Bioactive polysaccharides from natural resources target various biological processes and are increasingly used as potential target molecules for drug development. However, the accessibility of branched and long complex polysaccharide active domains with well-defined structures remains a major challenge. Herein we describe an efficient first total synthesis of a highly branched heptadecasaccharide moiety of the native bioactive galectin-3-targeting polysaccharide from Carthamus tinctorius L. as well as shorter fragments of the heptadecasaccharide. The key feature of the approach is that a photo-assisted convergent [6+4+7] one-pot coupling strategy enables rapid assembly of the heptadecasaccharide, whereby a photoremovable o-nitrobenzyl protecting group is used to generate the corresponding acceptor for glycosylation in situ upon ultraviolet radiation. Biological activity tests suggest that the heptadecasaccharide can target galectin-3 and inhibit pancreatic cancer cell growth.
α-Xylosylated glycans and xylosyl
derivatives are biomedically
important molecules which show numerous bioactivities against infection,
cancer, inflammation, and so on. Lacking an efficient α-xylosylation
method, the synthesis of α-xyloside-containing molecules was
full of challenges. Herein, a robust method is presented for selective
α-xylosylation via combination of a rare conformation-controlled
strategy and the hydrogen-bond-mediated aglycone delivery method.
Various native branched α-xyloside structures necessitate an
orthogonally protected xyloside, and a three-pot preparation method
of the xylosyl donor was developed for this novel α-xylosylation
method, which was further applied in the first synthesis of the side
chain N of xyloglucan. This work provides an efficient α-xylosylation
method which would make various α-xyloside structures achievable.
The conformation-controlled strategy also has important reference
to the chemistry of five-carbon pyranose.
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