%0 Journal Article
%T Painting argyrins blue: Negishi cross-coupling for synthesis of deep-blue tryptophan analogue β-(1-azulenyl)-l alanine and its incorporation into argyrin C.
%A Stempel E
%A Kaml RF
%A Budisa N
%A Kalesse M
%J Bioorg Med Chem
%V 26
%N 19
%D 10 2018 15
%M 29729984
%F 3.461
%R 10.1016/j.bmc.2018.03.037
%X The argyrins are a family of non-ribosomal peptides that exhibits different biological activities through only small structural changes. Ideally, a biologically active molecule can be tracked and observed in a variety of biological and clinical settings in a non-invasive manner. As a step towards this goal, we report here a chemical synthesis of unnatural deep blue amino acid β-(1-azulenyl)-l alanine with different fluorescence and photophysical properties, which allows a spectral separation from the native tryptophan signal. This might be especially useful for cell localization studies and visualizing the targeted proteins. In particular, the synthesis of β-(1-azulenyl)-l alanine was achieved through a Negishi coupling which proved to be a powerful tool for the synthesis of unnatural tryptophan analogs. Upon β-(1-azulenyl)-l alanine incorporation into argyrin C, deep blue octapeptide variant was spectrally and structurally characterized.