Cephalotaxus Alkaloids
Résumé
Cephalotaxus alkaloids represent a family of plant secondary metabolites known for
60 years. Significant activity against leukemia in mice was demonstrated for extracts
of Cephalotaxus. Cephalotaxine (CET) (1), the major alkaloid of this series was isolated
from Cephalotaxus drupacea species by Paudler in 1963. The subsequent discovery of
promising antitumor activity among new Cephalotaxus derivatives reported by Chinese,
Japanese, and American teams triggered extensive structure elucidation and biological
studies in this family. The structural feature of this cephalotaxane family relies mainly on
its tetracyclic alkaloid backbone, which comprises an azaspiranic 1-azaspiro[4.4]nonane
unit (rings C and D) and a benzazepine ring system (rings A and B), which is linked by its
C3 alcohol function to a chiral oxygenated side chain by a carboxylic function alpha to a
tetrasubstituted carbon center. The botanical distribution of these alkaloids is limited to
the Cephalotaxus genus (Cephalotaxaceae). The scope of biological activities of
the Cephalotaxus alkaloids is mainly centered on the antileukemic activity of homoharringtonine (HHT) (2), which in particular demonstrated marked benefits in the
treatment of orphan myeloid leukemia and was approved as soon as 2009 by European
Medicine Agency and by US Food and Drug Administration in 2012. Its exact mechanism
of action was partly elucidated and it was early recognized that HHT (2) inhibited
protein synthesis at the level of the ribosome machinery. Interestingly, after a latency
period of two decades, the topic of Cephalotaxus alkaloids reemerged as a prolific
source of new natural structures. To date, more than 70 compounds have been
identified and characterized. Synthetic studies also regained attention during the
past two decades, and numerous methodologies were developed to access the first
semisynthetic HHT (2) of high purity suitable for clinical studies, and then high grade
enantiomerically pure CET (1), HHT (2), and analogs.
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