Naturally occurring quinones. Part XV. Biogenesis of the anthraquinones in Rubia tinctorum L. (madder)

Nineteen anthraquinones, all substituted in one benzenoid ring only, were isolated from mature plants of R. tinctorum. One-year old plants yielded nordihydrolapachenole and four quinones, alizarin, purpurin, rubiadin, and pseudopurpurin. All four incorporated [2-14C]mevalonate into the substituted ring and into the side-chain of pseudopurpurin and rubiadin. A partial biosynthetic pathway is suggested.