20-hydroxy-(5Z,8Z,11Z,14Z)-eicosatetraenoate + reduced [NADPH--hemoprotein reductase] + O2 = 20-hydroxy-8,9-epoxy-(5Z,11Z,14Z)-eicosatrienoate + oxidized [NADPH--hemoprotein reductase] + H2O + H(+) — reaction