A protecting group for carboxylic acids that can be photolyzed by visible light

We report on a photolabile protecting (caging) group that is new for carboxylic acids. Unlike previously used caging groups for carboxylic acids, it can be photolyzed rapidly and efficiently in the visible wavelength region. The caging group 7-N,N-diethyl aminocoumarin (DECM) was used to cage the gamma-carboxyl group of glutamic acid, which is also a neurotransmitter. The caged compound has a major absorption band with a maximum at 390 nm (epsilon(390) = 13651 M(-)(1) cm(-)(1)). Experiments are performed at 400 nm (epsilon(400) = 12232 M(-)(1) cm(-)(1)) and longer wavelengths. DECM-caged glutamate is water soluble and stable at pH 7.4 and 22 degrees C. It photolyzes rapidly in aqueous solution to release glutamic acid within 3 micros with a quantum yield of 0.11 +/- 0.008 in the visible region. In whole-cell current-recording experiments, using HEK-293 cells expressing glutamate receptors and visible light for photolysis, DECM-caged glutamate and its photolytic byproducts were found to be biologically inert. Neurotransmitter receptors that are activated by various carboxyl-group-containing compounds play a central role in signal transmission between approximately 10(12) neurons of the nervous system. Caged neurotransmitters have become an essential tool in transient kinetic investigations of the mechanism of action of neurotransmitter receptors. Previously uncaging the compounds suitable for transient kinetic investigations required ultraviolet light and expensive lasers, and, therefore, special precautions. The availability of caged neurotransmitters suitable for transient kinetic investigations that can be photolyzed by visible light allows the use of simple-to-use, readily available inexpensive light sources, thereby opening up this important field to an increasing number of investigators.     

2,5-Dimethylphenacyl carbonates: a photoremovable protecting group for alcohols and phenols.

Synthesis and photochemistry of a photochemically removable protecting group for alcohols and phenols, based on the 2,5-dimethylphenacyl (DMP) chromophore, is described. DMP carbonates release the corresponding hydroxy group containing molecules in high isolated yields (>70%), with quantum yields Phi= 0.1-0.2 in methanol and Phi= 0.36-0.51 in cyclohexane. The reactions proceed predominantly by the triplet pathway via E-photoenols, the lifetimes of which of approximately 2 s or 3 ms in cyclohexane or methanol, respectively, were determined by laser flash photolysis.     

Design of xanthone propionate photolabile protecting group releasing acyclovir for the treatment of ocular herpes simplex virus

We have attached the antiviral drug acyclovir (ACV) to a xanthone photolabile protecting group (or photocage) through the O6 position of acyclovir, a procedure designed for the treatment of ocular herpes simplex virus infections. Acyclovir is photoreleased from the photocage, under physiological conditions, with a quantum yield (Φ(ACV?release)) of 0.1-0.3 and an uncaging cross section (Φ·ε) of 450-1350 M cm(-1). We demonstrate that this photorelease method outcompetes alternative reaction pathways, such as protonation. Furthermore, complete release of the drug is theoretically possible given a sufficient dose of light . Surprisingly the acyclovir photocage, also showed some antiviral activity towards HSV-1.     

N-acyl-N-carboxymethyl-2-nitroaniline and its analogues: a new class of water-soluble photolabile precursor of carboxylic acids

The synthesis and photochemistry of a new class of water-soluble, photolabile protecting group, the N-carboxymethyl-2-nitroanilinyl (CNA) group, are described. All three CNA-caging compounds synthesized underwent clean photochemical reaction in aqueous buffer solution to produce the intended product of acetic acid, along with the corresponding nitroso aromatic.     

Using photolabile protecting groups for the controlled release of bioactive volatiles

To develop their biological activity, bioactive volatile compounds, such as pheromones or fragrances, have to evaporate from surfaces. Because these surfaces are usually exposed to natural daylight, the preparation of non-volatile precursors using photoremovable protecting groups is an ideal tool to control the release of caged volatile molecules from various surfaces by light-induced covalent bond cleavage. Many photoreactions occur under mild environmental conditions and are highly selective. To break covalent bonds under typical application conditions, the photoreaction has to proceed at ambient daylight, to tolerate the presence of oxygen and to run in polar media (e.g. in water). The amount of volatiles generated from photochemical delivery systems depends on the light intensity to which the systems are exposed. Both photoisomerisations and photofragmentations have successfully been investigated for the slow release of caged pheromones and fragrances from their corresponding precursors.     

Oxidation of substituted benzyl alcohols to carboxylic acids by Nocardia corallina B-276

Whole cells of Nocardia corallina B-276, oxidized 21 substituted benzyl alcohols, at 1 mM scale, to carboxylic acids at 28-30°C, giving yields of products from 5 to 77%.     

Water-soluble o-hydroxycinnamate as an efficient photoremovable protecting group of alcohols with fluorescence reporting

Two new o-hydroxycinnamates have been prepared for photoremovable protecting groups, and their photochemistry has been investigated. The photolysis of two caged compounds can efficiently release the corresponding alcohol in aqueous solutions, and the uncaging reaction proceeds with large one-photon excitation cross sections (1919 and 1535 M(-1) cm(-1)). The uncaging process has been observed by NMR spectroscopy. The caged compounds exhibit good aqueous solubility and excellent resistance to hydrolysis in a buffer solution.     

2,5-Dimethylphenacyl carbamate: a photoremovable protecting group for amines and amino acids.

2,5-Dimethylphenacyl (DMP) carbamates (1a-c) released the corresponding free amines or amino acids in high chemical yields, albeit with quantum yields Phi of only 0.04-0.09, upon irradiation in either aprotic or protic solvents. The photoreaction proceeded principally from the triplet excited state via the E-photoenol. The lifetimes of the triplet enol and the E- and Z-enols in the ground state were determined by laser flash photolysis. The primary photoinitiated transformation liberated a carbamic acid derivative, which subsequently decarboxylated to the amino group-containing compound. Exhaustive irradiation of a DMP-protected aniline (1a) in acetonitrile did not provide aniline in quantitative chemical yields, because it was involved in reductive cleavage of the starting material as an electron donor, thereby decreasing the overall deprotection yield (86%). Phenylalanine methyl ester, liberated from 1c, was, however, obtained in excellent chemical yield (97%). It was also found that the carbamates, while thermally stable, released amines with higher quantum yields in acidic methanol solutions. The DMP chromophore is proposed as an excellent photoremovable protecting group for amino acids and, under specific conditions, for amines in organic synthesis and biochemistry.     

Enantioselective recognition of carboxylic acids by novel fluorescent triazine‐based thiazoles

Hydrogen bonding and π‐π interactions take special part in the enantioselectivity task. In this regard, because of having both hydrogen acceptor and hydrogen donor groups, melamine derivatives become more of an issue for enantioselectivity. In the light of such information, triazine‐based chiral, fluorescence active novel thiazole derivatives L1 and L2 were designed and synthesized from (S)‐(?)‐2‐amino‐1‐butanol and (1S,2R)‐(+)‐2‐amino‐1,2‐diphenylethanol. The structural establishment of these compounds was made by spectroscopic methods such as FTIR, ¹H, and ¹³C NMR. While the solution of these compounds in DMSO did not show any fluorescence emission, it was observed that the emission increased 44‐fold for L1 and 55‐fold for L2 in 95% water, similar to the aggregation‐induced emission (AIE) characterized compounds. In this regard, enantioselective capabilities of these compounds against carboxylic acids were tested, and in experiments carried out at a ratio of 40/60 DMSO/H₂O, it was determined that R‐2ClMA increased the fluorescence emission of L1 chiral receptor by 2.59 times compared to S‐isomer.     

Use of water-soluble 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide for the fluorescent determination of uronic acids and carboxylic acids

Reaction between glucuronic acid and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) was monitored by the o-phthalaldehyde (OPA) method, which was developed for the fluorescent assay of compounds containing an amino group. About 1 nmol of glucuronic acid was detected by this method. This EDC-OPA method was effective in detecting not only acidic sugar but also carboxylic acid. Although the sensitivity of the EDC-OPA method was somewhat lower than that of amino acid determination by OPA, a very simple and convenient assay was attained for compounds containing a carboxyl group.     

Biocatalytic reduction of short‐chain carboxylic acids into their corresponding alcohols with syngas fermentation

Short‐chain carboxylic acids generated by various mixed‐ or pure‐culture fermentation processes have been considered valuable precursors for production of bioalcohols. While conversion of carboxylic acids into alcohols is routinely performed with catalytic hydrogenation or with strong chemical reducing agents, here, a biological conversion route was explored. The potential of carboxydotrophic bacteria, such as Clostridium ljungdahlii and Clostridium ragsdalei, as biocatalysts for conversion of short‐chain carboxylic acids into alcohols, using syngas as a source of electrons and energy is demonstrated. Acetic acid, propionic acid, n‐butyric acid, isobutyric acid, n‐valeric acid, and n‐caproic acid were converted into their corresponding alcohols. Furthermore, biomass yields and fermentation stoichiometry from the experimental data were modeled to determine how much metabolic energy C. ljungdahlii generated during syngas fermentation. An ATP yield of 0.4–0.5 mol of ATP per mol CO consumed was calculated in the presence of hydrogen. The ratio of protons pumped across the cell membrane versus electrons transferred from ferredoxin to NAD⁺ via the Rnf complex is suggested to be 1.0. Based on these results, we provide suggestions how n‐butyric acid to n‐butanol conversion via syngas fermentation can be further improved. Biotechnol. Bioeng. 2013; 110: 1066–1077. © 2012 Wiley Periodicals, Inc.     

Deprotonated carboxylic group of amino acids transforms adenine into its rare prototropic tautomers

By UV spectroscopic data for anhydrous DMSO solutions and ab initio HF/6-31G** calculations in vacuum it was shown for the first time that deprotonated amino acid carboxylic group is able to change tautomeric state of a nucleotide base, exactly to convert the N9H ground-state prototropic tautomer of adenine into the N7H and N1H rare ones.     

Synthesis of fluorescent, photolabile 3'-O-protected nucleoside triphosphates for the base addition sequencing scheme

The dansylated nucleoside triphosphates 1a and 1b were prepared as a prelude to investigating sequencing of DNA via a scheme that does not involve electrophoresis.     

Synthesis and characterization of novel biodegradable poly(carbonate ester)s with photolabile protecting groups

Novel biodegradable poly(carbonate ester)s with photolabile protecting groups were synthesized by ring-opening copolymerization of L-lactide (LA) with 5-methyl-5-(2-nitro-benzoxycarbonyl)-1,3-dioxan-2-one (MNC) with diethyl zinc (Et2Zn) as catalyst. The poly(L-lactide-co-5-methyl-5-carboxyl-1,3-dioxan-2-one) (P(LA-co-MCC)) was obtained by UV irradiation of poly(L-lactide acid-co-5-methyl-5-(2-nitro-benzoxycarbonyl)-1,3-dioxan-2-one) (P(LA-co-MNC)) to remove the protective 2-nitrobenzyl group. The free carboxyl groups on the copolymers P(LA-co-MCC) were reacted with paclitaxel, a common antitumor drug. Gel permeation chromatography and NMR studies confirmed the copolymer structures and successful attachment of paclitaxel to the copolymer.     

2-Oxo-2H-benzo[h]benzopyran as a new light sensitive protecting group for neurotransmitter amino acids

Aiming at the development of new benzopyran-based photocleavable protecting groups, novel chloromethylated and hydroxymethylated 2-oxo-2H-benzo[h]benzopyran derivatives bearing a methoxy substituent were designed and used in the synthesis of a series of fluorescent bioconjugates, by linking through an ester or urethane bond to several model neurotransmitter amino acids (glycine, alanine, β-alanine and γ-aminobutyric acid, GABA). The resulting fluorescent bioconjugates with emission in the visible range and high fluorescent quantum yields, were subjected to photocleavage reaction in methanol/HEPES buffer (80:20) solution at different wavelengths of irradiation (250, 300, 350 and 419 nm) and photocleavage kinetic data were obtained.     

Olfactory sensitivity for carboxylic acids in spider monkeys and pigtail macaques

Using a conditioning paradigm, the olfactory sensitivity of four spider monkeys and four pigtail macaques for a homologous series of carboxylic acids (n-propionic acid to n-heptanoic acid) was investigated. With only few exceptions, the animals of both species significantly discriminated concentrations <1 p.p.m. from the odorless solvent and in several cases individual monkeys even demonstrated thresholds <1 p.p.b. The results showed (i). both primate species to have a well-developed olfactory sensitivity for carboxylic acids, which for some substances matches or even is markedly better than that of species such as the rat or the dog and (ii). a significant correlation between perceptibility in terms of olfactory detection thresholds and carbon chain length of the carboxylic acids in both species tested. These findings lend further support to the growing body of evidence suggesting that between-species comparisons of the number of functional olfactory receptor genes or of neuroanatomical features are poor predictors of olfactory performance, and that general labels such as 'microsmat' or 'macrosmat'-which usually are based on allometric comparisons of olfactory brain structures-are inadequate to describe a species' olfactory capabilities.     

Mitochondrial permeability for alcohols,aldoses, and amino acids

Summary Mitochondria isolated from potato tubers were placed in solutions containing various alcohols, aldoses, or neutral amino acids. Based on the osmotic responses in the different media, the reflection coefficients and hence the relative permeabilities of the nonelectrolytes could be determined. The reflection coefficients ( _j 'S) of the potato tuber mitochondria for alcohols became progressively larger as hydroxymethyl groups were added to the molecule,viz. methanol ( _j =0.07), ethylene glycol (0.25), glycerol (0.44),meso-erythritol (0.71) and adonitol (0.98). This increase in _j (decrease in permeativity) with increasing chain length parallels the decreasing lipid-water partition coefficients of the solutes. The reflection coefficients ofd-sorbitol (1.02) and ofd-mannitol (0.99) indicate that these six-carbon polyhydroxy alcohols are relatively impermeant and hence they would be suitable osmotica in which to suspend mitochondria. The _j 'S varied from 0.96 to 1.02 forD-ribose,D-xylose,D-lyxose,D-arabinose, -D-glucose, -D-glucose,D-galactose,D-mannose, glycine,L-alanine,L-threonine,L-phenylalanine,L-methionine andL-cysteine, indicating that these sugars and amino acids do not readily diffuse across the pair of membranes surrounding potato mitochondria. By contrast, the _j 'S of liver mitochondria for glycine and of pea chloroplasts for most of the same aldopentoses and amino acids are close to zero. Thus, different organelles can vary widely in their permeability properties for nonelectrolytes.