Linker-Free Near-IR Aza-BODIPY-Glutamine Conjugates Through Boron Functionalization
Abstract
© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim A series of linker-free aza-BODIPY-glutamine conjugates were synthesized and investigated, both experimentally and computationally. The structures of the aza-BODIPYs were confirmed spectroscopically, and in the case of 3a an X-ray structure was obtained. All aza-BODIPYs show intense absorption bands between 642–667 nm and fluorescence emissions between 691–703 nm. The fluorescence quantum yields of the 2,6-unsubstituted compounds 1a–4a were found to be Φf ≈ 0.2 in chloroform, while those of the corresponding 2,6-dibrominated derivatives 1b–4b were less than 0.01. The cytotoxicity and cellular uptake of all aza-BODIPYs were investigated in human carcinoma HEp2 cells. The most cytotoxic aza-BODIPYs were found to be 3a and 3b, due to the presence of the cyclic N,O-bidentate amino acid ring, rather than the presence of the 2,6-bromine atoms. The results show that the mode of glutamine conjugation to the aza-BODIPY determines the stability and cytotoxicity of the conjugates.