Synthesis and Structure–Activity Relationship of Phosphonate Esters with (<i>S</i>)-Cinerolone and (<i>S</i>)-Jasmololone as Irreversible Inhibitors of the GDSL Esterase/Lipase TcGLIP to Study Pyrethrin Biosynthesis

TcGLIP, a GDSL esterase/lipase family enzyme found widely across species, synthesizes natural insecticides pyrethrins with (1<i>R</i>,3<i>R</i>)-chrysanthemoyl CoA and (<i>S</i>)-rethrolones as substrates in the Dalmatian Daisy Tanacetum cinerariifolium. We previously reported that alkyl- or benzyl-substituted phosphonate esters with (<i>S</i>)-pyrethrolone blocked TcGLIP at nanomolar ranges, but the mechanism of enzyme-substrate interactions remains elusive. Notably, it is unclear whether the conjugated diene of (<i>S</i>)-pyrethrolonyl moiety is essential for TcGLIP inhibition and whether such probes are effective in blocking pyrethrin biosynthesis for other pyrethrum plant species capable of cinerin I/II and jasmolin I/II biosynthesis but not pyrethrin I/II. In this study, <i>n</i>-pentyl- or <i>n</i>-octyl-substituted phosphonate esters were synthesized with either (<i>S</i>)-cinerolone or (<i>S</i>)-jasmololone lacking the conjugated diene as mixtures of (<i>S</i>)_p, (<i>S</i>)_c and (<i>R</i>)_p, (<i>S</i>)_c diastereomers, then TcGLIP inhibition was evaluated. These compounds blocked TcGLIP in the order of (<i>S</i>)-pyrethrolonyl > (<i>S</i>)-cinerolonyl > (<i>S</i>)-jasmololonyl esters regardless of whether the alkyl chain moiety was <i>n</i>-pentyl or <i>n</i>-octyl. The (<i>S</i>)_p, (<i>S</i>)_c isomers were more potent inhibitors than the corresponding (<i>R</i>)_p, (<i>S</i>)_c isomers for the <i>n</i>-pentyl series compounds. In contrast, the inverse was the case for the <i>n</i>-octyl series compounds. These results contribute to understanding TcGLIP recognition mechanisms of the rethrolone alkyl chain and phosphorus atom and assist in probe design to influence pyrethrin biosynthesis in Asteraceae plants.