Discovery and characterisation of catedehas A–C, a new class of antioxidant <i>α</i>,<i>β</i>-dehydroamino acid derivatives

Dehydroamino acids are a class of noncanonical unsaturated amino acids commonly found in various naturally occurring peptides and proteins. In this study, we successfully cloned and heterologously expressed the <i>cda</i> biosynthetic gene cluster from <i>Streptomyces nitrosporeus</i> ATCC 12769 in <i>Streptomyces lividans</i> TK24, leading to the identification of three <i>α,β</i>-dehydroamino acid derivatives, designated as catedehas A–C (<b>1</b>–<b>3</b>). Among these, compound <b>2</b>, although previously reported, lacked any detailed characterisation data. Their structures were elucidated by high-resolution electrospray ionisation mass spectrometry, 1D and 2D nuclear magnetic resonance spectroscopy, along with other spectroscopic techniques. Compounds <b>1</b>–<b>3</b> exhibited remarkable antioxidant activity in DPPH· free radical scavenging assay, with IC₅₀ values of 27.52, 12.51, and 8.32 μM, respectively.