9,10-dihydroxy-7-methoxy-3-(2-oxopropyl)-1H-benzo[g]isochromen-1-one + NADPH + O2 + H(+) = methyl 2-[(3S)-9,10-dihydroxy-7-methoxy-1-oxo-1H,3H,4H-naphtho[2,3-c]pyran-3-yl]acetate + NADP(+) + H2O — reaction