2-Ethyl-3-[(R)-2-phenylbutanamido]quinazolin-4(3H)-one monohydrate

In the title compound, C20H21N3O2·H2O (EQR·H2O), the quinazoline ring system forms dihedral angles of 53.1 (1) and 85.6 (1)° with the phenyl ring and the amide link, respectively. In the crystal, O—H⋯O hydrogen bonds link two EQR and two water molecules into a centrosymmetric R 4 4(18) ring motif. N—H⋯O hydrogen bonds further link these hydrogen-bonded fragments into columns extending in [010].

In the title compound, C 20 H 21 N 3 O 2 ÁH 2 O (EQRÁH 2 O), the quinazoline ring system forms dihedral angles of 53.1 (1) and 85.6 (1) with the phenyl ring and the amide link, respectively. In the crystal, O-HÁ Á ÁO hydrogen bonds link two EQR and two water molecules into a centrosymmetric R 4 4 (18) ring motif. N-HÁ Á ÁO hydrogen bonds further link these hydrogenbonded fragments into columns extending in [010].
In the title compound, EQR.H 2 O ( Fig. 1), all bond lengths and angles are normal and correspond well to those observed in the related structures (Smith et al., 2004;Yang et al., 2009;Srinivasan et al., 2011). The quinazoline ring system forms a dihedral angle of 53.1 (1)° with the phenyl ring and an angle of 85.6 (1)° with the amide link. A pair of EQR molecules accepts O-H···O hydrogen bonds from two water molecules to form a R 4 4 (18) ring motif. These rings are linked by N-H···O bonds to form columns parallel to the b-axis (Fig. 2).
101-103 °C. The title compound (I) appears from its NMR spectra as a mixture of two diastereoisomers in unequal proportions (Ia:Ib = ca. 4:6), due to restricted rotation around the N-N axis (Smith et al., 2004), but the X-ray crystallography showed a single type of crystal containing just one diastereoisomer but with both enantiomers in equal proportions (the structure displayed shows the structure as 2-ethyl-3-((R)-2-phenylbutanoylamino)-3H-quinazolin-4-one hydrate). The 1 H NMR spectrum also showed diastereotopism for the CH 2 protons of the ethyl groups, but was CH 2 CH of Ib), 26.6 (t, CH 2 Ar of Ib), 25.9 (t, CH 2 Ar of Ia), 12.6 (q, CH 3 CH 2 CH of Ia), 12.5 (q, CH 3 CH 2 CH of Ib), 11.0 (q, CH 3 CH 2 Ar of Ia), 10.8 (q, CH 3 CH 2 Ar of Ib).

Refinement
The hydrogen atoms of the water molecule were located in the difference Fourier map and refined isotropically. The Cand N-bound hydrogen atoms were positioned geometrically, and refined using a riding model, with U iso (H) = 1.2-1.5 U eq of the parent atom.

Figure 1
The molecular structure of the title compound showing the atomic numbering and 50% probability displacement ellipsoids for non-H atoms.