Non-heme-dependent dioxygenase that catalyzes the oxidative epoxidation of (S)-2-hydroxypropylphosphonate into (1R,2S)-epoxypropylphosphonate, the final step in the biosynthesis of fosfomycin antibiotic. (S)-2-hydroxypropylphosphonate + H2O2 = (1R,2S)-epoxypropylphosphonate + 2 H2O Binds 1 Fe(2+) ion per subunit. Antibiotic biosynthesis; fosfomycin biosynthesis. Homotetramer. Phosphinothricin tripeptide (PTT) herbicide and fosfomycin antibiotic biosynthesis pathways share early steps starting with phosphoenolpyruvate before the pathways diverge after formation of 2-hydroxyethylphosphonate (HEP). HppE is involved in fosfomycin biosynthesis after divergence of the 2 pathways. Belongs to the non-heme iron-dependent dioxygenase family.