title: One-pot synthesis of highly fluorescent pyrido[1,2-a]indole derivatives through C-H/N-H activation: photophysical investigations and application in cell imaging.
abstract: We describe a straightforward strategy for the synthesis of strongly fluorescent pyridoindoles by Pd-catalyzed oxidative annulations of internal alkynes with C-3 functionalized indoles through CH/NH bond activation in a one-pot tandem process. Mechanistic investigations reveal the preferential activation of NH indole followed by CH activation during the cyclization process. Photophysical properties of pyridoindoles exhibited the highest fluorescence quantum yield of nearly 80 %, with emission color varying from blue to green to orange depending on the substructures. Quantum mechanical calculations provide insights into the observed photophysical properties. The strong fluorescence of the pyrido[1,2-a]indole derivative has been employed in subcellular imaging, which demonstrates its localization in the cell nucleus.
authors.affiliation: Medicinal and Process Chemistry Division, CSIR-Central Drug Research Institute, Lucknow, 226031 (India), Fax: (+91) 522-2623405.
authors.forename: Srinivas
authors.initials: S
authors.lastname: Samala
authors.forename: Pragyan
authors.initials: P
authors.lastname: Pallavi
authors.forename: Ravi
authors.initials: R
authors.lastname: Kumar
authors.forename: Rajesh K
authors.initials: RK
authors.lastname: Arigela
authors.forename: Gajendra
authors.initials: G
authors.lastname: Singh
authors.forename: Ravi Sankar
authors.initials: RS
authors.lastname: Ampapathi
authors.forename: Amulya
authors.initials: A
authors.lastname: Priya
authors.forename: Sunando
authors.initials: S
authors.lastname: Datta
authors.forename: Abhijit
authors.initials: A
authors.lastname: Patra
authors.forename: Bijoy
authors.initials: B
authors.lastname: Kundu
mesh_terms: D002384:Catalysis; D003500:Cyclization; D005456:Fluorescent Dyes / Q000138:chemical synthesis / Q000737:chemistry; D007211:Indoles / Q000138:chemical synthesis* / Q000737:chemistry*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D055668:Photochemical Processes; D011725:Pyridines / Q000138:chemical synthesis* / Q000737:chemistry*
chemical_list: D005456:Fluorescent Dyes; D007211:Indoles; D011725:Pyridines
keywords: alkynes; fluorescence; imaging agents; nitrogen heterocycles; quantum yield