Stereoselective Synthesis of C‑Glycosylated Pyrrolizidines through Nitrone Cycloadditions
Francisco Franco-Montalban, Mónica Díaz-Gavilán, Daniele Lo Re, Juan A. Tamayo
TL;DR
This paper presents a new method for creating complex sugar-like molecules with potential biological applications using a selective chemical reaction.
Contribution
A concise and stereoselective synthesis of C-glycosylated pyrrolizidines via nitrone cycloadditions is developed.
Findings
Five novel C-glycosylated pyrrolizidines were synthesized using 1,3-dipolar cycloadditions of nitrones with E-alkenes.
The reactions showed predictable anti-selectivity, leading to isoxazolidine intermediates.
Stereochemical assignments were confirmed using NOE analyses.
Abstract
Polyhydroxylated alkaloids, among which iminosugars represent a prominent subclass, are a structurally diverse family of carbohydrate mimics with significant biological activity. Herein, we report a concise and stereoselective synthesis of five novel C-glycosylated pyrrolizidines (15–19) related to casuarine and hyacinthacines, achieved through 1,3-dipolar cycloadditions of nitrones with E-alkenes. The reactions of nitrone 21 with fructose-derived α,β-unsaturated ester 20a and ketone 20b proceeded with predictable anti-selectivity, affording isoxazolidine intermediates that were transformed into pyrrolizidines via reductive N–O cleavage and subsequent ring closure. Careful stereochemical assignments were established by NOE analyses.
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Taxonomy
TopicsCarbohydrate Chemistry and Synthesis · Synthesis and Biological Activity · Asymmetric Synthesis and Catalysis