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Communication | Special issue | Vol 99, No. 2, 2019, pp.820-824
Published online, 26th December, 2018
DOI: 10.3987/COM-18-S(F)66
Syntheses and Acid-Stimulus Responsiveness of Aminobenzopyranoxanthene Spiroethers

Ryosuke Hosoda, Shinichiro Kamino,* Masashi Ueda, and Daisuke Sawada*

*Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama-shi, Okayama 700-8530, Japan


Novel aminobenzopyranoxanthene spiroethers (ABPX-SEs) based on the spirocyclization of the hydroxymethyl group were synthesized from ABPX spirolactones (ABPX-SLs). The addition of an acid induces a ring-opening reaction to yield two colored monocationic and dicationic spiro-ring species of ABPX. The acid-stimulus responsiveness of the ABPX-SEs is lower than that of ABPX-SLs in polar organic solvents. In addition, the ABPX-SEs exhibit stepwise structural changes of the three equilibrium species at acidic pH, although rapid conversion from the spirolactone to dicationic species occurs in the case of ABPX-SLs.