A valid model for the mechanism of oxidation of tryptophan to formylkynurenine-25 years later

The dye-sensitized photooxygenation of DL-tryptophan in aqueous solution leads to the tricyclic compound 2-carboxy-3a-hydroperoxy-1,2,3,3a,8,8a-hexahydropyrrolo[2,3-b]indole which, on reduction with dimethyl sulfide, furnishes two diastereoisomeric alcohols separable by fractional crystallization into a higher melting (mp 254 degrees -256 degrees ) and a lower melting (mp 228 degrees ) diastereoisomer. Each of these alcohols was correlated with one of the analogous pair of isomeric 1,2-dicarbomethoxy analogs by alkaline hydrolysis and by x-ray analysis. In this way, the 3a-hydroxy-1,2-dimethoxycarbonyl- 1,2,3,3a,8,8a-hexahydropyrrolo[2,3-b]indole, mp 163 degrees -164 degrees , was shown to have the trans configuration with regard to the relative positions of the hydroxyl and carbomethoxy groups and that, on alkaline hydrolysis, it produced the isomer with mp 228 degrees , which therefore also has the trans configuration. The mechanism of the smooth thermal rearrangement of the (presumably ring-chain tautomeric) tryptophan hydroperoxy intermediates to formylkynurenine is discussed with its implications for the biological oxidation by tryptophan 2,3-dioxygenase.

Crystal and molecular structure of a thymine phototrimer

Thymine trimer was isolated from a frozen aqueous solution of thymine which was irradiated with ultraviolet light and was presumably formed through the rearrangement of an initial oxetane photoproduct. X-ray diffraction analysis of a single crystal has confirmed the trimeric diol structure and has established the stereoconfiguration of the molecule. The possible importance of the diol structure in photobiology is pointed out.