Design and synthesis of new 1,3-benzthiazinan-4-one derivatives as selective cyclooxygenase (COX-2) inhibitors
Graphical abstract
A new group of 1,3-benthiazinan-4-ones, possessing a methyl sulfonyl pharmacophore, were synthesized and their biological activities were evaluated for cyclooxygenase-2 (COX-2) inhibitory activity. In vitro COX-1/COX-2 structure–activity relationships were determined by varying the substituents on the N-3 of 1,3-benzthizinane ring.
Introduction
The non-steroidal anti-inflammatory drugs (NSAIDs) are among the most commonly medications in the world. The mechanism of action of these drugs is the inhibition of cyclooxygenase (COX) enzyme, which catalyzes the first step of the biosynthesis of PGG2 from arachidonic acid.1 A major factor limiting their use is gastrointestinal toxicity, ranging from ulcer to perforation and bleeding.2 COX isozymes exist at least in two isoforms, COX-1 and COX-2.3 The COX isoforms are heme containing enzymes that exhibit distinct expression roles in several physiological processes. The constitutive COX-1 isozyme is found in platelets, kidneys, and the gastrointestinal tract and is believed to be responsible for the maintenance of physiological functions such as gastro protection and vascular homeostasis.4 In contrast, the COX-2 enzyme is the inducible isoform that is produced by various cell types upon exposure to cytokines, mitogens, and endotoxins released during injury and therefore molecules that inhibit it s enzymatic activity would be of therapeutic value.5, 6 The gastrointestinal side effects associated with NSAIDs are due to the inhibition of gastroprotective PGs synthesized through the COX-1 pathway.7 Thus, selective inhibition of COX-2 over COX-1 is useful for the treatment of inflammation and inflammation-associated disorders with reduced gastrointestinal toxicities when compared with NSAIDs. Moreover, recent studies indicating the place of COX-2 inhibitors in cancer chemotherapy8 and neurological diseases such as Parkinson9 and Alzheimer’s10 diseases still continue to attract investigations on development of COX-2 inhibitors. The majority of selective COX-2 inhibitors belong to a class of diarylheterocycles that possess vicinal diaryl substitution attached to a mono or bicyclic central ring system.11, 12, 13, 14, 15, 16, 17, 18 In this regard, many classes of selective COX-2 inhibitors such as coxibs have been developed with desired selectivity. The coxibs (e.g., celecoxib and rofecoxib, Fig. 1)11, 12 for treating pain and inflammation associated with arthritis have been shown to be well tolerated and reduce GI side effects. The recent market withdrawal of some coxibs such as rofecoxib and valdecoxib due to their adverse cardiovascular side effects19 clearly delineates the need to develop alternative structures with COX-2 inhibitory activity. In addition, some studies have suggested that rofecoxib adverse cardiac events may not be a class effect but rather an intrinsic chemical property related to its metabolism.20 For this reason novel scaffolds with high selectivity for COX-2 inhibition need to be found and evaluated for their anti-inflammatory effects. Recently, we reported several investigations describing the design, synthesis and molecular modeling studies for 1,3-thiazolidine-4-ones17 and 1,3-thiazinan-4-ones18 possessing a five or six membered central ring and methylsulfonyl COX-2 pharmacophore at the para-position of C-2 phenyl ring in conjunction with different substituents at the N-3 of the central ring. For example, 3-(4-fluorophenyl)-2-(4-methylsulfonylphenyl)-1,3-thiazolidine-4-one and 3-benzyl-2-(4-methyl sulfonylphenyl)-1,3-thiazinan-4-one (see structures 1 and 2) exhibited highly selectivity for COX-2 inhibition. As a part of our ongoing program to design new types of selective COX-2 inhibitors, we now report the design, synthesis, cyclooxygenase inhibitory and some molecular modeling studies of a group of 1,3-benzthiazinan-4-one derivatives having a new bicyclic central ring scaffold and different substituents at the N-3 in order to find the effect of these substituents on the inhibition of COX-2 activity.
Section snippets
Chemistry
The target 1,3-benzthiazinan-4-one derivatives (7a–f) were synthesized via the route outlined in Scheme 1. Accordingly, 4-methylsulfonylbenzaldehyde (4) was treated with an appropriate amine (5a–f) and thiosalicylic acid (6) in dry toluene in the presence of p-toluenesulfonic acid under reflux to give 2-(4-methylsulfonylphenyl)-3-substituted-1,3-benzthiazinan-4-one (7a–f, 33–73%).18 The purity of all products was determined by thin layer chromatography using several solvent systems of different
Results and discussion
A group of 1,3-benzthiazinan-4-one derivatives having different substituents at the N-3 of central ring (7a–f) were prepared to investigate the effect of different substituents on COX-2 selectivity and potency. The ability of the 1,3-benzthiazinan-4-ones 7a–f to inhibit the COX-1 and COX-2 isozymes was determined using chemiluminescent enzyme assays (see enzyme inhibition data in Table 1.) according to our previously reported method.17 In vitro COX-1/COX-2 inhibition studies showed that all
Conclusions
The results of this investigation indicate that (i) the 1,3-benzthiazinan-4-one moiety is a suitable scaffold (template) to design COX-2 inhibitors, (ii) in this class of compounds COX-1/-2 inhibition is sensitive to the nature of the N-3 substituents, and (iii) 3-(p-fluoropheny)-2-(4-methylsulfonylphenyl)-1,3-benzthiazinan-4-one (7b) exhibited high COX-2 inhibitory potency and selectivity.
Experimental
All chemicals and solvents used in this study were purchased from Merck AG and Aldrich Chemical. Melting points were determined with a Thomas–Hoover capillary apparatus. Infrared spectra were acquired using a Perkin Elmer Model 1420 spectrometer. A Bruker FT-500 MHz instrument (Brucker Biosciences, USA) was used to acquire 1H NMR spectra with TMS as internal standard. Chloroform-D and DMSO-d6 were used as solvents. Coupling constant (J) values were estimated in hertz (Hz) and spin multiples were
Molecular modeling (docking) studies
Docking studies were performed using Autodock software Version 3.0.5. The coordinates of the X-ray crystal structure of the selective COX-2 inhibitor SC-558 bound to the murine COX-2 enzyme was obtained from the RCSB Protein Data Bank (1c×2) and hydrogens were added. The ligand molecules were constructed using the Builder module and were energy minimized for 1000 iterations reaching a convergence of 0.01 kcal/mol Å. The energy minimized ligands were superimposed on SC-558 in the PDB file 1cx2
In vitro cyclooxygenase (COX) inhibition assays
The assay was performed using an enzyme chemiluminescent kit (catalog number 760101, Cayman chemical, MI, USA) according to our previously reported method.17 The Cayman chemical chemiluminescent COX (ovine) inhibitor screening assay utilizes the heme-catalyzed hydroperoxidase activity of ovine cyclooxygenases to generate luminescence in the presence of a cyclic naphthalene hydrazide and the substrate arachidonic acid. Arachidonate-induced luminescence was shown to be an index of real-time
Acknowledgements
We are grateful to Research deputy of Shahid Beheshti University (M.C) for financial support of this research.
References and notes (21)
Biochem. Biophys. Acta
(1996)- et al.
Adv. Clin. Chem.
(2007) - et al.
Gasteroenterology
(1995) - et al.
Bioorg. Med. Chem. Lett.
(1999) - et al.
Bioorg. Med. Chem.
(2007) - et al.
Bioorg. Med. Chem. Lett.
(2007) - et al.
Bioorg. Med. Chem. Lett.
(2009) - et al.
J. Lipid Mediators Cell Signalling
(1995) - et al.
Ann. Rev. Pharmacol. Toxicol.
(1998) - et al.
Proc. Natl. Acad. Sci. U.S.A.
(1991)