Efficient removal of N-benzyloxycarbonyl group by a ‘push–pull’ mechanism using thioanisole–trifluoroacetic acid, exemplified by a synthesis of Met-enkephalin

The N-benzyloxycarbonyl group can be smoothly cleaved under mild conditions, using thioanisole–trifluoroacetic acid, which can deprotect O-benzyltyrosine without the formation of O-to-C rearrangement products; this deblocking method was successfully applied to the synthesis of Met-enkephalin.