Involved in the biosynthesis of syringomycin E, a cyclic lipodepsinonapeptide toxin with phytotoxic activity (PubMed:16002467, PubMed:16528784, PubMed:19245217). Catalyzes the chlorination of L-Thr to 4-Cl-L-Thr when the amino acid is tethered via a thioester linkage to a covalently bound phosphopantetheine cofactor of the carrier protein SyrB1 (L-Thr-S-SyrB1), in a reaction that requires oxygen, chloride ions, ferrous iron and 2-oxoglutarate (PubMed:16002467, PubMed:16528784, PubMed:19245217). In vitro, can catalyze tandem chlorinations at the gamma-position of the threonyl-S-protein substrate (PubMed:16528784). Can also brominate L-Thr-S-SyrB1 in reactions performed with excess sodium bromide, but a preference for chloride versus bromide by a factor of 180 can be estimated by comparing the peak intensities (PubMed:16528784). In addition, in the presence of the nitrogenous anions NO2(-) or N3(-), SyrB2 can direct aliphatic nitration and azidation reactions by the same mechanism as the native halogenation reaction (PubMed:24463698). 2-oxoglutarate + chloride + H(+) + L-threonyl-[peptidyl-carrier protein] + O2 = 4-chloro-L-threonyl-[peptidyl-carrier protein] + CO2 + H2O + succinate Binds 1 Fe(2+) ion. The complete trimodular substrate, with carrier protein (SyrB1), covalently attached PPant cofactor, and thioester-appended amino acid, is required for substrate triggering of rapid chloroferryl intermediate formation. Iron is coordinated by two histidines and one chloride ligand, in contrast to the two-histidine/one carboxylate facial triad of other mononuclear non-haem iron enzymes. The remaining iron coordination sites are occupied by the 2-oxoglutarate and a water molecule. The ability to install nitrogenous functional groups, in particular the azido group, onto aliphatic carbon centers could enable new methods in the field of chemical biology. Belongs to the PhyH family.