Design, Synthesis and Evaluation of Novel Carbazole-Derived Photocages

We report the design, synthesis and evaluation of two novel photocages, NCARB and isoNCARB, belonging to the o-nitrobenzyl chemotype and based on the carbazole ring system. The synthesis of each of these isomeric caging molecules was achieved in five steps and in 29 % overall yield, and their photochemical properties were evaluated using benzoic acid as a model for caging. In the event, upon irradiation at 400 nm for 60 min, 82 % and 42 % of benzoic acid was freed from the NCARB and isoNCARB photocages, respectively, whereas only 22 % was released from the nitrodibenzofuran (NDBF) cage. Moreover, the photochemical decaging efficiencies, ϵΦ, of the benzoates photocaged with NCARB and isoNCARB are about 150- and 20-fold better, respectively, at 400 nm than the corresponding caged benzoate derived from NDBF. The water solubility of molecules caged with nitrocarbazole analogs was improved by N-alkylation of NCARB, the better of the two new photocages, with an aminodicarboxylate group. This modified cage, NCARB-DA, was exploited in the design of a caged fluoroquinolone antibiotic, the efficacy of which was illustrated in a bacterial growth inhibition assay, and a phenol-caged tyrosine derivative.