Isabel M. Morera

PHOTOLYTIC DEGRADATION OF IBUPROFEN. TOXICITY OF THE ISOLATED PHOTOPRODUCTS ON FIBROBLASTS and ERYTHROCYTES

The photodegradation of Ibuprofen, a widely used non‐steroidal anti‐inflammatory drug (NSAID), was examined. Several photoproducts (I‐VI) were isolated and identified on the basis of their IR‐1H‐NMR‐ and 13C‐NMR‐ spectra. The chemical structures were confirmed by unambiguous alternative synthesis from available reagents. The most significant primary photochemical process was the cleavage of the C‐C bond a to the carboxy group. Subsequent secondary processes (hydrogen abstraction, dimerization, incorporation of methanol, or reaction with oxygen) might account for the formation of the different photoproducts. The cytotoxic effects were assayed using the red‐blood cell lysis test and the enzyme leakage (LDH and GOT) from cultured fibroblasts. Compound V [l‐(4 isobutylphenyl)‐ethanol] was found to be toxic for both system at concentrations greater than 1 mM while compound IV [l‐(4 isobutylphenyl acetophenone)] was toxic for fibroblasts but not for erythrocytes at the same concentration. Ibuprofen and the other photocompounds were apparently non‐toxic. The significance of these results is discussed in connection with the possible in vivo phototoxicity of Ibuprofen.

In vitro assessment of the phototoxicity of anti-inflammatory 2-arylpropionic acids.

We have combined photochemical and physicochemical studies with in vitro testing on human fibroblasts and erythrocytes to investigate the photobiological risk of four non-steroidal anti-inflammatory drugs (NSAID)-ibuprofen, butibufen, flurbiprofen and naproxen. Under aerobic conditions these compounds undergo photodecarboxylation, mainly to benzylic alcohols and aromatic ketones. The photoproducts have been purified and chemically identified. While parent compounds showed very little or no phototoxicity, the most toxic photoproducts were systematically the benzylic alcohols, which showed lytic activity to erythrocytes and cytotoxicity to cultured fibroblasts. The results partly explain the in vivo phototoxicity of this family of drugs.

Phototoxicity of non-steroidal anti-inflammatory drugs: in vitro testing of the photoproducts of Butibufen and Flurbiprofen

In this work, the phototoxicity of two non-steroidal anti-inflammatory drugs, Butibufen and Flurbiprofen, was examined. Both were unstable to light, to give several photoproducts which were isolated and identified. The different photoproducts were formed by a primary photochemical mechanism which involves an initial cleavage of the C-C bond alpha to the carbonyl group, followed by several secondary processes. The cytotoxic effects of the xenobiotics were evaluated using two well-established biological in vitro tests: (a) enzyme leakage lactate dehydrogenase and glutamate-oxaloacetate transaminase from cultured fibroblasts and (b) lysis of red blood cells. The benzylic alcohols caused extensive leakage from cultured fibroblasts at the different concentrations assayed. The alcohol obtained from Butibufen was a potent lytic agent for human red blood cells. The other photoproducts, Butibufen and Flurbiprofen did not produce observable toxic effects on cells.

Chiral discrimination in the intramolecular abstraction of allylic hydrogens by benzophenone triplets

Using two diastereomeric compounds containing benzophenone and olefin units, significant chiral discrimination has been found in all the photophysical and photochemical processes involved in intramolecular hydrogen abstraction: overall quenching of benzophenone triplets, actual hydrogen abstraction step and π-quenching.

Mechanism of Lipid Peroxidation Photosensitized by Tiaprofenic Acid: Product Studies Using Linoleic Acid and 1,4-Cyclohexadienes as Model Substrates¶

Abstract A careful study of the linoleic acid hydroperoxide (LOOH) profile obtained upon peroxidation of linoleic acid (LA) photosensitized by tiaprofenic acid (TPA) and analogous ketones has been undertaken to distinguish between type-I and type-II photoperoxidation mechanisms. 1,4-Cyclohexadiene and 1,2-dimethylcyclohexa-2,5-dienecarboxylic acid (CHDCA) have also been used as models for LA since they also have double allylic systems. Coirradiation of LA with TPA and decarboxytiaprofenic acid (DTPA) in acetonitrile and micellar media produced significant amounts of conjugated dienic LOOH. The cis,trans to trans,trans ratio depended on the irradiation time; thus, this parameter is an ambiguous tool for mechanistic assignment. An interesting finding was the decrease of the LOOH level after long irradiation times in mixtures photooxidized by DTPA, which is attributed to quenching of the DTPA triplet by the generated dienic LOOH. High-performance liquid chromatography analyses confirmed that the main pathway operating in photodynamic lipid peroxidation sensitized by (D)TPA is a type-I mechanism. However, product studies using CHDCA have clearly shown that a type-II mechanism is also operating and might contribute to the overall photooxidation process in a significant way.

Photobinding of Tiaprofenic Acid and Suprofen to Proteins and Cells: A Combined Study Using Radiolabeling, Antibodies and Laser Flash Photolysis of Model Bichromophores

Drug photoallergy is a matter of current concern. It involves the formation of drug‐protein photoadducts (pho‐toantigens) that may ultimately trigger an immunological response. Tyrosine residues appear to be key binding sites in proteins. The present work has investigated the photobinding of tiaprofenic and (TPA) and the closely related isomer suprofen (SUP) to proteins and cells by means of radioactive labeling and drug‐directed antibodies. To ascertain whether preassociation with the protein may play a role in photoreactivity, two model bichro‐mophoric compounds (TPA‐Tyr and SUP‐Tyr) have been prepared and studied by laser flash photolysis. The results of this work show that (a) TPA and SUP photo‐bind to proteins with similar efficiencies, (b) both drugs form photoadducts that share a basic common structure, as they are recognized by the same antibody and (c) drug‐protein preassociation must play a key role in photoreactivity, as indicated by the dramatic decrease in the triplet state lifetimes of the model bichromophores compared to the parent drugs.

Photochemistry of 2(3H)- and 2(5H)-furanones

Par reaction photochimique des dihydro-2,3- et -2,5 furannones-2, on obtient une decabonylation, une decarboxylation, une cyclisation, une dimerisation ou des transpositions de substituants

Solvent effects in hydrogen abstraction from cholesterol by benzophenone triplet excited state.

Hydrogen abstraction from the C-7 position of cholesterol (Ch) by triplet excited benzophenone (BZP) exhibits remarkable solvent-dependence in product studies. Kinetic measurements on the intramolecular version of the process in dyads containing covalently linked Ch and BZP units reveal important solvent effects and significant stereodifferentiation.

Probing Lipid Peroxidation by Using Linoleic Acid and Benzophenone

A thorough mechanistic study has been performed on the reaction between benzophenone (BZP) and a series of 1,4-dienes, including 1,4-cyclohexadiene (CHD), 1,4-dihydro-2-methylbenzoic acid (MBA), 1,4-dihydro-1,2-dimethylbenzoic acid (DMBA) and linoleic acid (LA). A combination of steady-state photolysis, laser flash photolysis (LFP), and photochemically induced dynamic nuclear polarization (photo-CIDNP) have been used. Irradiation of BZP and CHD led to a cross-coupled sensitizer-diene product, together with 6, 7, and 8. With MBA and DMBA as hydrogen donors, photoproducts arising from cross-coupling of sensitizer and diene radicals were found; compound 7 was also obtained, but 6 and o-toluic acid were only isolated in the irradiation of BZP with MBA. Triplet lifetimes were determined in the absence and in the presence of several diene concentrations. All three model compounds showed similar reactivity (k(q) ≈10(8)  M(-1)  s(-1)) towards triplet excited BZP. Partly reversible hydrogen abstraction of the allylic hydrogen atoms of CHD, MBA, and DMBA was also detected by photo-CIDNP on different timescales. Polarizations of the diamagnetic products were in full agreement with the results derived from LFP. Finally, LA also underwent partly reversible hydrogen abstraction during photoreaction with BZP. Subsequent hydrogen transfer between primary radicals led to conjugated derivatives of LA. The unpaired electron spin population in linoleyl radical (LA(.)) was predominantly found on H(1-5) protons. To date, LA-related radicals were only reported upon hydrogen transfer from highly substituted model compounds by steady-state EPR spectroscopy. Herein, we have experimentally established the formation of LA(.) and shown that it converts into two dominating conjugated isomers on the millisecond timescale. Such processes are at the basis of alterations of membrane structures caused by oxidative stress.

Stereoselective intramolecular hydrogen abstraction by a chiral benzophenone derivative.

An unprecedented stereoselective photoreduction of a chiral BZP is observed in steady state as well as in time-resolved studies.