The absolute configuration of (+)-oxopropaline D by theoretical calculation of specific rotation and asymmetric synthesis

The specific optical rotations of (R)-oxopropaline D calculated by two ab initio MO methods were +52+/-31degrees and +61+/-29degrees, respectively, and (+)-oxopropaline D (3) was presumed to have an R-configuration. On the basis of this theoretical result, the reaction of 1-litio-beta-carboline with (R)-glyceraldehyde acetonide followed by oxidation with MnO2 gave (R)-oxopropaline D acetonide (4a), which was consistent with the previously synthesized (+)-oxopropaline D acetonide (4) in all respects. From the results of theoretical calculations and the experimental synthesis, we determined that natural (+)-oxopropaline D (3) has an R-configuration.