Synthesis of α‐ and β‐Pyran Naphthoquinones as a New Class of Antitubercular Agents

A series of alpha- and beta-pyran naphthoquinones (lapachones) have been synthesized and evaluated for their in-vitro antibacterial activity against Mycobacterium tuberculosis strain H37Rv (ATCC 27294) using the Alamar-Blue susceptibility test; the activity was expressed as the minimum inhibitory concentration (MIC) in microg/mL. The synthetic methodology consisted of the formation of methylene and aryl o-quinone methides (o-QMs) generated by Knoevenagel condensation of 2-hydroxy-1,4-naphthoquinone with formaldehyde and arylaldehydes. These o-QMs then undergo facile hetero Diels-Alder reactions with dienophiles in aqueous ethanol media. Some naphthoquinones exhibited inhibition with MIC values of 1.25 microg/mL, similar to that of pharmaceutical concentrations currently used in tuberculosis treatment. These results justify further research into the value of these quinones as part of an original treatment for tuberculosis.