5′-Chlorospiro[1,3-dioxolane-2,3′-indolin]-2′-one: a potential anticonvulsant

The title compound, C10H8ClNO3, is a significant anticonvulsant agent. The indolinone system is essentially planar, the dihedral angle between the rings being 2.24 (8)°. The dioxolane ring adopts an envelope conformation; the dihedral angle between the plane through its four coplanar atoms and the indolinone system is 89.8 (1)°. The crystal structure is stabilized by a three-dimensional network of intermolecular N—H⋯O hydrogen bonds.

The title compound, C 10 H 8 ClNO 3 , is a significant anticonvulsant agent. The indolinone system is essentially planar, the dihedral angle between the rings being 2.24 (8) . The dioxolane ring adopts an envelope conformation; the dihedral angle between the plane through its four coplanar atoms and the indolinone system is 89.8 (1) . The crystal structure is stabilized by a three-dimensional network of intermolecular N-HÁ Á ÁO hydrogen bonds.
Data collection: AFC-4 Diffractometer Control Software (Rigaku, 1997); cell refinement: AFC-4 Diffractometer Control Software; data reduction: AFC-4 Diffractometer Control Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP (Johnson, 1965); software used to prepare material for publication: SHELXL97 and PARST (Nardelli, 1983  for potential drugs and their mechanism of action has been difficult because of their complexity. A series of spiro(1,3-dioxane-2,3'-indolin)-2'-one and structural analogues active against electrically and chemically induced seizures have been studied. These compounds contain both an oxoindole and a dioxolane moiety which have independently been seen in other anticonvulsants (Popp, 1977(Popp, , 1984. The basic model compound, mentioned above, was used to study the effects of various electron-donating, electron withdrawing and hydrophobic groups on the activity of the molecule. A bulky hydrophobic substituent at the 1'-position (oxoindole) generally tends to decrease the activity. The present compound, a chloro analogue was found to be most potent in the MES test. Since no common target site has yet been established, X-ray analysis was undertaken to search structural information which may help in the understanding of the mechanism of action at the molecular level.
The conformation of the title compound along with the atom-numbering scheme is shown in Fig 1. The carbonyl C atom to tetrahedral C atom distance is typical of a single bond. The C(2) -C(3) bond distance is slightly shorter but closely similar to the values found in other indoline nuclie (Itai et al., 1978;De & Kitagawa, 1991a,b;De, 1992). The lone pair of electrons on N(1) is involved in conjugation with the carbonyl group. This is also indicated by the slight lengthening of the C=O double bond [1.220 (4) Å] and the concomitant shortening of the two N -C(sp 2 ) single bonds [1.341 (4) Å and 1.412 (4) Å] (Codding et al., 1984). The least-squares planes through the five-and six-membered rings are inclined to one another at 2.24 (8) . The molecules are thus held together by a three-dimensional network of hydrogen bonds.

Experimental
The synthesis of the compound has been described earlier (Rajopadhye & Popp, 1988). Diffraction quality crystals were obtained by slow evaporation of an ethanol solution at room temperature.

Refinement
All the hydrogen atoms in the structure were located in a difference map except the two H-atoms on C10. They were placed at geometrically idealized positions. Geometric calculations were performed using SHELXL-97, PARST (Nardelli, 1983) programs.
supplementary materials sup-2 Figures   Fig. 1. ORTEP (Johnson, 1965) diagram of the Molecular structure with atom labels showing displacement ellipsoids at 50% probablity.   Refinement. Refinement on F 2 for ALL reflections except for 0 with very negative F 2 or flagged by the user for potential systematic errors. Weighted R-factors wR and all goodnesses 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 observed criterion of F 2 > 2sigma(F 2 ) is used only for calculating _R_factor_obs 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.