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PREPARATION AND PROPERTIES OF PHOTOPRODUCTS OF OROTIC ACID ANALOGUES *
Author(s) -
Sztumpf Eva,
Shugar D.
Publication year - 1965
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1965.tb07914.x
Subject(s) - orotic acid , dimer , chemistry , dissociation (chemistry) , photochemistry , photodissociation , uracil , oxygen , thymine , acetic acid , organic chemistry , dna , biochemistry
Abstract— Irradiation of orotic acid or 3‐methylorotic acid in liquid medium in the quartz U.V. leads to formation of photoproducts which have been shown to be dimers similar to those formed from uracil or thymine in frozen solution. The dimers are subject to photo‐dissociation in the same wavelength range, so that at any given wavelength there is a stationary equilibrium between dimer formation and dissociation. The equilibrium point is also dependent on concentration, and on pH, the dimerization reaction being more rapid for the neutral forms. For both compounds there is an appreciable oxygen effect, which inhibits dimer formation. I‐methylorotic acid and 1,3‐dimethylorotic acid also dimerize, but the oxygen effect is diminished as a result of alkylation on the N 1 ring nitrogen. 5‐methylorotic acid is radiation resistant in liquid medium, but readily dimerizes in frozen medium; the subsequent photodissociation of this dimer in liquid medium is unaffected by oxygen. Orotidine forms several photoproducts of which one, about 20 per cent of the total, is a similar dimer. Orotic acid methyl ester likewise dimerizes in liquid medium and exhibits an oxygen effect comparable to that for orotic acid. By contrast 5‐methylorotic acid methyl ester in liquid medium is radiation resistant at short wavelengths, but dimerizes at long wavelengths. The dimers of orotic acid, 3‐methylorotic acid, 5‐methylorotic acid and orotidine have been isolated in crystalline form. The properties of the various photodimers are described and quantum yields for dimerization and photodissociation calculated for several of them at 254 mμ. For orotic and 3‐methylorotic acids the high quantum yields for dimerization and the appreciable oxygen effect suggest that the dimerization of these molecules proceeds via a long‐lived excited state.