N-Acetyl-L-phenylalanyl-L-alaninamide

The conformation of the peptide chain in N-acetyl-L-phenylalanyl-L-alaninamide (NAFAA), C₁₄H₁₉N₃O₃, is rather extended and falls in the E region of the φ, ψ map, according to the classification of Zimmerman, Pottle, Némethy & Scheraga [Macromolecules (1977), 10, 1–9]. The values of φ, ψ torsion angles are like those of an anti­parallel β pleated sheet. Side-chain conformation of Phe residue is defined by χ₁ = −174.5 (4)° and χ₂ = 105.5 (6)° and comes within the B₂ class of the observed statistical distribution for the aromatic residues in peptides [Cody, Duax & Hauptman, (1973). Int. J. Peptide Protein Res. 5, 297–308]. Crystal packing is ruled by four intermolecular hydrogen bonds that involve all the donor groups, the acetyl O atom acting as a double acceptor. In the crystal there are ribbons of molecules translated along the a axis of the P2₁ space group and joined through three hydrogen bonds. The fourth hydrogen bond interconnects screw-related ribbons. The phenylalanyl rings stack parallel to the a direction with interplanar distances of 3.334 (7) Å.

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