Rhamnus californica and Umbellularia californica were
obtained from the University of California at Berkeley
Botanical Garden (UCBBG). Specimens were authenticated
by Dr. Holly Forbes, curator of the UCBBG. Voucher specimens
for each species (50.1622 and 71.0162) have been
deposited at the UC Berkeley Herbarium. Leaves and bark
were separated and oven dried after which they were
grinded into fine powder or shavings. Thimbles were
filled with dried leaf or bark material (30 g) and extracted
using a Soxhlet apparatus. The plant materials
were successively extracted with hexanes, dichloromethane,
and methanol (2 × 100 ml for 24 h each). The
resulting extracts were filtered, concentrated under reduced
pressure, and kept at 4 °C.