The method described herein is a very powerful tool for rapid synthesis, separation, and screening of combinatorial libraries on planar media. Thirty compounds were synthesized and separated affording discrete chemical entities, including by-products, which were screened for antioxidant activity. The whole process from synthesis to screening was performed manually and took between 30 and 60 min after optimization of the reaction.A series of coumarin derivatives was synthesized by
condensation of salicylaldehyde derivatives with active methylene species, assisted by microwave irradiation, using a TLC plate as planar support. Elution of the reaction mixtures afforded discrete coumarin products which were screened directly on the plate for antioxidant activity against the 1,1-diphenyl-2-picrylhydrazyl (DPPH) test radical.Active compounds were scaled-up and re-screened for potency in comparison with Irgafos 38, a known antioxidant commonly incorporated as an additive in plastics. The potency of all the active species was of the same order of magnitude as that of Irgafos 38. The lower limit of activity of 8-hydroxy-2-oxo-2
-chromene-3-carboxylic acid ethyl ester was 600 ng compared with 700 ng for Irgafos 38.
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