A new strategy for aromatic ring alkylation in cylindrocyclophane biosynthesis

Cylindrocyclophane biosynthesis involves an unexpected halogenated intermediate arising from chlorination of an unactivated carbon center by a halogenase, followed by dimerization through stereospecific enzymatic alkylation of resorcinol aromatic rings. Alkylation of aromatic rings with alkyl halides is an important transformation in organic synthesis, yet an enzymatic equivalent is unknown. Here, we report that cylindrocyclophane biosynthesis in Cylindrospermum licheniforme ATCC 29412 involves chlorination of an unactivated carbon center by a novel halogenase, followed by a previously uncharacterized enzymatic dimerization reaction featuring sequential, stereospecific alkylations of resorcinol aromatic rings. Discovery of the enzymatic machinery underlying this unique biosynthetic carbon–carbon bond formation has implications for biocatalysis and metabolic engineering.