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.

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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. Phenylsubstituted 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/IC 50 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 IC 50 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.

Reaction of compound 3 with nitrile oxide 4a affords compounds 5a and 6 in 73% and 3% yield respectively, while reaction of 3 with 4b affords only compound 5b (85%). Reactions of compound 8 with the nitrile oxides 4a,b result in compounds 9a,b. The compound 10, prepared from 1 and O‐methylhydroxylamine, reacts with nitrile oxide 4b to give the oxadiazole derivative 12. The above referred coumarins are screened for antiinflammatory activity in vivo using the carrageenin rat paw edema and in vitro through their antiproteolytic activity and their ability to inhibit β‐glucuronidase and 12‐Lipoxygenase.

A series of novel 3-(coumarin-4-yl)tetrahydroisoxazoles 5a,b, 7, 9 and 3-(coumarin-4-yl)dihydropyrazoles 13a-d, 14, 15a,b were synthesized from coumarin-4-carboxaldehyde 1 via the intermediate N-methyl nitrone 3 and N-phenyl or N-methyl hydrazones 11a,b. These coumarin derivatives were isolated, characterized and evaluated in vitro for their ability to inhibit trypsin, β-glucuronidase, soybean lipoxygenase and to interact with the stable radical 1,1-diphenyl-2-picrylhydrazyl. The compounds were tested in vivo as antiinflammatory agents in the rat carrageenin paw edema assay. Compound 15a seems to be a lead molecule to be modified in order to improve the lipoxygenase inhibition. The results are discussed in terms of structural characteristics.J. Heterocyclic Chem., 38, 717 (2001).Coumarins have been reported to have multiple biological activities [1]. It is to be expected that coumarins might affect the formation and scavenging of reactive substances derived from oxygen (Reactive Oxygen Species, ROS) and influence processes involving free radical-mediated injury, as can some other plant phenolics and flavonoids [2,3]. There is evidence that the naturally occuring prototypical compound, coumarin can reduce tissue oedema and inflammation [4]. Coumarin and 7-hydroxycoumarin inhibit prostaglandin biosynthesis, which involves fatty acid hydroperoxy intermediates [5]. Various coumarin related derivatives are recognised as inhibitors not only of the lipoxygenase and cyclooxygenase pathways of arachidonate metabolism [6,7,8], but also of neutrophile dependent superoxide anion generation [9].In connection to our previous work on the synthesis of coumarin derivatives [10][11][12][13][14] In continuation to these studies we tried to design and synthesize novel coumarins like the new 4-(3'-tetrahydroisoxazolyl)-and 4-(3'-dihydropyrazolyl)coumarin derivatives and to define structure features for active compounds and to discuss our results in terms of structure-activity relationships. The reactions studied and the products (new compounds) obtained are depicted in schemes 1-2.We prepared previously 4-(3'-isoxazolinyl)coumarins through 1,3-cycloaddition reactions of 2-oxo-2H-[1]benzopyran-4-carbonitrile N-oxide with different dipolarophiles [16]. In this work we try to extend those 1,3-cycloaddition reactions by preparing the new dipoles 3 and 12a,b and studying their reactions with dipolarophiles 4a,b, 6, 8.Treatment of ethanol solution of aldehyde 1 with Nmethyl hydroxylamine hydrochloride 2 and sodium acetate under reflux (Scheme 1) gave as a precipitate, after ice/water work up, the new nitrone 3 (54% yield). Reactions of compound 3 with maleimides 4a,b resulted to new isoxazolidines 5a (47%), 5b (83%) respectively as the sole 1,3-cycloadducts. The chemical shifts for 5-H (5.02, d, J = 7.6 Hz), 3-H (4.82, d, J = 2.5 Hz), 4-H (3.94, dd, J 1 = 2.5 Hz, J 2 = 7.6 Hz) of 5a and 5-H (4.92, d, J = 7.4 Hz), 3-H (4.66, d, J = 2.7 Hz), 4-H (3.79, dd, J 1 = 2.7 Hz, J = 7.4 Hz) of 5b resemble well with the proposed structures in analogy...