(4S,8R)-2,13,16,20-tetrahydroxy-7,9-dioxapentacyclo[10.8.0.0(3,10).0(4,8).0(14,19)]icosa-1(12),2,5,10,13,16,19-heptaen-18-one + NADPH + H(+) = (4S,8R,16R)-2,13,16,20-tetrahydroxy-7,9-dioxapentacyclo[10.8.0.0(3,10).0(4,8).0(14,19)]icosa-1(12),2,5,10,13,19-hexaen-18-one + NADP(+) — reaction