Syntheses of substituted L- and D-tryptophans.

A convenient enzymatic synthesis of l-halotryptophans

“…9 Two notable exceptions are the elegant, but by no means atom efficient, palladium-mediated heteroannulation of a Scho ¨llkopf chiral auxiliary, 10 and the technically specialised electrochemical oxidation of proline to 5-hydroxyproline followed by Fischerindolesynthesis. 11 Incontrastthedirectenzymaticalkylation of indole with serine constitutes a direct and potentially efficient approach and has been demonstrated to be useful in the preparation of a number of tryptophan analogues. 12 This approach has not been widely adopted because of the need to purify tryptophan synthase.…”

Total Synthesis without Protection: Three‐Step Synthesis of Optically Active Clavicipitic Acids by a Biomimetic Route

“…We thought that the lower yield in run 2 compared to run 3 might be due to decomposition of 2 prior to the formation of dl-N-acetylserine (dl-13). Therefore, dl-13 was prepared in situ by reaction with Ac 2 O at a lower temperature (45°C, 5 h) prior to the addition of 4-bromoindole (7). The yield from this reaction was an improved 73% (run 4).…”

“…The N-acetyl group can be used in a kinetic resolution to obtain optically active 4-bromotryptophan (S-8); treatment of N-acetylamino acids with acylase for this purpose is well established [7] as a practical and economical method in amino acid synthesis. N-Acetyl-4-bromotryptophan (dl-12b) [8] was treated with commercially available Aspergillus acylase at pH 7.5 for 3 days at 37°C.…”

A Facile Two‐Step Synthesis of Novel Ring‐A Double Substituted Tryptophan Building Blocks (IV) for Combinatorial Chemistry.

“…In a third approach 5-hydroxy derivatives of tryptophan were prepared via a Fischer indole ring formation mediated by isolated intermediate hydrazones obtained from the condensation of substituted phenylhydrazines and aldehyde derivatives of protected glutamic acid. [15][16][17] Overall, these methods suffer from a number of disadvantages. Some are limited to tryptophan analogs with no alkyl substituents on the ring A, 9,[11][12][13] as the presence of such alkyl substitutents will likely promote a non-selective bromination and a mixture of di-halogenated indole products will be obtained.…”