Synthesis of enantiomerically pure 4-alkylsubstituted tryptophan derivatives by a combination of organometallic reactions with enantioselective enzymatic transformations
The synthesis of enantiomerically pure 4-substituted tryptophans12 is described. Key steps are i) the introduction of an alkyl substituent into the 4-position of the indole via regioselective lithiation of N-TIPS protected gramine and ii) the enantioselective saponification of the phenyl acetamides of 4-substituted tryptophans by the enzyme penicillin G acylase.