Discovery and Characterization of a Terpene Biosynthetic Pathway featuring a Norbornene-forming Diels-Alderase

Abstract

Pericyclases, enzymes that catalyze pericyclic reactions, form an expanding family of enzymes that have biocatalytic utility. Despite the increasing number of pericyclases discovered, the Diels-Alder (DA) cyclization between a cyclopentadiene and an olefinic dienophile to form norbornene, which is among the best-studied cycloadditions in synthetic chemistry, has surprisingly no enzymatic counterpart to date. Here we report the discovery of a pathway featuring a norbornene synthase SdnG for the biosynthesis of sordaricin-the terpene precursor of antifungal natural product sordarin. Full reconstitution of sordaricin biosynthesis revealed a concise oxidative strategy used by Nature to transform an entirely hydrocarbon precursor into the highly functionalized substrate of SdnG for intramolecular Diels-Alder (IMDA) cycloaddition. SdnG generates the norbornene core of sordaricin and accelerates this reaction to suppress host-mediated redox modifications of the activated dienophile. Findings from this work expand the scopes of pericyclase-catalyzed reactions and P450-mediated terpene maturation.

Exploring the versatility of pentafulvene–maleimide cycloaddition as a ligation strategy: buffer and pH effects

“…A relevant area of study is enzymatic reactions (e.g., Diels-Alderases), where interactions between various functional groups influence the rate and endo/exo selectivity of DAC reactions. [38][39][40][41] Practical and theoretical experiments have shown that the enzymatic reaction proceeds via an asynchronous Diels-Alder mechanism by changes to the structural and electronic properties of the transition state. 39,40 Therefore, a possible explanation for the variation in rate and endo/exo stereoselectivity of the DAC reactions between 1 and 2 in different buffers (Table 2) are interactions (e.g., H-bonding) between the functional groups on the buffering agents and the reactants that influence and favour the stabilisation of the endo transition-state.…”