Methyl 1-{4-[(S)-2-(methoxycarbonyl)- pyrrolidin-1-yl]-3,6-dioxocyclohexa-1,4- dien-1-yl}pyrrolidine-2-carboxylate Simon J. Garden, a Janet M. S. Skakle, b Edward R. T. Tiekink c * and James L. Wardell d ‡ a Instituto de Quı ´mica, Departamento de Quimica Orga ˆnica, Universidade, Federal do Rio de Janeiro, Ilha do Funda ˜o, CT, Bloco A, Rio de Janeiro 21949-900, RJ, Brazil, b Department of Chemistry, University of Aberdeen, Old Aberdeen AB15 5NY, Scotland, c Department of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia, and d Centro de Desenvolvimento Tecnolo ´gico em Sau ´ de (CDTS), Fundac ¸a ˜o Oswaldo Cruz (FIOCRUZ), Casa Amarela, Campus de Manguinhos, Av. Brasil 4365, 21040-900 Rio de Janeiro, RJ, Brazil Correspondence e-mail: edward.tiekink@gmail.com Received 11 July 2010; accepted 13 July 2010 Key indicators: single-crystal X-ray study; T = 120 K; mean (C–C) = 0.003 A ˚ ; R factor = 0.038; wR factor = 0.136; data-to-parameter ratio = 9.4. The complete molecule of the title diproline ester quinone, C 18 H 22 N 2 O 6 , is generated by a crystallographic twofold axis, which passes through the centre of the benzene ring. Both –CO 2 Me groups are orientated to the same side of the benzene ring, with the carbonyl groups pointing roughly towards each other. The conformation of the proline residue is an envelope. In the crystal, a three-dimensional network is sustained by C—HO interactions involving both the quinone and carbonyl O atoms. Related literature For the oxidative nucleophilic addition of amines to quinones to form aminoquinones, see: Lyons & Thomson (1953). For background to mitomycin anticancer drugs, see: Tomasz (1995). For additional geometric analysis, see: Cremer & Pople (1975). Experimental Crystal data C 18 H 22 N 2 O 6 M r = 362.38 Monoclinic, C2 a = 11.4728 (5) A ˚ b = 7.1556 (4) A ˚ c = 11.7882 (7) A ˚  = 111.230 (3)  V = 902.07 (8) A ˚ 3 Z =2 Mo K radiation  = 0.10 mm 1 T = 120 K 0.24  0.12  0.08 mm Data collection Nonius KappaCCD area-detector diffractometer Absorption correction: multi-scan (SADABS; Sheldrick, 2007) T min = 0.896, T max = 1.000 6840 measured reflections 1114 independent reflections 1008 reflections with I >2(I) R int = 0.034 Refinement R[F 2 >2(F 2 )] = 0.038 wR(F 2 ) = 0.136 S = 1.23 1114 reflections 119 parameters 1 restraint H-atom parameters constrained  max = 0.64 e A ˚ 3  min = 0.63 e A ˚ 3 Table 1 Hydrogen-bond geometry (A ˚ ,  ). D—HA D—H HA DA D—HA C3—H3O2 i 0.95 2.56 3.400 (3) 147 C5—H5bO1 ii 0.99 2.54 3.407 (3) 146 C9—H9bO1 iii 0.98 2.38 3.186 (4) 139 Symmetry codes: (i) x þ 1 2 ; y  1 2 ; z; (ii) x þ 1 2 ; y  1 2 ; z; (iii) x þ 1 2 ; y þ 1 2 ; z þ 1. Data collection: COLLECT (Hooft, 1998); cell refinement: DENZO (Otwinowski & Minor, 1997) and COLLECT; data reduc- tion: DENZO and COLLECT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010). The use of the EPSRC X-ray crystallographic service at the University of Southampton, England, and the valuable assis- tance of the staff there is gratefully acknowledged. JLW acknowledges support from CAPES (Brazil), and SJG thanks CNPq and FAPERJ (Brazil) for financial support. Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: HB5550). References Brandenburg, K. (2006). DIAMOND. Crystal Impact GbR, Bonn, Germany. Cremer, D. & Pople, J. A. (1975). J. Am. Chem. Soc. 97, 1354–1358. Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565. Hooft, R. W. W. (1998). COLLECT. Nonius BV, Delft, The Netherlands. Lyons, J. M. & Thomson, R. H. (1953). J. Chem. Soc. pp. 2910–2915. Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276, Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M. Sweet, pp. 307–326. New York: Academic Press. Sheldrick, G. M. (2007). SADABS. Bruker AXS Inc., Madison, Wisconsin, USA. Sheldrick, G. M. (2008). Acta Cryst. A64, 112–122. Tomasz, M. (1995). Chem. Biol. 2, 575–579. Westrip, S. P. (2010). J. Appl. Cryst. 43, 920–925. organic compounds Acta Cryst. (2010). E66, o2071 doi:10.1107/S1600536810027947 Garden et al. o2071 Acta Crystallographica Section E Structure Reports Online ISSN 1600-5368 ‡ Additional correspondence author, e-mail: j.wardell@abdn.ac.uk.