organic papers Acta Cryst. (2005). E61, o2515–o2517 doi:10.1107/S1600536805022002 Ravikumar et al.  C 23 H 27 FN 4 O 3 H 2 O 2 CH 4 O o2515 Acta Crystallographica Section E Structure Reports Online ISSN 1600-5368 Risperidone N-oxide hydrogen peroxide methanol solvate K. Ravikumar, a * B. Sridhar, a S. G. Manjunatha b and Saji Thomas b a Laboratory of X-ray Crystallography, Indian Institute of Chemical Technology, Hyderabad 500 007, India, and b Jubilant Organosys Ltd, Nanjangud, Mysore 571 302, India Correspondence e-mail: ravikumar_iict@yahoo.co.in Key indicators Single-crystal X-ray study T = 273 K Mean (C–C) = 0.003 A ˚ R factor = 0.054 wR factor = 0.156 Data-to-parameter ratio = 13.1 For details of how these key indicators were automatically derived from the article, see http://journals.iucr.org/e. # 2005 International Union of Crystallography Printed in Great Britain – all rights reserved In the crystal structure of the title compound {systematic name: 4-(6-fluoro-1,2-benzisoxazol-3-yl)-1-hydroxy-1-[2-(2- methyl-4-oxo-3,4,6,7,8,9-hexahydro-2H-pyrido[1,2-a]pyrimid- in-3-yl)ethyl]piperidine N-oxide hydrogen peroxide methanol solvate}, C 23 H 27 FN 4 O 3 H 2 O 2 CH 3 OH, the asymmetric unit contains one molecule of risperidone N-oxide, one methanol solvent molecule and one hydrogen peroxide molecule. The piperidine ring adopts a chair conformation, while the tetrahydropyridine ring has a sofa conformation. The hydrogen peroxide molecule links the risperidone molecules to form a chain. O—HO and C—HO interactions stabilize the crystal packing. Comment Risperidone is a relatively new antipsychotic agent, belonging to the chemical class of benzisoxazole derivatives, available worldwide since the early 1990s. The main pharmacological activities of risperidone include serotonin 5-HT2 receptor blockade and dopamine D2 antagonism (Megens, 1994). Recently, Ekins et al. (2002) generated a pharmacophore model, based on a three-dimensional quantitative structure activity relationship (three-dimensional QSAR) for the human Ether-a-go-go gene(hERG), with in vitro inhibition data for antipsychotic agents. Their model possessed four hydrophobes and one positive ionizable feature and showed a fit of the model to 9-hydroxyrisperidone, which illustrates an identical observed and predicted IC 50 . The presence of the positive ionizable domain in the model prompted us to study the structure of risperidone N-oxide. The crystal structure determination was undertaken to compare the structural features with that of risperidone itself and with other known serotonin and dopamine antagonists in the hope of obtaining a better insight into its structural features and activity. The conformation of risperidone N-oxide hydrogen peroxide methanol solvate, (I), and the atomic numbering scheme are given in Fig. 1. The asymmetric unit contains one Received 6 July 2005 Accepted 8 July 2005 Online 13 July 2005