Synthetic studies of polyhydroxynaphthoquinones

Abstract

Although many quinoid pigments are known, until recently only six naphthoquinone pigments had been isolated from animals and identified. However in 1966, Moore, Singh and Scheuer reported the isolation of over thirty different pigments from the sea urchins Echinothrix diadema Linn. and E. calamaris Pallis. In addition to five known compounds, eleven new pigments were identified. Several of these pigments were juglone derivatives containing hydroxyl and acetyl functions. The synthesis of only three acetyljuglone derivatives has been described previously. This paucity of data showed the need for further work in this area. For this reason and in order to facilitate structure proof of several new pigments, the introduction of hydroxyl and acetyl groups into juglone and several of its derivatives was investigated. As a result of this work the structures of three pigments (i, ii, iii) were confirmed, but a fourth compound (iv) did not display identical properties with those of the natural pigment. In addition to the synthesis of compounds i-iv, five new juglone derivatives (v-ix) were prepared. Compounds v-ix have not yet been reported as naturally occurring substances. Investigation of new methods for the synthesis of juglone and naphthazarin derivatives was unsuccessful.