Irradiation of ketoprofen in neutral aqueous medium gave rise to 3-ethylbenzophenone as the major photoproduct. Its formation is justified via protonation of a benzylic carbanion or hydrogen abstraction by a benzylic radical. Minor amounts of eight additional compounds were isolated. Four of them are derived from the benzylic radical: 3-(1-hydroperoxyethyl)benzophenone, 3-(1-hydroxyethyl)benzophenone, 3-acetylbenzophenone and 2,3-bis-(3-benzoylphenyl)butane. The other four products involve initial hydrogen abstraction by the excited benzophenone chromophore of ketoprofen: 1,2-bis-(3-ethylphenyl)-1,2-diphenyl-1,2-ethanediol, 2-(3-benzoylphenyl)-1-(3-ethylphenyl)-1-phenylpropan-1-ol, alpha-(3-ethylphenyl)phenylmethanol, 1,2-bis-[3-(2-hydroxycarbonylethyl) phenyl]-1,2-diphenyl-1,2-ethanediol. The latter process was found to mediate the photoperoxidation of linoleic acid through a type I mechanism, as evidenced by the inhibition produced by the radical scavengers butylated hydroxyanisole and reduced glutathione. The major photoproduct, which contains the benzophenone moiety but lacks the propionic acid side chain, also photosensitized linoleic acid peroxidation. Because lipid peroxidation is indicative of cell membrane lysis, the above findings are highly relevant to explain the photobiological properties of ketoprofen.

In the present study we have investigated whether pharmacophore models may account for the activity and selectivity of the known cyclooxygenase-2 (COX-2) selective inhibitors of the phenylsulfonyl tricyclic series, i.e., Celecoxib (1) and Rofecoxib (3), and whether transferring this structural information onto the frame of a nonsteroidal antiinflammatory drug (NSAID), known to tightly bind the enzyme active site, may be useful for designing novel COX-2 selective inhibitors. With this aim we have developed a pharmacophore based on the geometric disposition of chemical features in the most favorable conformation of the COX-2 selective inhibitors SC-558 (2; analogue of Celecoxib (1)) and Rofecoxib (3) and the more restrained compounds 4 (DFU) and 5. The pharmacophore model contains a sulfonyl S atom, an aromatic ring (ring plane A) with a fixed position of the normal to the plane, and an additional aromatic ring (ring plane B), both rings forming a dihedral angle of 290 degrees +/- 10 degrees. The final disposition of the pharmacophoric groups parallels the geometry of the ligand SC-558 (2) in the known crystal structure of the COX-2 complex. Moreover, the nonconserved residue 523 is known to be important for COX-2 selective inhibition; thus, the crystallographic information was used to position an excluded volume in the pharmacophore, accounting for the space limits imposed by this nonconserved residue. The geometry of the final five-feature pharmacophore was found to be consistent with the crystal structure of the nonselective NSAID indomethacin (6) in the COX-2 complex. This result was used to design indomethacin analogues 8 and 9 that exhibited consistent structure-activity relationships leading to the potent and selective COX-2 inhibitor 8a. Compound 8a (LM-1685) was selected as a promising candidate for further pharmacological evaluation.

The stereoselective inhibition of inducible cyclooxygenase (COX-2) by chiral nonsteroidal antiinflammatory drugs (NSAIDs)--ketoprofen, flurbiprofen, and ketorolac--has been investigated. The activity and inhibition of COX-2 was assessed in three different in vitro systems: guinea pig whole blood, lipopolysaccharide (LPS)-stimulated human monocytes, and purified preparations of COX-2 from sheep placenta. The results were compared with the inhibition of constitutive cyclooxygenase (COX-1) in three parallel in vitro models: clotting guinea pig blood, human polymorphonuclear leukocytes, and purified COX-1 from ram seminal vesicles. In the whole blood model, both isoenzymes were inhibited by S-enantiomers with equal potency but S-ketoprofen was the most active on COX-2 (IC50 = 0.024 mumol/L). In contrast, both isoenzymes were inhibited less than 40% by all three R-enantiomers at high concentration (> 1 mumol/L). The inhibition of COX by the R-enantiomers may be attributed to contamination with the S-enantiomers (approximately 0.5%). A significant degree of enantioselectivity in COX-2 inhibition was also observed in intact cells. The S-enantiomers inhibited COX-2 from monocytes with IC50 values in the range of 2 to 25 nmol/L, being 100 to 500-fold more potent than the corresponding R-enantiomers. Finally, S-ketoprofen inhibited COX-2 from sheep placenta (IC50 = 5.3 mumol/L) with slightly less potency than S-ketorolac (IC50 = 0.9 mumol/L) and S-flurbiprofen (IC50 = 0.48 mumol/L), whereas the R-enantiomers were found to be essentially inactive (IC50 > or = 80 mumol/L). It is concluded that the chiral NSAIDs studied here inhibit with comparable stereoselectivity both COX-2 and COX-1 isoenzymes, and that the inhibition of COX-2 previously observed for racemic NSAIDs should be attributed almost exclusively to their S-enantiomers.

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