Enantiodivergent Synthesis of (R)- and (S)-Rolipram

Both enantiomers of rolipram (1) have been prepared in large quantity from a common intermediate rac-3-(3’-cyclopentyloxy-4’-methoxy)phenyl-4-nitro butyric acid (6), which was resolved by way of the two readily separable diastereoisomeric amides obtained with (S)-(-)-phenylethylamine. Reduction of the nitro group and intramolecular transamidation gave (R)-(-)-1 and (S)-(+)-1, respectively. CD spectra of both enantiomers of rolipram are reported and discussed. Both enantiomers of rolipram presented the same potency of inhibitory activity against recombinant cyclic-AMP-selective phosphodiesterase (PDE4) subtypes.