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The crystal and molecular structure and the absolute configuration of (—)-(S)-warfarin, C19H1604, have been determined by X-ray crystallographic techniques. Crystals of (—)-(S)-warfarin are orthorhombic, space group P212121, with a=10·883 (3), b=9·562 (3), and c=14·902 (5) Å. Solution of the structure was by direct methods, and refinement by least-squares calculations led to a conventional R of 0·053 (Mo Kα data). The molecule crystallizes as the intramolecular hemiketal and thus may be described as (2S,4S)-2,3H-2-methyl-4-phenyl-5-oxobenzopyrano[3,4-e]dihydropyran-2-ol. The absolute configuration was confirmed by recollecting with Cu Kα radiation a group of reflect ions predicted to have the greatest observable Bijvoet differences based on the anomalous scattering of oxygen and the parameters from the refinement with Mo Kα data. A group of 51 Friedel pairs, 86% of which indicate the S enantiomer, gave a 17% decrease in the residual over the R enantiomer. Refinement of the imaginary part of the anomalous dispersion of oxygen gave a value of 0·037 for Δf".


Pharmaceutical biotechnology; Pharmaceutical chemistry; Warfarin



Document Type

Journal Article