Methyl 5,7-dihydr­oxy-2,2,9-trimethyl-6,11-dioxo-6,11-dihydro-2H-anthra[2,3-b]pyran-8-carboxyl­ate

The title compound, C22H18O7, also known as laurentiquinone B, is a new anthraquinone which was isolated from Vismia laurentii, a Cameroonian medicinal plant. The asymmetric unit contains two independent mol­ecules. Each of them contains four fused rings, three of which are coplanar and typical of anthracene, while the heterocyclic rings adopt envelope conformations. Intra­molecular O—H⋯O hydrogen bonds result in the formation of two planar rings, which are also almost coplanar with the adjacent rings. In the crystal structure, inter­molecular O—H⋯O and C—H⋯O hydrogen bonds link the mol­ecules and a π–π contact is also present [centroid-centroid distance = 3.967 (3) A].