Determination of the absolute configuration of synthetic pterocarpans by chiral HPLC using on-line CD detection

Resolution of synthetic racemic pterocarpans was achieved by CD monitored HPLC using a chiral stationary phase. No sign of exciton coupling was seen in the CD spectra of the pterocarpan enantiomers. The predominance of the chromane chromophore was indicated by the high intensity of the (1) L(b) band. The chirality of both the chromane and dihydrobenzo[b]furane chromophores was found to be governed by the second chiral sphere. An oxygen atom in pseudoaxial position at the benzylic atom of the chroman ring system gave rise to an increased third-sphere contribution and the positive sign of the (1) L(b) and negative sign of the (1) L(a) band. This resulted in a general positive-negative-negative sign pattern of the (1) L(b), (1) L(a) and (1) B(b) bands of the second-eluted enantiomer of P helicity suggesting homochirality and the same absolute configuration of the chiral centers.