Synthesis of beta-(1-azulenyl)-L-alanine as a potential blue-colored fluorescent tryptophan analog and its use in peptide synthesis.

Acetyl-beta-(1-azulenyl)-D,L-alanine has been synthesized in high overall yield by the malonic ester condensation procedure, and the racemate has been enzymatically resolved with acylase I from Aspergillus melleus. The enantiomerically pure L-amino acid is of interest as a blue-colored fluorescent tryptophan analog. The bioactivity data of a heptagastrin analog containing it suggests that the planar aromatic azulene moiety may indeed mimic the tryptophan side chain to some extent, and the spectral properties of the azulene moiety makes beta-(1-azulenyl)-L-alanine of potential value as a UV and fluorescence probe in synthetic peptides, and possibly even in proteins if bioincorporation succeeds with chemically misacylated tRNAs.