L-phenylalanine was transformed in three steps into tert-butyl (S)-butyl(1-((2-cycloheptylethyl)amino)-1-oxo-phenylpropane-2-yl)carbamate, which was utilized in further syntheses. Two different approaches were tried in order to convert the carbamate into a cyclic five-membered aminal for the synthesis of precursors to N-heterocyclic carbenes. The first route involved direct cyclization/reduction and the second one cyclization with a strong base and subsequent reduction of the resulting hydantoin. The Boc protecting groups from the starting carbamate was also removed to give an amine analogous to the already known efficient tryptophan-based butyrylcholinesterase inhibitor. The inhibitory activity of the amine has been tested on human butyrylcholinesterase (hBChE).
Keywords: aminal, N-heterocyclic carbene, butyrylcholinesterase, phenylalanine