HETEROCYCLES

Heterocycles has a pay-per-view service for Non-subscribers.
You will be able to directly purchase the full text article through PayPal.
Your purchased Paper can be downloaded after the payment is completed.
An e-mail will be sent the URL to download the paper.
If you have any questions, please contact: purchase@heterocycles.com

Price: ¥ 4,400 (Yen only)
Period: This Article can be accessed for 7 days.

■ α-Alkyltryptohans

Miguel F. Braña, Mercedes Garrido, María L. López Rodríguez, and M. José Morcillo

*Departamento de Química Orgánica I., Facultad de Química, Universidad Complutense de Madrid, Ciudad Universitaria, E-28040 Madrid, Spain

Abstract

A study of three direct methods for the synthesis of α-alkyl α-amino acids has been applied to the preparation of α-alkyltryptophan esters. Reaction of N_b-benzylidene-L -tryptophan methyl esters 3 with tetrabutyl-ammonium hydrogen sulfate and methyl or ethyl iodide (phase-transfer method) gives α-methyl and α-ethyltryptophan methyl esters 6a,b in poor yield with complete racemization. Reaction of L-tryptophan 1 with dimethylformamide dimethyl or diethyl acetal followed by treatment of 8a,b with LDA and methyl iodide (Fitt and Gschwend method) gives rise to the formation of α,N_a -dimethyl-N_b - dimethylsminamethylenetryptophan methyl or ethyl esters hydriodide 9 a,b . Treatment of 9a or 9b with aqueous acid, under mild conditions, fails to hydrolyze the imine functionality. Reaction of 3 with LDA and methyl or ethyl iodide (Bey and Vevert method) followed by hydrolysis provides α-methyl and α-ethyltryptophan methyl esters 6a,b. By carrying out this procedure with isopropyl, benzyl and allyl iodide or bromide the corresponding α-alkyl esters are not obtained.