REGIOSPECIFIC BROMINATION OF 3-METHYLINDOLES WITH NBS AND ITS APPLICATION TO THE CONCISE SYNTHESIS OF OPTICALLY-ACTIVE UNUSUAL TRYPTOPHANS PRESENT IN MARINE CYCLIC-PEPTIDES

A regiospecific bromination of substituted 3-methylindoles at either t he C(3) alkyl moiety or the C(2) position was achieved via a free radi cal bromination or electrophilic process, respectively. The regiospeci ficity of the bromination could be controlled by variation of both the substituent and the N(1) protecting group on the indole ring. In addi tion, enantiospecific syntheses of 5-methoxytryptophan (20) and 5-hydr oxy-6-chlorotryptophan (21c) as well as concise syntheses of optically active 2-bromotryptophan ethyl esters 26a,b or their substituted deri vatives in three steps from bifunctional dibromoindoles were achieved via the above regiospecific process.