Konstantinos E. Litinas

Natural and Synthetic Coumarin Derivatives with Anti-Inflammatory / Antioxidant Activities

Several natural products with a coumarinic moiety have been reported to have multiple biological activities. It is to be expected that, in a similar way to isomeric flavonoids, coumarins might affect the formation and scavenging of reactive oxygen species (ROS) and influence processes involving free radical-mediated injury. Coumarin can reduce tissue edema and inflammation. Moreover coumarin and its 7-hydroxy-derivative inhibit prostaglandin biosynthesis, which involves fatty acid hydroperoxy intermediates. Natural products like esculetin, fraxetin, daphnetin and other related coumarin derivatives are recognised as inhibitors not only of the lipoxygenase and cycloxygenase enzymic systems, but also of the neutrophil-dependent superoxide anion generation. Due to the unquestionable importance of coumarin derivatives considerable efforts have been made by several investigators, to prepare new compounds bearing single substituents, or more complicated systems, including heterocyclic rings mainly at 3-, 4- and/or 7-positions. In this review we shall deal with naturally occurring or synthetically derived coumarin derivatives, which possess anti-inflammatory as well as antioxidant activities.

Synthesis and biological evaluation of several coumarin-4-carboxamidoxime and 3-(coumarin-4-yl)-1,2,4-oxadiazole derivatives

A series of novel coumarin-4-carboxamidoximes 6a-g and 3-(coumarin-4-yl)-1,2,4-oxadiazoles 9a-e were synthesized from coumarin-4-carboxaldehyde 1 via the intermediate coumarin-4-nitriloxide 4. These coumarin derivatives were isolated and characterized, and evaluated for their ability to inhibit trypsin, glucuronidase, and soybean lipoxygenase. The compounds were also tested for antioxidant activity, and as antiiflammatory agents in the rat carrageenin paw edema assay.

Synthesis of hydroxycoumarins and hydroxybenzo[f]- or [h]coumarins as lipid peroxidation inhibitors.

Substituted hydroxycoumarins and 7- or 8-hydroxybenzo[f]coumarins were prepared by the treatment of phenols and naphthalenediols, respectively, with malic acid and H(2)SO(4) under microwave irradiation. 7- or 8-Hydroxybenzo[f]coumarins and 6-hydroxybenzo[h]coumarin were synthesized by the reaction of naphthalenediols with ethylpropiolate in the presence of ZnCl(2) in refluxing dioxane. The compounds were tested in vitro for their ability: (i) to interact with 1,1-diphenyl-2-picryl-hydrazyl (DPPH) stable free radical, (ii) to inhibit lipid peroxidation, (iii) to scavenge the superoxide anion, (iv) to inhibit the activity of soybean lipoxygenase and (v) to inhibit in vivo the carrageenin-induced rat paw edema. Most of them are potent superoxide anion scavengers and inhibit in vitro lipid peroxidation. The majority of the compounds did not show high lipoxygenase inhibitory activity. No differences were observed between biological responses of hydroxycoumarins and hydroxybenzocoumarins. Compound 3i was found to present a promising antioxidant profile.

Synthesis and anti-inflammatory evaluation of novel angularly or linearly fused coumarins

Angular [7,8]-fused coumarins were obtained from the reaction of [2,3]-fused phenols with DMAD and PPh(3), while linear [6,7]-fused coumarins were formed from the analogous reaction of [3,4]-fused phenols with DMAD and PPh(3). These compounds were tested in vitro for antioxidant activity and they found to present significant scavenging activity. In parallel, these new compounds were evaluated in vivo for anti-inflammatory activity and they found to inhibit the carrageenin-induced paw edema (34-65%). Although their interaction with the free stable radical DPPH was low, the methyl 2,2-dimethyl-8-oxo-3,8-dihydro-2H-furo[2,3-h]chromene-6-carboxylate was the most potent (65%) in the in vivo experiment. The later seems to be a potent soybean Lipoxygenase inhibitor and does not acquire gastrointestinal toxicity.

Recent Developments in the Chemistry and in the Biological Applications of Amidoximes

Amidoximes are compounds bearing both a hydroxyimino and an amino group at the same carbon atom which makes them versatile building blocks for the synthesis of various heterocycles. Their importance in chemistry along with their rich biology, make amidoximes an attractive target for medicinal chemists, biochemists and biologists. Amidoximes and simple O-substituted derivatives possess very important biological activities functioning as antituberculotic, antibacterial, bacteriostatic, insecticidal, elminthicidal, antiviral, herbicidal, fungicidal, antineoplastic, antiarrythmic, antihypertensive, antihistaminic, anxiolytic-antidepressant, anti-inflammatory/antioxidant, antiaggregatory (NO donors) or plant growth regulatory agents. A number of amidoximes has already been used as drugs, or currently being in clinical trials. Their numerous pharmaceutical applications have been recently enriched, due to the fact that some mechanistic pathways, concerning their conversion to amidines, as well as their ability to release NO were clarified, giving a new insight to their mode of action and allowing the design of new therapeutic agents. The main subject of the present review paper is to highlight aspects concerning chemical and biological questions on this interesting class of compounds. Some new synthetic methodologies as well as improvements of previously reported general reactions involving amidoximes, acylated amidoximes, and amidines are presented. The biological applications of amidoximes over the end of 2006 are also extensively reviewed.

Novel Cinnamic Acid Derivatives as Antioxidant and Anticancer Agents: Design, Synthesis and Modeling Studies

Cinnamic acids have been identified as interesting compounds with antioxidant, anti-inflammatory and cytotoxic properties. In the present study, simple cinnamic acids were synthesized by Knoevenagel condensation reactions and evaluated for the above biological activities. Compound 4ii proved to be the most potent LOX inhibitor. Phenyl- substituted acids showed better inhibitory activity against soybean LOX, and it must be noted that compounds 4i and 3i with higher lipophilicity values resulted less active than compounds 2i and 1i. The compounds have shown very good activity in different antioxidant assays. The antitumor properties of these derivatives have been assessed by their 1/IC50 inhibitory values in the proliferation of HT-29, A-549, OAW-42, MDA-MB-231, HeLa and MRC-5 normal cell lines. The compounds presented low antitumor activity considering the IC50 values attained for the cell lines, with the exception of compound 4ii. Molecular docking studies were carried out on cinnamic acid derivative 4ii and were found to be in accordance with our experimental biological results.

Convenient synthesis and biological profile of 5-amino-substituted 1,2,4-oxadiazole derivatives

We describe herein a convenient straightforward synthesis of 5-amino-substituted 1,2,4-oxadiazoles, upon the reactions of amidoximes with carbodiimides, as well as their further derivatization to acetamides, in good yields. Most of the compounds exhibited in general low interaction with the stable radical 1,1-diphenyl-2-picryl-hydrazyl. Compounds 32 and 39 inhibited significantly soybean lipoxygenase. Selected compounds were screened for their in vivo anti-inflammatory activity using the carrageenin paw edema model and showed significant anti-inflammatory activity (26, 51%). The ability of the compounds to release NO in the presence of a thiol factor has been also investigated.

1-8H-pyrano[3,2-g]benzoxazol-8-ones from 7-methoxyimino-4-methylchromene-2,8-dione

Abstract 7-Methoxyimino-4-methylchromene-2,8-dione 3, easily prepared from the quinone 1 reacts thermally with methylaromatics 5(a–g), benzyl derivatives 13(a–c), halo derivatives 14(a–c) to give mainly oxazolocoumarins. Products 8(a–d) are obtained from 5(a–d), 13(a–c). Compound 9 is obtained from 5(a–c) and 13(a–c), compounds 15(a–c) are obtained from 14(a–c), the aminophenol 10 and coumarin 16 are obtained from 5f and 14c respectively, while coumarin 12 is obtained from 5g. The reaction of 3 with N-methyl-aniline and N,N-dimethylbenzylamine gives compound 10 and 8a respectively.

The Anti-inflammatory Effect of Coumarin and its Derivatives

Inflammation is the primary host defense mechanism against all forms of injury. Excessive or inadequate activation of the system can have serious effects, as can the failure of inactivation mechanisms. Coumarins can reduce tissue edema and inflammation and inhibit prostaglandin biosynthesis, which involves fatty acid hydroperoxy intermediates. It is to be expected that coumarins might affect the formation and scavenging of reactive substances derived from oxygen species (ROS) and influence processes involving free radical-mediated injury, as can flavonoids. During these years a small number of (Q)SAR studies concerning coumarins as NSAIDs has been presented and reviewed. In this research we tried to examine the structure-function relationship for coumarins, presenting antiinflammatory activity. Coumarin (1), the prototypical compound presents anti-inflammatory activity. The hydroxylaromatic substituted derivatives (5- or 6- or 7-hydroxy or the vicinal dihydroxy) seems to be potent inhibitors of lipoxygenase. Several synthetic derivatives simple or more complicated were found to be potent antiinflammatories/antioxidant agents.

Synthesis of modified homo-N-nucleosides from the reactions of mesityl nitrile oxide with 9-allylpurines and their influence on lipid peroxidation and thrombin inhibition

9-(3-Mesityl-4,5-dihydroisoxazol-5-yl) homo-N-nucleosides were prepared from the 1,3-dipolar cycloaddition reactions of mesityl nitrile oxide with 9-allyl derivatives of 6-chloropurine, 6-piperidinylpurine, 6-morpholinylpurine, 6-pyrrolidinylpurine, and 6-N,N-dibenzoyladenine. The new compounds were tested in vitro for their ability: (i) to interact with 1,1-diphenyl-2-picryl-hydrazyl (DPPH) stable free radical, (ii) to inhibit lipid peroxidation, (iii) to scavenge the superoxide anion, (iv) to inhibit the activity of soybean lipoxygenase, and (v) to inhibit in vitro thrombin. Most of them found to be potent thrombin inhibitors and to inhibit in vitro lipid peroxidation. The majority of the compounds showed significant lipoxygenase inhibitory activity.