Formation and Reactions of the Cyclic Tautomers of Tryptophans and Tryptamines. VII. Hydroxylation of Tryptophans and Tryptamines

The 5-hydroxytryptophan derivative 12 was prepared in 60% yield from the tryptophan derivative 8 by selective oxidation of the cyclic tautomer 9 with Fremy's salt or Pb (OAc)4-CF3COOH to the p-quinoneimine 10, followed by reduction and ring-opening. By analogous oxidation, serotonin was prepared from tryptamine. On the other hand, the oxidation of the Na-acetyl-cyclic tautomers (16 and 22) with Pb (OAc)4-CF3COOH followed by methylation gave the 5-and 6-methoxy derivatives (17, 18, 23, and 24) in 20-40% yields. These compounds were readily converted to the 5-and 6-methoxytryptophan derivatives (20, 21) by acid treatment. These methods are the first practical hydroxylation procedures to be reported for tryptophans.