Mechanistic studies on the biomimetic reduction of tetrahydroxynaphthalene, a key intermediate in melanin biosynthesis

1,3,6,8-Tetrahydroxynaphthalene (T4HN) is an aromatic polyketide, serving as a general precursor of fungal melanin. Melanin biosynthesis involves two consecutive deoxygenations of T4HN, consisting of the reduction of a phenolic carbon followed by dehydration. The first reduction to produce scytalone was studied in a biomimetic reduction with sodium borohydride. The reduction required a strong alkaline condition, leading to the tautomerization of T4HN to a reactive species whose structure was clarified bit NMR spectroscopy.