Trichlorination by a single cyanobacterial halogenase in the biosynthesis of lebomboamide A

Abstract

Halogenation is a widely used strategy, both in nature and medicinal chemistry, to modulate the properties of small molecules. Cyanobacteria are a rich source of halogenases that act regio- and stereoselectively on sp3-hybridized carbon centers, which have been reported to catalyze the incorporation of one or two halogen atoms into each substrate molecule. In this work, we report trichlorinated natural products – lebomboamides – from the cyanobacterium Nostoc sp. LEGE 12454. Lebomboamide A (1) was isolated and characterized by NMR spectroscopy. The three chlorine substituents were found to be located in a γ-chloro,δ-gem-dichloro acyl moiety. A candidate biosynthetic gene cluster (BGC) for lebomboamides (lbb) was identified, encoding a single non-heme Fe(II)/α-ketoglutarate-dependent halogenase (LbbB). In vitro assays demonstrated that this halogenase can perform the triple halogenation of fatty acyl moieties. LbbB is the first reported enzyme capable of performing triple halogenation of sp3-hybridized carbons. We additionally found that enzymes closely related to LbbB, including the previously characterized dichlorinase HctB, can also carry out triple halogenation in vitro, suggesting that this group of halogenases can be fine-tuned for different catalytic outcomes. Halogenation is crucial in modulating small molecule properties, yet enzymes capable of triple halogenation remain elusive. Here, the authors identify a halogenase from the cyanobacterium Nostoc sp. LEGE 12454 capable of triple halogenation on sp3-hybridized carbons.