2 Results and Discussion
2.1 Objectives
Hederagonic acid was found to be a suitable starting material for the
synthesis of polyhydroxylated triterpenoids. Nevertheless, hederagonic acid
is very expensive and has limited commercial availability. Hederagonic
acid can be synthetically accessed from oleanolic acid, a cheap and readily
available natural product. However, the to date only reported synthesis of
hederagonic acid requires 9 steps, starting from oleanolic acid, and utilises
stoichiometric amounts of palladium for the C–H oxidation at position C-23
(Section 1.1.3). Addressing these drawbacks, this work aims to provide a
shorter and cheaper synthesis of hederagonic acid to enhance the accessibility
of hederagonic acid as a starting material for semisyntheses. Furthermore,
synthetic intermediates that can serve as a starting point to access further
polyhydroxylated triterpenoids were targeted.
HO
H
H
OH
O
H
O
H
H
OH
O
H
HO
H
Catalytic C–H oxidation
Hederagonic acid (1)
Oleanolic acid (5)
Scheme 2.1: Concise synthesis of hederagonic acid (1) via catalytic C–H oxidation.
© The Editor(s) (if applicable) and The Author(s), under exclusive license to
Springer Fachmedien Wiesbaden GmbH, part of Springer Nature 2020
C. Knittl-Frank, A Concise Semisynthesis of Hederagonic Acid, BestMasters,
https://doi.org/10.1007/978-3-658-30011-1_2