Crystal structure of diethyl [(4-nitrophenylamino)(2-hydroxyphenyl)methyl]phosphonate methanol monosolvate

In the title compound, C17H21N2O6P·CH3OH, the planes of the 4-nitroaniline and 2-hydroxyphenyl groups form a dihedral angle of 84.04 (8)°. The P atom exhibits tetrahedral geometry involving two O-ethyl groups, a Cα atom and a double-bonded O atom. In the crystal, O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds link the α-aminophosphonic acid and methanol molecules into chains that propagate parallel to the a axis.


S1. Introduction
As mimics of natural amino acids, α-aminophosphonic acids and related derivatives are currently attracting a great deal of interest in medicinal chemistry due to their important biological effects (Arizpe, et al., 2011). They have been reported to possess a wide range of biological functions. These include antibacterial activities (Allen et al., 1978), action as inhibitors of enzymes such as rennin, HIV proteases, serine proteases and so on (Sieńczyk, et al., 2009).

S2.1. Synthesis and crystallization
The synthesis of o-cresol α-aminophosphonate N-derivatives with rigid structures was achieved through the Pudovik reaction reaction (Cherkasov et al., 1998). We obtained the title compound following our earlier report (Wang et al., 2012). The synthesis involved two steps: a) the Schiff bases were first prepared in a condensation of 4-nitroaniline and salicylaldehyde in methanol solvent by refluxing equimolar amounts of reagents; b ) reaction of Schiff base with a diethyl phosphonate in methanol solvent under reflux. The title compound was obtained from the filtrate after three days.

S2.2. Refinement
The amine H atom was located in a difference Fourier map and refined freely. All other H atoms were placed in

Figure 1
A view of the structure of the title compound with displacement ellipsoids drawn at the 30% probability level.

Figure 2
Crystal packing of the title compound, drawn so as to highlight the hydrogen-bonding interactions between molecules.

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.