With glycosyl o-alkynylbenzotes as donors, a highly efficient protocol to construct the challenging glycosidic linkages at C3-OH of C23-oxo oleanane triterpenoids is disclosed, on the basis of which different strategies for the highly efficient synthesis of QS-21 analogues with the west-wing trisaccharide of QS-21 have been established.
Recent achievements in triterpenoid semi-synthesis have been accounted, which were divided into three parts according to the applied strategies, including functionalization strategy, C-skeleton modification strategy, and glycosylation strategy. In the functionalization strategy part, both functional group inter-conversions and new functional group installations on triterpenoid starting materials were included. As for the C-skeleton modification strategy section, the contents were further divided into three parts according to the applied tactics, including C-skeleton rearrangement, ring scission, and extra heterocyclic ring introduction tactics. Meanwhile, in the glycosylation strategy section, conspicuous achievements in semi-synthesis of both natural and artificial triterpene saponins were encompassed. In the whole account, the pivotal transformations that brought about striking chemical structure variations on the triterpenoid starting materials were highlighted, which would provide inspiration to investigators who have been engaged in or are going to enter this area.
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