A REVIEW ON BIOLOGICAL ACTIVITY AND SYNTHETIS OF COUMARINS

Coumarin (1,2-Benzopyrone or 2H-1-benzopyran-2-one, or phenylpropanoids, 1) and its derivatives (coumarins) are widely distributed throughout nature and many exhibit useful and diverse biological activities1,2. Coumarins occur as secondary metabolites in the seeds, roots and leaves of many plant species, notably in high concentration in the tonka bean and thus the name comes from a French word, coumarou, for the tonka bean. Their function is far from clear, although suggestions include plant growth regulations, fungistasis, bacteriostasis and, even, waste products3 . Some naturally occurring coumarin derivatives include warfarin (2), umbelliferone (7- hydroxycoumarin, 3), aesculetin (6,7-dihydroxycoumarin, 4), herniarin (7-methoxycoumarin, 5), psoralen (6) and imperatorin (7). Now the diversity of coumarin derivatives, both natural and synthetic, has grown and are thus divided into several subclasses. Most reviews classify coumarins according to whether particular compounds are simple coumarins (e.g. coumarin, 1 and limettin, 8), linear furanocoumarins (e.g. imperatorin, 7 and isopimpinellin, 9), angular furanocoumarins (e.g. angelicin, 10), linear pyranocoumarins (e.g. xanthyletin, 11) or angular pyranocoumarins (e.g. seselin, 12) 4 . Murray et al. 5 however, used a biogenetic approach based upon the number of nuclear oxygen atoms in classifying coumarin-containing compounds. Because of their varied biological activities, the preparation of coumarin and its derivatives has attracted the attention of organic chemists. Various synthetic methods have been developed for the synthesis of coumarin. These include use of the Knoevenagel condensation,Wittig reactions, Perkin reaction and Pechmann reaction.