Characterisation of 1,4-benzothiazine intermediates in the oxidative conversion of 5-S-cysteinyldopa to pheomelanins
摘要:
Under biologically relevant conditions, oxidation of 5-S-cysteinyldopa (1) to pheomelanins proceeds through the formation of the 1,4-benothiazine 7 along with the 3-carboxy analogue 6 in much smaller amounts, as evidenced by isolation of the reduced forms 5 and 4 and by deuterium labelling experiments.
Oxidation of natural and synthetic pheomelanins with alkaline H2O2 at room temperature led to the formation of a major product (up to 25% yield w/w) which was identified as the novel 2-carboxy-4-hydroxy-6-(2-amino-2-carboxyethyl)benzothiazole (6). Copyright (C) 1996 Published by Elsevier Science Ltd
Photochemical ring contraction of dihydro-1,4-benzothiazines
The pheomelanin precursor 1a and the related dihydro-1,4-benzothiazines 1b–f undergo ringcontraction upon irradiation with pyrex-filtered UV light to give 2-methylbenzothiazoles 2a–f in good yields.
Under biologically relevant conditions, oxidation of 5-S-cysteinyldopa (1) to pheomelanins proceeds through the formation of the 1,4-benothiazine 7 along with the 3-carboxy analogue 6 in much smaller amounts, as evidenced by isolation of the reduced forms 5 and 4 and by deuterium labelling experiments.