetone, are excellent uv absorbers. Films containing these compounds can be used as uv filters to protect light-sensitive foods, wood products, paper, dyes, fibers, and plastics (95). 

Soares AMS, Costa SPG, Gonfalves MST (2010) 2-Oxo-2//-benzol/i bcnzopyran as a new light sensitive protecting group for neurotransmitter amino acids. Amino Acids, doi 10.1007/ s00726-009-0383-z... 

TRITC is relatively insoluble in water, but it can be dissolved in DMF or DMSO as a concentrated stock solution prior to its addition to an aqueous reaction mixture. The isothiocyanate group is reasonably stable in aqueous solution for short periods, but will degrade by hydrolysis. TRITC also is more stable to photobleaching than FITC (Section 1, this chapter), and its absorption and emission spectra are less sensitive to environmental conditions, such as plT. It is best, however, to use only fresh reagent for modification purposes. Storage should be done under desiccated conditions, protected from light, and at -20°C. 

The protection of alcohols by conversion into light-sensitive ethers is most attractive. Initially, the preparation of 2-nitrobenzyl (nBn) ethers presented a problem, although their potential usefulness as protecting groups, stable under a variety of reaction conditions, that nevertheless are readily photolyzed at >320 nm (see Scheme 2) was recognized immediately. 

The protection of amino groups of amino sugars benefits particularly from the use of new blocking groups introduced for peptide synthesis. In this context, light-sensitive urethans and amides that can be utilized for the protection of amino groups in amino sugars are of particular interest in saccharide synthesis and modification. 

Ester formation is the main and most efficient means of protecting carboxylic acids. The protection of a carboxylic acid as an amide is infrequent, as its removal normally requires drastic conditions. Most of the work concerned with the use of light-sensitive protecting-groups for carboxylic acids is in peptide synthesis. Carboxylic acids are protected as photosensitive esters, including ester linkages to polymer supports or as (difficult to prepare) photosensitive amides. Many of these techniques may be readily applied to sugar acids. 

The photosolvolysis of 3-nitrophenyl esters is the first example of the use of a light-sensitive protecting-group that has appeared in the literature. 3-Nitrophenyl and the more-sensitive 3,5-dinitrophenyl phosphoric esters undergo photohydrolysis (mercury lamp) to a phosphoric derivative and the corresponding nitrophenol an example of a synthetic application is presented in Scheme 30. 

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 development of light-sensitive protective groups began in the early 1960s [129-131] and led to the identification of several functionalities that could be selectively cleaved under UV irradiation (for a review, see [132]). Some of these protective groups, such as 2-nitrobenzyl esters, carbonates, or carbamates [131,133-135], benzoin [136-139], and other phenacyl esters [140] were also found to be useful as photocleavable linkers. 

Rubinstein, M., Amit, B. and Patchornik, A. (1975) Use of a light-sensitive phosphate protecting group for mononucleotide syntheses. Tetrahedron Letters, 16, 1445-1448. 

Scheme 1) (Kessler et ah. Chapter 6). The system is based on a tert-hutyl ketone-derived linker, which is sensitive to 305 nm light, and a nitroverat-ryloxycarbonyl group (36) (sensitive at 360 nm) as the carboxyl protecting group. Scheme 1 illustrates the method for the synthesis of Leu-Enkephalin (in 55% overall yield) from tethered and protected leucine. 

In this case the protective effect is probably also due to inhibition of the auto-oxidation during thermal processing of the polymer. This auto-oxi-dation could otherwise result in the formation of light-sensitive carbonyl groups. 

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