Isagarin, a new type of tetracyclic naphthoquinone from the roots of pentaslongiflora

A new type of tetracyclic naphthoquinone, named isagarin (1), was isolated from the hexane extract of the roots of Pentas longiflora. On the basis of spectral and X-ray diffraction analysis this compound was identified as 1,4-epoxy-4-methyl-1,2,4, 5-tetrahydronaphtho[2.3-d]oxepin-6,11-dione.