Capecitabine from X-ray powder synchrotron data. Corrigendum

Erratum to Acta Cryst. (2009), E65, o1325–o1326.

Abstract

In the paper by Rohlicek et al. [Acta Cryst. (2009), E65, o1325–o1326], one H atom was placed incorrectly.

Following our powder-diffraction study of capecitabine (Rohlicek et al., 2009 ▸), Malińska et al. (2014 ▸) published the crystal structure of the same mol­ecule based on single-crystal data. Although they modelled the wrong enanti­omer [as was pointed out by Kratochvil et al. (2016 ▸)], the structures are very similar after inverting the single-crystal structure, including the disordered part of the mol­ecule (Fig. 1 ▸). Since single-crystal diffraction is more sensitive to H atoms than powder diffraction, Malinska et al. (2014 ▸) were able to locate the H atoms directly. This indicated a different tautomeric form of capecitabine to that assumed in our study, and as they pointed out, we had therefore placed one H atom wrongly.

Figure 1.

Overlay of the capecitabine mol­ecular structures arising from powder diffraction (blue) and from single-crystal diffraction data (red). Only non-H atoms are shown for clarity.

In our defence, in the powder study, we placed the H atoms geometrically according to a reasonable chemical structure for capecitabine, which shows the tautomeric H atom attached to the N atom of the carbamate group and the plausible formation of an inter­molecular N—H⋯O hydrogen bond. As shown by Malińska et al. (2014 ▸), the H atom is actually located on the N atom of the pyrimidine ring (Fig. 2 ▸), thereby forming an intra­molecular N—H⋯O link.

Figure 2.

Schemes for the tautomeric forms of capecitabine (a) assumed in the powder-diffraction study and (b) established in the single-crystal study of Malinska et al. (2014 ▸).

With respect to the fact that structure solution from powder diffraction data is based on the proposed molecular structure, readers should beware of the incorrectly placed H atom in Rohlicek et al. (2009 ▸) and they should be also beware of the wrong enantiomer in a single-crystal study of Malińska et al. (2014 ▸).