Details

Autor(en) / Beteiligte

• Stephens, P. J
• Pan, J. J
• Devlin, F. J
• Cheeseman, J. R

Titel

Determination of the Absolute Configurations of Natural Products Using TDDFT Optical Rotation Calculations: The Iridoid Oruwacin

Ist Teil von

• Journal of natural products (Washington, D.C.), 2008-02, Vol.71 (2), p.285-288

Ort / Verlag

Washington, DC: American Chemical Society and American Society of Pharmacognosy

Erscheinungsjahr

2008

Quelle

MEDLINE

Beschreibungen/Notizen

• We report the determination of the absolute configuration (AC) of the iridoid natural product oruwacin by comparison of the optical rotations, [α]D, of its two enantiomers, calculated using time-dependent density functional theory (TDDFT), to the experimental [α]D value, +193. Conformational analysis of oruwacin using density functional theory (DFT) identifies eight conformations which are significantly populated at room temperature. [α]D values of these eight conformations are calculated using TDDFT at the B3LYP/aug-cc-pVDZ//B3LYP/6–31G* level, leading to the conformationally averaged [α]D values of −193 for the (1R,5S,8S,9S,10S)-enantiomer and +193 for the (1S,5R,8R,9R,10R)-enantiomer. Comparison of the calculated [α]D values to the value of the natural product proves that naturally occurring oruwacin has the AC 1S,5R,8R,9R,10R. This AC is opposite to that assigned by Adesogan by comparison of the [α]D of oruwacin to that of the iridoid plumericin. Our results show that the assignment of the AC of a natural product by comparison of its [α]D to that of a chemically related molecule can be unreliable and should not be assumed to be definitive.