Reduction of emodin by sodium dithionite resulted in
the formation
of two tautomeric forms of emodin hydroquinone. Subsequent conversion
by the short-chain dehydrogenase/reductase (SDR) MdpC into the corresponding
3-hydroxy-3,4-dihydroanthracen-1(2<i>H</i>)-one implies
that deoxygenation is the first step in monodictyphenone biosynthesis.
Implications for chrysophanol formation as well as reaction sequences
in the related xanthone, ergochrome, and bianthraquinone biosyntheses
are discussed