The South African tree Combretum caffrum (Combretaceae) has been found to contain a series of biosynthetically related substances that significantly inhibit growth of the US. National Cancer Institute's murine P-388 lymphocytic leukemia cell line (PS system). Some of these dihydrostilbenes, cis-stilbenes, phenanthrenes, and dihydrophenanthrenes, especially combretastatin A-1 and A-4, were also found to strongly inhibit tubulin polymerization. We now report the isolation and structural elucidation of an unexpected and unusual macrocyclic lactone designated combretastatin D-1 (1) with PS cell line activity corresponding to ED50 3.3 μg/mL. The nature of the reactive oxygen in olefin epoxidation is a subject of much debate. We wish to report the epoxidation of an olefin by atomic oxygen on silver under ultrahigh vacuum. Norbornene (1) reacts with atomic oxygen on Ag(110) to form norbornene oxide (2) at 310 K during temperature-programmed reaction. The importance of this observation is 3-fold: first, atomic oxygen is proved to easily epoxidize an olefin on a silver surface; second, ethylene and atomic oxygen do not react when coadsorbed on silver under ultrahigh vacuum because ethylene's desorption activation energy is lower than its reaction activation energy with atomic oxygen; finally, epoxidation of olefins on silver is facilitated by the absence of an acidic hydrogen on the olefin.