N-[2-(3-Methyl-1-oxo-1,2-dihydropyrrolo[1,2-a]pyrazin-2-yl)ethyl]methanesulfonamide

In the title compound, C11H15N3O3S, the dihedral angle between the five- and six-membered rings is 1.13 (18)°. The ethylmethanesulfonamide group is in a (+)synclinal conformation. In the crystal, intermolecular N—H⋯O and C—H⋯O hydrogen-bond interactions link molecules into zigzag ribbons parallel to the b axis. The ribbons are further connected by C—H⋯π interactions.

In the title compound, C 11 H 15 N 3 O 3 S, the dihedral angle between the five-and six-membered rings is 1.13 (18) . The ethylmethanesulfonamide group is in a (+)synclinal conformation. In the crystal, intermolecular N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen-bond interactions link molecules into zigzag ribbons parallel to the b axis. The ribbons are further connected by C-HÁ Á Á interactions.

Comment
Pyrrolopyrazinone compounds have been found to possess antitumor activity (Zöllinger et al., 2007), antifeedant effect on storage pests (Dubis et al., 1995) and to be potent and selective non-competitive mGluR5 antagonists (Micheli et al., 2008). Due to the interesting biological activities of pyrrolopyrazinone compounds, the title compound, which may have an improved analgesic activity (Wang et al., 2004), was synthesized and its crystal structure is reported here.
The bond lengths are in normal ranges (Allen et al., 1997). In the crystal structure ( Fig. 2), centrosymmetrically related molecules are linked by N-H···O hydrogen bonds (Table 1) into dimers forming fourteen-membered rings with R 2 2 (14) motifs (Bernstein et al., 1995). Adjacent dimers are linked by C-H···O hydrogen interactions into zigzag ribbons running parallel to the b axis. The crystal packing is further stabilized by inter-ribbon C-H···π interactions (Table 1; Cg1 is the centroid of the N2/C4-C7 ring).

Experimental
The title compound was prepared by reacting 2-(2-aminoethyl)-3-hydroxy-3-methyl-3,4-dihydropyrrolo[1,2-a]pyrazin-1(2H)-one (2.39 mmol) and methanesulfonyl chloride (4.76 mmol) in pyridine (2 ml) for 4 h. The reaction mixture was then poured into ice cold water and the solid obtained was filtered and washed thoroughly with water and then dissolved in aqueous NaHCO 3 solution. Filtration and then the acidification with dilute HCl gave the title compound as precipitate, which was then filtered and dried. Colourless block-shaped single crystals of the title compound suitable for X-ray structure determination were recrystalized from a dichloromethane/methanol solution (9.5:0.5 v/v) on slow evaporation of the solvent at room temperature after several days.

Refinement
The amide H atom was located in a difference Fourier map and refined isotropically. The remaining H atoms were placed in calculated positions with d(C-H) = 0.95 Å for aromatic, 0.99 for CH 2 and 0.98 Å for CH 3 atoms. The U iso values were constrained to be 1.5U eq of the carrier atom for methyl H atoms and 1.2U eq for the remaining H atoms. A rotating group model was used for the methyl groups. The highest residual electron density peak is located at 0.64 Å from C7 and the deepest hole is located at 0.74 Å from S1.
supplementary materials sup-2 Figures   Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atom-numbering scheme.  as those based on F, and R-factors based on ALL data will be even larger.