Absolute configuration determination of angular dihydrocoumarins from Peucedanum praeruptorum.

From Peucedanum praeruptorum, one new khellactone ester (3′ R )- O -acetyl-(4′ S )- O -angeloylkhellactone ( 3 ), as well as four known angular dihydropyranocoumarins ( 1 , 2 , 4 , 5 ) have been isolated. On the basis of NMR spectra and X-ray crystallography, their structures were determined. We have elucidated their absolute configuration by either chiral separation of their alkaline hydrolysis products with Rp-18 HPLC eluted with 5% hydroxypropyl-β-cyclodextrin (β-HCD) or by measurement of their CD spectra. A general rule relating the position and absolute stereochemistry of the khellactone esters to the sign of their Cotton effects in CD curves is proposed. [ABSTRACT FROM AUTHOR]