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Note | Regular issue | Vol 65, No. 6, 2005, pp.1455-1459
Published online, 24th March, 2005
DOI: 10.3987/COM-05-10380
An Improved Synthesis of Optically Pure (R)-4-Bromo-N-methyl-1-tosyltryptophan Derivative, a Key Intermediate in the Synthesis of Ergot Alkaloids

Yuusaku Yokoyama,* Ryoko Hara, Nahoko Kato, Yasuoki Murakami, and Hiroaki Okuno

*School of Pharmaceutical Sciences, Toho University, 2-2-1, Miyama, Funabashi, Chiba 274-8510, Japan

Abstract

Optically pure (R)-N-Boc- or (R)-Cbz-4-bromo-N-methyl-1-tosyltryptophan methyl ester (11a or b) was synthesized in 2 steps from (R)-N-acetyl-4-bromo-1-tosyltryptophan methyl ester (7) by simultaneous N-methylation and deacetylation using methyl trifluoromethanesulfonate (TfOMe) in the presence of 2,6-di-tert-butyl-4-methylpyridine (DTBMP).