Tryptanthrin from indigo: Synthesis, excited state deactivation routes and efficient singlet oxygen sensitization

Tryptanthrin derivatives as efficient singlet oxygen sensitizers

“…Full spectra, including in other solvents (ethanol (EtOH) and methanol (MeOH)), are given in Figure SI14. Similarly to TRYP, the absorption spectra of the different tryptanthrin derivatives, with exception of TRYP-NH 2 , remains relatively unaffected with the polarity and/or hydrogen bonding ability of the solvent [7]. Noteworthy is the different spectral behaviour of TRYP-NH 2 , i.e., absence of the absorption band at shorter wavelengths (~ 350 nm), see Fig.…”

“…The fluorescence quantum yields ( F ) at room temperature (293 K) were measured by the comparative method using the absolute F values obtained for TRYP in each solvent [7] as standard using the equation bellow (Eq. 1):…”

“…The two bromo tryptanthrin derivatives, 3,9-dibromotryptanthrin (TRYP-2Br) and 2,4,8,10-tetrabromotryptanthrin (TRYP-4Br), were successful synthesized from Tyrian purple and Tina blue, respectively. The synthetic methodology previously developed by our research group [7,39] for the synthesis of TRYP from indigo, allows the synthesis of tryptanthrins with two or four bromine atoms from the respective indigo dyes. Using the oxidant system formed by the trio-NaH, 1,2-diodoethane and DMF and microwave irradiation [39], the limitative characteristic of low Scheme 1 Schematic pathways for the synthesis of 3,9-dibromotryptanthrin (TRYP-2Br) from Tyrian purple and 2,4,8,10-tetrabromotryptanthrin (TRYP-4Br) from Tina blue solubility of these indigo dyes in organic solvents was overcome and tryptanthrin analogues were obtained in moderate oxidative conditions and short reaction times, see Scheme 1.…”

“…Tryptanthrin (indolo[2,1-b]quinazoline-6,12-dione), abbreviated as TRYP, is a natural compound found in diversified natural sources [1][2][3][4][5][6] and with several applications. Besides the extraction from natural sources, tryptanthrin can also be synthetically obtained from indigo or isatin increasing the structural diversity of tryptanthrin derivatives [7][8][9][10][11]. To increase the bioactivity of TRYP, several structural modifications have been accomplished.…”

“…Recently the role of N,N'-dimethylformamide (DMF) to act as solvent and oxygen source in the formation of TRYP from indigo was investigated [39], this showed a new approach for the synthesis of TRYP from indigo via oxidation to isatin and subsequent oxidative cyclization by using the trio -sodium hydride (NaH), an iodine source and DMF under microwave irradiation [7,39]. The developed methodology allows the synthesis of new tryptanthrin derivatives from well-known and available indigo dyes.…”