Cover Picture (Angew. Chem. Int. Ed. Engl. 5/1991)

The title picture shows leaves of the ginkgo tree. An extract obtained from these leaves is used to improve blood circulation in the brain, to elevate blood sugar level, and to increase metabolism in the brain. It contains, among other substances, ginkgolide B, whose formula is shown at the center of the picture. The total synthesis of this highly complex hexacyclic C 20 trilactone by E. J. Corey et al., reported in 1988, marked a new, much admired high point in natural product synthesis. In 1990, Corey was awarded the Nobel Prize in chemistry for his contributions to organic synthesis. His scientific career and the development of his new approaches to organic synthesis, especially the use of computers in synthetic planning and the introduction of new synthetic techniques, is the subject of his Nobel Lecture beginning on page 455. (The picture of the ginkgo tree leaves was provided by Dr. Willmar Schwabe Arzneimittel. The formula was taken from The Logic of Chemical Synthesis (Wiley, New York 1989, p. 221) by E. J. Corey and X.‐M. Cheng.)