Precursor-Directed Biosynthesis and Biological Testing of <i>omega</i>-Alicyclic- and <i>neo</i>-Branched Tunicamycin <i>N</i>‑Acyl Variants

Tunicamycins (TUNs) are <i>Streptomyces</i>-derived natural products, widely used to block protein <i>N</i>-glycosylation in eukaryotes or cell wall biosynthesis in bacteria. Modified or synthetic TUN analogues that uncouple these activities have considerable potential as novel mode-of-action antibacterial agents. Chemically modified TUNs reported previously with attenuated activity on yeast have pinpointed eukaryotic-specific chemophores in the uridyl group and the <i>N</i>-acyl chain length and terminal branching pattern. A small molecule screen of fatty acid biosynthetic primers identified several novel alicyclic- and <i>neo</i>-branched TUN <i>N</i>-acyl variants, with primer incorporation at the terminal <i>omega</i>-acyl position. TUNs with unique 5- and 6-carbon ω-cycloalkane and ω-cycloalkene acyl chains are produced under fermentation and in yields comparable with the native TUN. The purification, structural assignments, and the comparable antimicrobial properties of 15 of these compounds are reported, greatly extending the structural diversity of this class of compounds for potential medicinal and agricultural applications.