Sulphydryl compounds in melanogenesis.Part II.Reactionof cysteine and glutathione with dopachrome.

Under biomimetic conditions dopachrome (I, R = R1 = H), a key intermediate in the biosynthesis of melanins, is shown to react with glutathione to give a colorless adduct identified as 4-S-glutathionyl-5,6-dihydroxyindole (II, R2 = S-glutathionyl). In the case of cysteine, the reaction leads to a non-aminoacidic condensation product (λmax 422 nm) which was too unstable to be characterized. The analogous adduct derived by reaction of dopachrome Me ester (I, R = H, R1 = Me) with cysteine Et ester (IV) could be isolated and formulated as II (R = R3 = H, R4 = Et), contg. the new 1,2-dihydro-3H,8H-pyrrolo[2,3-h][1,4]benzothiazine ring system. Likewise, 2-methyldopachrome Me ester (I, R = R1 = Me) reacts with IV and penicillamine Me ester to give the corresponding adducts III (R = Me, R3 = H, R4 = Et; R = R3 = R4 = Me, resp.).