7‑Guanidinyl Coumarins: Synthesis, Photophysical Properties, and Application to Exploit the Pd-Catalyzed Release of Guanidines

Molecularmanipulation of guanidino-containing biomoleculesina cellular environment is fundamental to exploiting protein functionand drug release, but currently, there is a lack of suitable methodsfor reaction screening and monitoring. To exploit the potential ofthe fluorescent method in this respect, herein, we evaluated a novelarray of 7-guanidinyl coumarins by incorporating different substitutedguanidino moieties into a coumarin scaffold. These compounds wereprepared by guanidinylation reagent S-methylisothioureaor TFA-protected pyrazole-carboxamidine. Examination of their photophysicalproperties revealed that the fluorescence emission of alkyloxycarbonyl-substitutedguanidinyl coumarin was significantly enhanced as compared with theunsubstituted analogue. This dramatic fluorescence difference enabledpreliminary exploitation of the Pd-catalyzed release of allyloxycarbonyl(Alloc)-caged guanidinyl coumarin-6 in living cells.