An Efficient Method of Synthesizing Optically Pure N-Boc-4-bromo-N-methyl-1-tosyl-D-tryptophan Methyl Ester, a Key Intermediate in the Synthesis of Optically Active Ergot Alkaloids
Optically pure N-Boc-4-bromo-N-methyl-1-tosyl-D-tryptophan methyl ester (D-4), a key intermediate in the synthesis of optically active ergot alkaloids such as chanoclavine-I (7) and costaclavine (8), was prepared from N-acetyl-4-bromo-D-tryptophan (D-ll) obtained from 4-bromoindole (9) and DL-serine (10) in two steps.