The absolute configuration of angular 3′-acyloxypyranocoumarins by vibrational circular dichroism exciton chirality

A complex mixture of lomatin C-3′ esters and (−)-O-angeloyllomatin 1 was isolated from the seeds of Prionosciadium thapsoides. Since a literature search revealed that some lomatin C-3′ monoesters have positive specific rotations, while others had negative values, the absolute configuration of all of the molecules was determined to be (R) by exciton chirality in the infrared region, and by chemical correlation. A single crystal X-ray study of acetyllomatin 3, using the Flack and Hooft parameters, independently confirmed this absolute configuration.

The absolute configuration of several lomatin C3′ monoesters was determined by exciton chirality in the infrared region, and confirmed by VCD DFT B3LYP/DGDZVP calculations of (R)-3′-acetyllomatin.Figure optionsDownload as PowerPoint slide

(R)-O-TigloyllomatinC19H20O5[α]D22 = +30.8 (c 0.11, CHCl3)Source of chirality: (+)-lomatinAbsolute configuration: (R)