Rdc2 is a flavin-dependent halogenase from Pochonia chlamydosporia. Through the introduction of a His6-tag to both the N- and C-termini, the isolation yield of Rdc2 from Escherichia coli using Ni-NTA affinity chromatography was increased by three-fold. In vitro reaction of Rdc2 and a flavin reductase (Fre) with seven different hydroxyquinolines revealed that 3-hydroxyquinoline (3), 5-hydroxyquinoline (5), 6-hydroxyquinoline (6), and 7-hydroxyquinoline (7) can be specifically halogenated. These products were prepared by incubating the corresponding substrates with IPTG-induced E. coli BL21(DE3)/Rdc2. They were respectively characterized as 3-hydroxy-4-chloroquinoline (3a), 5-hydroxy-6-chloroquinoline (5a), 5-chloro-6-hydroxyquinoline (6a), and 7-hydroxy-8-chloroquinoline (7a) by NMR and MS analyses. This work represents the first enzymatic preparation of chlorohydroxyquinolines and provides a ‘green’ method to synthesize this group of medicinally important compounds.
Xu, Fuchao; Merkley, Amanda; Yu, Dayu; and Zhan, Jixun, "Selective Biochlorination of Hydroxyquinolines by a Flavin-Dependent Halogenase" (2010). Biological Engineering Faculty Publications. Paper 146.