Biomimetic Synthesis of Oleocanthal, Oleacein, and Their Analogues Starting from Oleuropein, A Major Compound of Olive Leaves.

Oleocanthal and oleacein are known for a wide range of beneficial activities in human health and the prevention of diseases. The inability to isolate significant and pure amounts of these natural compounds and their demanding synthesis lead to the development of an efficient, five-step, three-pot procedure. The synthesis is performed by a convenient biomimetic approach, starting from oleuropein, an abundant raw material in olive leaves, through the mixed anhydride of oleoside. The method is stereocontrolled and provides an efficient approach to the synthesis of various oleocanthal analogues; thus, a small library of four compounds was prepared with 35-45% overall yield.

New semi-synthetic analogs of oleuropein show improved anticancer activity in vitro and in vivo.

Oleuropein is a glucosylated seco-iridoid present in olive fruits and leaves. Due to its broad spectrum of biological activities, including anticancer properties, oleuropein has attracted scientific attention for the past 20 years. The promising antiproliferative activity of an olive leaf extract enriched in oleuropein against a series of human cancer cell lines, prompted us to proceed with the semi-synthesis of 51 analogs of oleuropein. Following their initial screening against the estrogen receptor negative breast cancer cell line SKBR3, 7 analogs were shown to display significant cytotoxicity and were further tested against 6 additional solid tumor-derived and leukemic cell lines. The analog with the most promising antitumor activity (24) was selected for more detailed studies. 24 was non-toxic to peripheral blood mononuclear cells derived from healthy blood donors when tested at concentrations close to its half maximal inhibitory concentration. In vivo administration of 24 in melanoma-bearing mice resulted in reducing tumor size in a dose-dependent manner and in inducing anti-melanoma-reactive immune responses. Our results suggest that analog 24, emerging from the initial structure of oleuropein, represents a promising lead structure for further optimization.