Alkyne bridged alpha-amino acids by palladium mediated coupling of alkynes with N-t-Boc-4-iodophenylalanine methyl ester

The Heck reaction of trimethyisilylacetylene with N-t-Boc-4-iodo-L-phenylalanine methyl est er gives N-t-Boc-4-ethynyl-L-phenylalanine methyl ester (2). Coupling of 2 with different alkynes yields alkyne bridged linear amino acid esters 3- 5. Also tripodal and tetrapodal amino acid esters 10 and 11 were prepared by this approach. All compounds have been obtained in enantiomerically pure form. The protecting groups were removed by standard methods to yield the free amino acids as hydrochlorides. (C) 1997, Elsevier Science Ltd.