Preparative Separation and Characterization of the four Stereoisomers of an Indane Carboxylic Acid Derivative of Lapachol

Preparative separation and characterization of an indane carboxylic acid diastereomer 3 from chemical transformation of lapachol 1 and the enantiomeric resolution of each one of the former compounds by chiral HPLC, plus the comparison between the experimental and calculated CD spectra, by spectroscopic and quantum chemical calculation of their circular dichroism (CD) spectra is described. The use of simple and correct cis-trans nomenclature, based on the relative direction (above or below the ring plane) of the two priority substituents, namely the hydroxy and prenyl groups explains clearly the formation of the diastereomers in different proportions. The cis-isomer 3b was presumed to be the major diastereomer on the basis of steric factors (interaction with methyl ester) and later on, this assumption was experimentally confirmed (CD experimental-calculated comparison) and attributed (RS/SR) absolute configuration. The diastereoisomer 3a was attributed (RR/SS) or trans-isomer. The formation of compound 3 from Lapachol involves benzilic acid rearrangement reaction.