rac-Dimethyl [(9-anthryl)(4-methylanilino)methyl]phosphonate

The title compound, C24H24NO3P, crystallizes as a racemate with two molecules in the asymmetric unit. The structural features (bond lengths and angles) of the two molecules are almost identical. The dihedral angle between the anthracene and toluidine rings is similar in the two molecules, with values of 48.36 (9) and 51.15 (9)°. The methyl groups of one of the methoxy groups in one molecule is disordered over two sets of sites, the major component having a site occupancy of 0.636 (3). In the crystal, both molecules are linked into inversion dimers by pairs of N—H⋯O hydrogen bonds.

The title compound, C 24 H 24 NO 3 P, crystallizes as a racemate with two molecules in the asymmetric unit. The structural features (bond lengths and angles) of the two molecules are almost identical. The dihedral angle between the anthracene and toluidine rings is similar in the two molecules, with values of 48.36 (9) and 51.15 (9) . The methyl groups of one of the methoxy groups in one molecule is disordered over two sets of sites, the major component having a site occupancy of 0.636 (3). In the crystal, both molecules are linked into inversion dimers by pairs of N-HÁ Á ÁO hydrogen bonds.
Data collection: CAD-4 EXPRESS (Enraf-Nonius, 1994); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999 Comment α-Aminophosphonic acid derivatives have gained widespread interest because of their versatile biological activity, that affords much opportunities of these compounds for pharmaceutical applications (Cherkasov & Galkin, 1998). They are considered to be bioisosteric phosphorus analogues of natural α-aminocarboxylic acids, in which the planar carboxylic acid group is replaced by a bulky phosphonic acid moiety (Orsini et al., 2010). Due to the tetrahedral configuration at phosphorus, aminophosphonates serve as stable analogues of the unstable tetrahedral carbon intermediates formed in enzymatic processes and therefore act as enzyme inhibitors Rassukana et al. (2009). Numerous aminophosphonate derivatives are used as haptens for catalytic antibodies, metabolic regulators, antibiotics, as well as therapeutics, including antihypertensive, antibacterial, antiviral and antitumor agents. The title compound has been synthesised and tested for cytotoxicity on Balb/c 3 T3 (clone 31) cells, for in vitro antitumor activity using a panel of six human epithelial cancer cell lines and for genotoxicity and antiproliferative activity in vivo Kraicheva et al. (2011). Here we report its crystal structure.
It crystallizes with two independent molecules in the assymetric unit. The anthracen and toluidine moieties are nearly planar (with respective r.m.s. of 0.076/0.008 and 0.065/0.009 Å for molecule A and B). The interplanar angle beteween the anthracen and the toluidine is 48.36 (9) and 51.15 (9)°, respectively. In the crystal structure of the studied compound symmetrically equivalent molecules of opposite chirality-enantiomers are connected by centrosymmetric N-H···O hydrogen bonds into dimmers (Fig. 2). One of the four methyl groups (form the two dimethyl phosphonate fragments) is disordered over two positions. The positional disorder on the C methyl atom was resolved by finding alternative positions from the difference Fourier map, and was subsequently refined. The occupancy of the major component of the methyl group is 0.636 (3).

Experimental
The studied compound was obtained according to Kraicheva et al. 2011. Suitable crystals were grown by slow evaporation from methanol/methylene chloride solution mixture (1:1 v/v) at room temperature.

Refinement
All H atoms bonded to C or N were placed in idealised positions (C-H aromatic = 0.93 Å, C-H methine = 0.98 Å, C-H methyl = 0.96 Å and N-H = 0.86 Å. All H atoms were constrained to ride on their parent atoms, with U iso (H) = 1.2U eq (C or N) and 1.5U eq (C methyl ).