Photolabilization

Lewis J W, Warner J, Einterz C M and Kliger D S 1987 Noise reduction in laser photolysis studies of photolabile samples using an optical multichannel analyzer Rev. Sol. Instrum. 58 945-9... 

Another interesting variation on the linkage holding together two benzocrowns was reported by Shinkai and coworkers In their case, the benzo groups on the crowns were also part of a photolabile azobenzene system. The azo-linked bis-crown was prepared as follows (see Eq. 3.34). 4 -Nitrobenzo-l 5-crown-5 was reductively dimerized... 

Zn powder, KOH) to give the trans-azolinked crown (mp 187—188°) in unspecified yield. The crown proved to be photolabile, undergoing facile trans-cis isomerism upon irradiation. 

Dehydrotestosterone acetate (174) in nonprotic solvents (dioxane, benzene) undergoes a rearrangement to the isomer (175). This product is photolabile and isomerizes readily to new cross-conjugated dienones. Thus, ultraviolet irradiation of (174), its 1-, 2- and 4-methyl homologs, and its lOa-stereoisomer (188) in dioxane solution causes, in each case, a series of rearrangements as summarized on page 331 for (174) and (188). ... 

A Wild and Woolly Photolabile Fluorescent Ester, 195 A/-Phenylcarbamate, 195 Borate, 196... 

Chen, F.-Q., et al. (1994). Synthesis and preliminary chemi- and bioluminescence studies of a novel photolabile coelenterazine analogue with a trifluoromethyl diazirine group. Chem. Commun. 2405-2406. 

In another study exposure of water containing NDEA to sunlight caused a raoid decrease in the NDEA concentration (to near zero after 16 h)2Q. Wolfe, et al. 2fi found Ji-nitrosoatrazine to be photolabile in natural water with both denitrosation and dealkylation being identified as decomposition pathways. 

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. 

Photolabile linkers play an important role in solid-phase organic synthesis (SPOS) due to their stability under both acidic and basic conditions. The ONb photolabile linker was modified to improve cleavage rates and yields Fmoc-Tos-OFI was released in 87% yield after 23 h (Scheme 4) [24]. Specifically, the primary alcohol was changed to a secondary benzylic alcohol and the attachment to the resin was through an alkyl chain as opposed to an amide function. Linker 20 was used for the production of carboxylic acids or carbohydrates. A second example... 

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. 

Peukert S, Giese B. The pivaloyglycol anchor group A new platform for a photolabile linker in solid-phase synthesis. J Org Chem 1998 63 ... 

Ajayaghosh A, Pillai YNR. Solid-phase synthesis and C-terminal amidation of peptides using a photolabile o-nitrobenzhydrylaminopolystyrene support. Tetrahedron Lett 1995 36 777-780. 

Holmes CP, Jones DG. Reagents for combinatorial organic synthesis Development of a new o-nitrobenzyl photolabile linker for solid-phase synthesis. J Org Chem 1995 60 2318-2319. 

Some drugs are intrinsically photolabile examples include tubocurarine and chlorpromazine, each of which has been used to label the binding regions of receptors. 

The initially formed cyclopropyl ketones from the photolysis of cross-conjugated cyclohexadienones are also photolabile. Usually the photochemical rearrangements of cyclopropyl ketones involve cleavage of the cyclopropyl bond which forms part of the cyclopentenone ring followed by either (a) a substituent migration or (b) rearrangement through a spiro intermediate. While the literature in this area is too voluminous to review in... 

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

Some quinolizinium derivatives such as MPB-07 60 have importance as chloride channel activators. This compound has been shown to be photolabile in aqueous solution when exposed to daylight, being transformed into the phenolic derivative 62 with the deprotonated form 61 as an intermediate, as shown in Scheme 1 <2002JPS324>. A highly regioselective solid-state photodimerization of naphthoquinolizinium salts has also been described <2002EJO2624>. 

Despite the considerable amount of information that has been garnered from more traditional methods of study it is clearly desirable to be able to generate, spectroscopically characterize and follow the reaction kinetics of coordinatively unsaturated species in real time. Since desired timescales for reaction will typically be in the microsecond to sub-microsecond range, a system with a rapid time response will be required. Transient absorption systems employing a visible or UV probe which meet this criterion have been developed and have provided valuable information for metal carbonyl systems [14,15,27]. However, since metal carbonyls are extremely photolabile and their UV-visible absorption spectra are not very structure sensitive, the preferred choice for a spectroscopic probe is time resolved infrared spectroscopy. Unfortunately, infrared detectors are enormously less sensitive and significantly slower... 

Methyl-Cobalamine and Related Compounds. There are three major types of cobalamine in animals and man, the methyl and hydroxo derivatives and the deoxyadenosyl derivative (coenzyme B12). The unique metal-carbon bond in the methyl derivative and in B12 is extremely photolabile, and their photolyses have been widely studied. However, radiolytic processes have not been widely studied. 

Spatial electrochromism has been demonstrated in metallopolymeric films.28 Photolysis of poly-[Run(L10)2(py)2]Cl2 thin films on ITO glass in the presence of chloride ions leads to photochemical loss of the photolabile pyridine ligands, and sequential formation of po/y-[RuII(Llt))2(py)Cl]Cl and po/y-[Run(L10)2Cl2] (Scheme 1). 

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. 

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