Abstract
| - The UV irradiation of pyrrolnitrin (1a), which is an antibiotic clinically useful against dermatophytosis and possesses a unique 2-(pyrrol-3-yl)nitrobenzene moiety in the molecule, in an anhydrousaprotic solvent resulted in the exclusive formation of transient 7,4‘-dichlorospiro[1,3-dihydrobenzo(c)isoxazole-3,3‘-pyrrolin-2‘-one] (2a) via the intramolecular oxidation of the juxtaposed pyrrole ringby the triplet-excited nitro group. The irradiation in an aqueous aprotic solvent, however, allowedthe concurrent occurrence of intramolecular cyclization by the singlet-excited nitro group in 1aand the hydroxylation at the 2-position of the pyrrole ring by water to afford 3,7-dichloro-8-hydroxy-8,8a-dihydropyrrolo[2,3-b]indol-2-one (3a), accompanied by the formation of 2a. Elongation of theirradiation time in these photoreactions caused a rapid consumption of the products, 2a and 3a, togive undetermined polar polymeric products. The present results indicate that the photodegradationof 1a is significantly influenced by the presence of water in the reaction media and by the natureof its excited state. Thus, the loss of the antifungal activities by the photosensitive antibiotic 1awas chemically proved.
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