N-{N-2-(35-Difluoro­phenyl)acetyl-(S)-alanyl}-(S)-phenyl­glycine tert-butyl ester (DAPT): an inhibitor of γ-secretase revealing fine electronic and hydrogen-bonding features

摘要

The title compound, C23H26F2N2O4, is a dipeptidic inhibitor of γ-secretase, one of the enzymes involved in Alzheimer’s dis­ease. The mol­ecule adopts a compact conformation, without intra­molecular hydrogen bonds. In the crystal structure, one of the amide N atoms forms the only inter­molecular N—H⋯O hydrogen bond; the second amide N atom does not form hydrogen bonds. High-resolution synchrotron diffraction data permitted the unequivocal location and refinement without restraints of all H atoms, and the identification of the characteristic shift of the amide H atom engaged in the hydrogen bond from its ideal position, resulting in a more linear hydrogen bond. Significant residual densities for bonding electrons were revealed after the usual SHELXL refinement, and modeling of these features as additional inter­atomic scatterers (IAS) using the program PHENIX led to a significant decrease in the R factor from 0.0411 to 0.0325 and diminished the r.m.s. deviation level of noise in the final difference Fourier map from 0.063 to 0.037 e Å⁻³.