Pyridoxal 5'-Phosphate-Dependent Enzymatic Decarboxylative Annulation.

Pyridoxal 5'-phosphate (PLP)-dependent enzymes are among the most versatile biocatalysts, yet transformations involving the Cγ-nucleophilic vinylglycine quinonoid (VGQ) intermediate remain exceptionally rare. Understanding the untapped reactivity of VGQ could open new avenues for developing PLP-dependent biocatalysts. Here, we establish a biocatalytic platform that artificially accesses and exploits the reactivity of this high-energy intermediate. By reprogramming SphA, a PLP-dependent enzyme that natively catalyzes decarboxylative Claisen condensation, to generate VGQ in situ through facile decarboxylation of vinylaminomalonate, we enable a decarboxylative [3 + 2] annulation between vinylaminomalonate and electron-deficient alkenes. Crystallographic, computational, and mutagenesis studies reveal the key mechanistic features underlying this abiotic transformation. Our findings demonstrate the latent [3 + 2] annulating potential of VGQ and expand the catalytic repertoire of PLP-dependent enzymes, establishing a new strategy for the enzymatic construction of complex carbocyclic architectures.