Conformational analysis of natural products

Pseudorotation of furanoses

The pseudorotation of furanoses, in particular ribofuranoses, is often described in terms of pseudorotation angles (P) and puckering (νmax). The endocyclic torsions (ν) can be approximated using the relationship derived by Altona and Sundaralingam [1].
νi=P*cos(νmax+(i-2)*4*π/5)
furanose
Using the torsions ν04 the torsions between the ring protons can be derived. Together with an appropriate Karplus equation[2] the corresponding coupling constants can be estimated, or experimental coupling constants can be used to determine the phase (P) and puckering (νmax) of the ring.

Literature

[1] C. Altona and M. Sundaralingam; J. Am. Chem. Soc. 94 (1972) 8205-8212.
[2] C.A.G. Haasnoot, F.A.A.M. DeLeeuw and C. Altona; Tetrahedron 36 (1980) 2783-2792.

Instructions

  1. Choose the correct substituents for positions C1'-C3' (or equivalent, e.g. C2,C3,C4 in fructofuranose).
  2. Choose the correct stereochemistry either by specifying the orientation of each substituent (check if below the plane of the ring) or select from ribo, arabino, &c below.
  3. Enter coupling constants if known.
Geometry
PositionSubstituentOrientation
Check for α(down)
C1'
C2'
C3'
Configuration
α-ribo β-ribo
α-arabino β-arabino
α-xylo β-xylo
α-lyxo β-lyxo
Coupling constants
3JH1',H2'
3JH2',H3'
3JH3',H4'