Parvistemins A-D, a new type of dimeric phenylethyl benzoquinones from Stemona parviflora Wright

Four naturally occurring dimeric phenylethyl benzoquinones, parvistemins A-D, were isolated from the aerial parts of Stemona parviflora Wright. Their constitutions were established by spectroscopic methods. Due to restricted rotation about the central biaryl axis, the compounds are chiral, although racemic. Their two respective atropo-enantiomers were resolved by HPLC on a chiral phase and were stereochemically characterized online, in hyphenation with circular dichroism (CD) spectroscopy (LC-CD coupling), combined with quantum chemical CD calculations.