Synthesis and characterization of thiochromone S,S-dioxides as new photolabile protecting groups

3-Arylthiochromone derivatives were synthesized as new photolabile protecting groups, in which the photoreactivity was switchable based on oxidation of the sulfur atom (sulfide and sulfone); the protected substrates , released the corresponding alcohols, amines or carbonxylic acids almost quantitatively under UV-light in neutral condition and the photoproduct showed high fluorescence intensity.     

Sequential removal of photolabile protecting groups for carbonyls with controlled wavelength

A group of robust and easy-to-make photolabile protecting groups (PPGs) for carbonyl compounds has been developed. Sequential removal of different PPGs is achieved via control of irradiation wavelength.     

Oxazole light triggered protecting groups: synthesis and photolysis of fused heteroaromatic conjugates

Fused oxazole derivatives were synthesized and evaluated as new light triggered protecting groups by using amino acids as model bifunctional molecules. The photosensitivity of ester conjugates was tested under irradiation at 254, 300, and 350 nm. Oxazole conjugates were readily photolyzed with complete release of the amino acid, the best results obtained for naphtho[2,3-d]oxazole at 254 and 300 nm, being the first reported application of this type of heterocycles as photocleavable protecting groups for carboxylic acids.     

Oxobenzo[f]benzopyrans as new fluorescent photolabile protecting groups for the carboxylic function

The properties of three oxobenzo[f]benzopyrans as new fluorogenic photolabile protecting groups for the carboxylic function of amino acids were studied. Fluorescent amino acid conjugates were efficiently prepared and characterised. Photodeprotection of these compounds was carried out by irradiation at 300, 350 and 419 nm, the most suitable wavelength being 350 nm, on account of short irradiation times and good deprotection yields.     

Development of the 8-aza-3-bromo-7-hydroxycoumarin-4-ylmethyl group as a new entry of photolabile protecting groups

A significant substitution effect of the position of the bromo group on the photosensitivity of the 8-azacoumarin chromophore leads to the development of a highly photosensitive 8-aza-3-bromo-7-hydroxycoumarin-4-ylmethyl (aza-3-Bhc) group that shows excellent photolytic efficiency and hydrophilicity with long-wavelength absorption maxima. The newly identified aza-3-Bhc group can be applied to caged glutamates for ester-type and carbamate-type protections of carboxyl and amino functionalities.     

Kinetics of photochemical reactions of a new biphotochromic compound upon photolysis with light of different wavelengths

Using the method of microsecond flash photolysis with UV and visible light, the spectral and kinetic characteristics of intermediate products of photolysis in toluene and methanol solutions of a new biphotochromic compound have been studied, in which two photochromic moieties, spironaphthoxazine and azomethine, are linked to each other in such a way that there is conjugation between π-electronic systems of the moieties in the ground state of the molecule. Two intermediate products have detected, whose relative efficiency of formation substantially depends on the solvent and the wavelength of excitation light.     

Photoactivation of amino-substituted 1,4-benzoquinones for release of carboxylate and phenolate leaving groups using visible light

Upon exposure to visible light, 2-pyrrolidino-substituted 3,6-dimethyl-1,4-benzoquinones photocyclize to give benzoxazolines with quantum yields of 0.07-0.10 in CH2Cl2, 0.02-0.04 in CH3CN, and <0.01 in 30% aq CH3CN. With carboxylate or phenolate leaving groups incorporated via coupling to a 5-hydroxymethyl group of the quinones, the photocyclizations give benzoxazolines that eliminate the leaving groups in a dark reaction. Lifetimes for elimination of 4-YC6H4OH in 30% phosphate buffer in CD3CN (pD 7) at 17 degrees C are 13.1, 0.54, and 0.13 h for Y = H, CF3, and CN, respectively, and the linear equation log k (h(-1)) = 0.998(-pKa) + 8.80 gives a best fit to the data. Carboxylate leaving groups are rapidly eliminated upon photolysis of the quinones in aq CH3CN to produce an o-quinone methide intermediate that is trapped by 4 + 2 cycloaddition with unreacted starting material or with added 3-(dimethylamino)-5,5-dimethyl-2-cyclohexen-1-one. The ortho-quinone methide is observed at 339 and 455 nm by conventional absorption spectroscopy and gives a pseudo-first-order fit of the decay kinetics with tau1/2 = 34.9 min in 30% phosphate buffer in CH3CN at 20 degrees C.     

Application of benzyl protecting groups in the synthesis of prenylated aromatic compounds

Benzyl ethers have proven to be useful protecting groups for synthesis of phenols bearing isoprenoid chains because the benzyl groups can tolerate the conditions of halogen-metal exchange used to introduce the side chains yet are cleaved in good yields upon treatment with sodium s-butanol.     

Organogermanium compounds: First synthesis of bioactive trithiagermatranes substituted with novel functional groups

The synthesis and properties of trithiagermatranes (3) via reaction of tris(2-mercaptoethyl)amine with trimethoxygermyl adducts (5) and germanium sesquioxides (6) are described.     

A new protecting group for the exocyclic amino groups of nucleosides

A new protecting group has been developed for the exocyclic amino groups of nucleosides that occur in DNA. 3-Phenyl-[{N-(2-trimethylsilyl-ethoxycarbonyl)-2-amino}]-propanoic acid used as the protective agent.     

Overcoming the demons of protecting groups with amphoteric molecules

Synthetic organic chemists have long depended on protecting group manipulations when faced with the challenges of chemoselectivity and functional group incompatibility. Overcoming this dependence will improve the overall efficiency of chemical synthesis. By taking advantage of orthogonally reactive functional groups, amphoteric molecules can afford access not only to more efficient and strategic syntheses but also to the development of novel chemical transformations.     

Photodissociation of neutral argon clusters with visible laser light: new experimental evidence

Recently we have observed [1–4] photodissociation of neutral van der Waals clusters induced by visible laser light using coaxial interaction between the beams. Because of possible artifacts we have repeated here this experiment in a crossed beam configuration. The present results confirm the occurrence of this photodissociation effect. We suggest tentatively that excitation via Raman scattering is the origin of this phenomenon.     

Assessment of heat-sensitive thiophosphate protecting groups in the development of thermolytic DNA oligonucleotide prodrugs

Heat-sensitive thiophosphate protecting groups derived from the alcohol 4 or 10 have provided insights in the design of DNA oligonucleotide prodrugs. Indeed, functional groups stemming from the alcohol 9, 15, 16 or 22 may be applicable to thiophosphate protection of immunostimulatory CpG DNA motifs, whereas those originating from the alcohol 3, 5, 12, 13, 18, 20 or 22 offer adequate protection of terminal phosphodiester functions against ubiquitous exonucleases that may be found in biological environments. Functional groups derived from the alcohol 9, 15, 16, 19 or 23 are suitable for the protection of phosphodiester functions flanking the CpG motifs of immunomodulatory DNA sequences.     

Photochemical cyclization with release of carboxylic acids and phenol from pyrrolidino-substituted 1,4-benzoquinones using visible light

Visible light irradiation of 5-acyloxymethyl- and 5-phenoxymethyl-2-pyrrolidino-1,4-benzoquinones effects photoisomerization to labile oxazolidines, which undergo elimination of carboxylate or phenolate leaving groups in high yields to generate trappable o-quinone methide intermediates. [reaction: see text]     

A new reagent for the cleavage of NPS-amino protecting groups in peptide synthesis.

The value of several reagents capable of removing quantitatively the α-amino protecting group of NPS-aminoacyl- or peptidyl-derivatives is assessed, by comparison with the reagents currently used, i.e. hydrogen chloride, RS^–-nucleophiles or alkyl thioamides, especially with regard to reaction specificity and end-product solubility. New reagents proposed, 3-nitro-4-mercapto-benzoic acid, and its methyl ester, appear to optimize the numerous, and often competing, requirements. These were probed, under conditions suitable for both conventional and solid-phase methods, on a series of model compounds, including diversely protected amino acids and short peptides, as well as for the actual synthesis of a triacontapeptide by the stepwise, solid-phase approach.     

Toward a visible light mediated photocyclization: Cu-based sensitizers for the synthesis of [5]helicene

A photochemical synthesis of [5]helicene employing a copper-based sensitizer 7 has been developed that avoids the disadvantages associated with the traditional UV light mediated method. The visible light mediated synthesis uses common glassware and a simple household light bulb without the competing formation of [2 + 2] cycloadducts, regioisomers, or the overoxidation product benzo[ghi]perylene 3. Preliminary results show that the reaction time can be significantly reduced through the use of a continuous flow strategy.     

A new visible light sensitive photoinitiator system for the cationic polymerization of epoxides

This communication reports the development of an efficient three‐component visible light sensitive photoinitiator system for the cationic ring‐opening photopolymerization of epoxide monomers and epoxide functional oligomers. The photoinitiator system consists of camphorquinone in combination with a benzyl alcohol to generate free radicals by the absorption of visible light. Subsequently, the radicals participate in the free radical chain induced decomposition of a diaryliodonium salt. The resulting strong Brønsted acid derived from this process catalyzes the cationic ring‐opening polymerization of a variety of epoxide substrates. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 866–875, 2009