Revisiting Curcumin Chemistry- Part II: Synthesis of Monomethylcurcumin and Isomeric Demethoxycurcumins and their Characterization
College of Pharmaceutical Sciences, Andhra University, Visakhapatnam-530 003, 1Natco research centre, B-13 Industrial estate, Sanathnagar, Hyderabad-500 018, India
College of Pharmaceutical Sciences, Andhra University, Visakhapatnam-530 003, India, E-mail: [email protected]
We have earlier reported the synthesis of the three major curcuminoids of turmeric employing a new strategy involving the use of borontrifluoride instead of boric oxide to protect the active methylene group of acetylacetone in reaction with aromatic aldehydes. We have now synthesized monomethyl products of curcumin and demethoxycurcumin by the same route and characterized them through their physical, chemical and spectral properties. As expected, a single monomethylcurcumin was obtained whereas we got two isomeric, monomethyl demethoxycurcumins when appropriate aromatic aldehydes were used in the condensation reaction. All the compounds were characterized through their difluoroboronites. The isomeric monomethyldemethoxycurcumins, reported for the first time, are distinctly different in melting point, thin layer chromatography and high performance liquid chromatography while their difluorobornites differed in ultra violet spectra. Dimethyl-bis-demethoxycurcumin and its difluoroboronite were prepared for the first time to confirm the involvement of 4/4’-hydroxyl in curcuminoids in quinonoid formation and consequent stability of their difluoroboronites. The monomethylcurcuminoids, especially those of demethoxycurcumin would be of interest for biological activity studies in comparison with curcumin.