Crystal structures of 2-[(4,6-diaminopyrimidin-2-yl)sulfanyl]-N-(naphthalen-1-yl)acetamide and 2-[(4,6-diaminopyrimidin-2-yl)sulfanyl]-N-(4-fluorophenyl)acetamide

The two title compounds are (diaminopyrimidin-2-yl)thioacetamide derivatives. In the first structure, the pyrimidine ring is inclined to the naphthalene ring system by 55.5 (1)°, while in the second, the pyrimidine ring is inclined to the benzene ring by 58.93 (8)°. In the crystals of both compounds, molecules are linked by pairs of N—H⋯N hydrogen bonds, forming inversion dimers with (8) ring motifs.

The title compounds, C 16 H 15 N 5 OS, (I), and C 12 H 12 FN 5 OS, (II), are [(diaminopyrimidine)sulfanyl]acetamide derivatives. In (I), the pyrimidine ring is inclined to the naphthalene ring system by 55.5 (1) , while in (II), the pyrimidine ring is inclined to the benzene ring by 58.93 (8) . In (II), there is an intramolecular N-HÁ Á ÁN hydrogen bond and a short C-HÁ Á ÁO contact. In the crystals of (I) and (II), molecules are linked by pairs of N-HÁ Á ÁN hydrogen bonds, forming inversion dimers with R 2 2 (8) ring motifs. In the crystal of (I), the dimers are linked by bifurcated N-HÁ Á Á(O,O) and C-HÁ Á ÁO hydrogen bonds, forming layers parallel to (100). In the crystal of (II), the dimers are linked by N-HÁ Á ÁO hydrogen bonds, also forming layers parallel to (100). The layers are linked by C-HÁ Á ÁF hydrogen bonds, forming a three-dimensional architecture.

Chemical context
As a result of the innate ability of bacteria to develop resistance to available antibiotics, there is a critical need to develop new agents to treat more strains that are resilient. Several classes of diaminopyrimidines have been reported as new therapeutic agents. Derivatives of diaminopyrimidines also exhibit anti-cancer activity (Xu et al., 2010), immune suppressant activity (Blumenkopf et al., 2002), hair-growthstimulant properties, anti-bacterial (Kandeel et al., 1994) and potential anti-microbial properties (Holla et al., 2006). They are also used as potential anti-AIDS agents (Nogueras et al., 1993) and anti-viral agents (Hocková et al., 2004). In this connection, the title 4,6-diaminopyrimidine-based analogues have been synthesized as potential antiviral agents against dengue for targeting NS2B/NS3 protease.

Structural commentary
The molecular structure of compound (I) is shown in Fig. 1. The pyrimidine ring is twisted with respect to the thioacetamide unit with the N1-C11-C12-S1 torsion angle being 140.88 (18) . The pyrimidine ring (C13-C16/N2/N3) makes a dihedral angle of 55.5 (1) with the naphthalene ring system (C1-C10). The amine nitrogen atoms, N4 and N5, deviate by 0.0235 and 0.0291 Å , respectively, from the plane of the pyrimidine ring.

Supramolecular features
In the crystal of compound (I), molecules are linked by pairs of N5-H5AÁ Á ÁN3 i hydrogen bonds, forming inversion dimers with an R 2 2 (8) ring motif (Table 1 and Fig. 3). The dimers are linked by bifurcated N-HÁ Á Á(O,O) and C-HÁ Á ÁO hydrogen bonds, forming layers parallel to the bc plane (Table 1 and Fig. 3).
In the crystal of compound (II), inversion dimers, with an R 2 2 (8), ring motif, are also formed via pairs of N5-H5AÁ Á ÁN2 i hydrogen bonds (Table 2 and Fig. 4). This time the dimers are linked by N-HÁ Á ÁO hydrogen bonds and also form layers parallel to the bc plane (Table 2 and Fig. 4). The layers are linked by C-HÁ Á ÁF hydrogen bonds, forming a threedimensional architecture (Table 2 and Fig. 4).

Synthesis and crystallization
Compound (I): To a solution of 4,6-diamino-pyrimidine-2thiol (0.5 g, 3.52 mmol) in 25 ml of ethanol, potassium hydroxide (0.2 g, 3.52 mmol) was added and the mixture refluxed for 30 min. Then 3.52 mmol of 2-chloro-N-(naphthalen-1-yl)acetamide was added and the mixture refluxed for 2.5 h. On completion of the reaction (monitored by TLC), the ethanol was evaporated in vacuo and cold water was added. The precipitate that formed was filtered and dried to give compound (I) as a crystalline powder (yield 92%). Compound (II): To a solution of 4,6-diamino-pyrimidine-2thiol (0.5 g, 3.52 mmol) in 25 ml of ethanol, potassium hydroxide (0.2 g, 3.52 mmol) was added and the mixture refluxed for 30 min. Then 3.52 mmol of 2-chloro-N-(4-fluorophenyl)acetamide was added and the mixture refluxed for 4 h. On completion of the reaction (monitored by TLC), ethanol was evaporated in vacuo and cold water was added and the precipitate formed was filtered and dried to give compound (II) as a crystalline powder (yield 88%).
Colourless block-like crystals were obtained by slow evaporation of a solution in CH 3 OH for compound (I) and C 4 H 8 O 2 for compound (II).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3 A view along the b axis, of the crystal packing of compound (I). Hydrogen bonds are shown as dashed lines (see Table 1). For clarity, only the NH and NH 2 hydrogens and the C-bound H atoms involved in hydrogen bonding have been included.