Expedient Synthesis of Indolo[2,3- b ]quinolines, Chromeno[2,3- b ]indoles, and 3-Alkenyl-oxindoles from 3,3'-Diindolylmethanes and Evaluation of Their Antibiotic Activity against Methicillin-Resistant Staphylococcus aureus .

Easily accessible 3,3'-diindolylmethanes (DIMs) were utilized to generate a focused library of indolo[2,3- b ]quinolines ( 2 ), chromeno[2,3- b ]indoles ( 3 ), and 3-alkenyl-oxindoles ( 4 ) under 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)-mediated oxidative conditions. DIMs with ortho-NHTosyl (NHTs) phenyl group afforded indolo[2,3- b ]quinolines ( 2 ), whereas DIMs with ortho-hydroxy phenyl groups yielded chromeno[2,3- b ]indoles ( 3 ) and 3-alkenyl-oxindoles ( 4 ). The mild conditions and excellent yields of the products make this method a good choice to access a diverse library of bioactive molecules from a common starting material. Two optimized compounds 2a and 2n displayed excellent activity against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA). Compound 2a showed the minimum inhibitory concentration values in the concentration between 1 and 4 μg/mL, whereas compound 2n revealed the values of 1-2 μg/mL. Furthermore, both the compounds were highly bactericidal and capable to kill the MRSA completely within 360 min. Collectively, the results suggested that both compounds 2a and 2n possess enormous potential to be developed as anti-MRSA agents.
Competing Interests: The authors declare no competing financial interest.