Painting argyrins blue: Negishi cross-coupling for synthesis of deep-blue tryptophan analogue β-(1-azulenyl)-l alanine and its incorporation into argyrin C

Publication date: Available online 26 March 2018
Source:Bioorganic & Medicinal Chemistry
Author(s): Erik Stempel, Robert Franz-Xaver Kaml, Nediljko Budisa, Markus Kalesse
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.

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