Leigh DA, Pirvu L, Schaufelberger F. Stereoselective Synthesis of Molecular Square and Granny Knots.
J Am Chem Soc 2019;
141:6054-6059. [PMID:
30892025 PMCID:
PMC6492950 DOI:
10.1021/jacs.9b01819]
[Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
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We
report on the stereoselective synthesis of both molecular granny
and square knots through the use of lanthanide-complexed overhand
knots of specific handedness as three-crossing “entanglement
synthons”. The composite knots are assembled by combining two
entanglement synthons (of the same chirality for a granny knot; of
opposite handedness for a square knot) in three synthetic steps: first,
a CuAAC reaction joins together one end of each overhand knot. Ring-closing
olefin metathesis (RCM) then affords the closed-loop knot, locking
the topology. This allows the lanthanide ions necessary for stabilizing
the entangled conformation of the synthons to subsequently be removed.
The composite knots were characterized by 1H and 13C NMR spectroscopy and mass spectrometry and the chirality of the
knot stereoisomers compared by circular dichroism. The synthetic strategy
of combining building blocks of defined stereochemistry (here overhand
knots of Λ- or Δ-handed entanglement) is reminiscent of
the chiron approach of using minimalist chiral synthons in the stereoselective
synthesis of molecules with multiple asymmetric centers.
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