Received 6 July 2006
The title compound, C14H17NO3, exhibits carboxylic acid group disorder about the C-CO2 axis, with site occupancies of 0.79 (5):0.21 (5). Molecules are linked by intermolecular O-HO=Ciso, C-HO=Ciso and C-H(arene) interactions (iso = isoindolinone).
The majority of structurally determined phthalimidine systems are either N-substituted or have a hydroxy substituent at the 3-position (McNab et al., 1997; Mukherjee et al., 2000). The title compound, (I), synthesized from L-leucine and ortho-phthalaldehyde (Allin et al., 1996), forms part of a structural study of phthalimidines (Brady et al., 1998; Gallagher et al., 2000; Gallagher & Brady, 2000; Gallagher & Murphy, 2001).
The molecular structure of (I) is depicted in Fig. 1 (S configuration) and selected dimensions are given in Table 1. The geometric data are normal (McNab et al., 1997) and in agreement with expected values (Allen, 2002). The five- and six-membered rings of the isoindole group are coplanar [dihedral angle between rings = 1.0 (2)°], and the isoindolinone atom O3 is 0.022 (5) Å from the C4N ring plane; this ring is oriented at 82.5 (5)° to the major orientation of the CCO2 plane (O1A/O2A/C1/C2).
Molecules of (I) exhibit CO2H group disorder about the C-CO2 axis with site occupancies of 0.79 (5):0.21 (5) for the major/minor sites, respectively. Conventional CO2H dimeric hydrogen bonding [R22(8) ring] is not present as a requirement of symmetry; rather, the primary hydrogen bonding as an (O-HO-H)n chain along  involving O1A/B-H1A/BO3i (Table 1) is described by a C(7) motif (Grell et al., 1999). The closest H atoms to the carbonyl O2A/B are at contact distances, e.g. H7O2Aiii is 2.71 Å, with C7-H7O2Aiii = 136° (symmetry codes iii as in Table 2). Disorder is facilitated on geometric grounds as O2 can rotate about the C1-C2 axis without greatly affecting the O1A/B-H1A/BO3i interaction distance (Fig. 2).
Combination of the O-HO=Ciso C(7) motif with a C(5) motif (from C10-H10AO3ii) generates a two-dimensional sheet comprising R43(20) rings as C(7)C(5)[R43(20)]; modest (arene)C-H(arene) interactions (Nishio, 2004) link these sheets (Fig. 3 and Table 2).
Compound (I) and the L-norvaline derivative, (II), C13H15NO3, (2S)-2-(1-oxo-1H-2,3-dihydroisoindol-2-yl)pentanoic acid (Gallagher & Brady, 2000), both crystallize in space group P212121 with similar cell dimensions. The corresponding atom coordinates and molecular conformations are comparable and hence the crystal structures are isomorphous. Molecules of (I) and (II) differ in their respective alkyl chains with the (CH3)2CHCH2- group in (I) occupying a similar volume as the disordered CH3CH2CH2- group in (II). The solid-state (KBr disk) C=O stretching vibrations are similar, 1736, 1638 cm-1 in (I) and 1730, 1649 cm-1 in (II), highlighting the analogous environments of both C=O groups in (I) and (II).
| || Figure 1 |
A view of (I), with the atomic numbering scheme; displacement ellipsoids are drawn at the 30% probability level. Both disorder components are shown.
| || Figure 2 |
Two molecules of (I), with atoms depicted as their van der Waals spheres, with C7 (C-HOiii contact) and C8 [C-H(arene)iii] labels.
| || Figure 3 |
A view of the C(7)C(5)[R43(20)] sheet in (I) with the unit-cell outline (symmetry codes as in Table 2); H atoms not involved in hydrogen bonding have been omitted for clarity.
The title compound (I) was prepared by the overnight reaction of L-leucine and o-phthalaldehyde in refluxing CH3CN under N2 (Allin et al., 1996). Filtration of the hot solution and subsequent slow cooling of the filtrate allowed the isolation of block-like colourless crystals. M.p. 485-487 K (uncorrected).
In the absence of significant anomalous dispersion effects, Friedel equivalents were merged prior to the final refinement cycles. The absolute configuration can be inferred from the known absolute configuration of the L-leucine starting material. H atoms were treated as riding atoms using the SHELXL97 (Sheldrick, 1997) defaults [at 294 (1) K], with C-H distances from 0.93 to 0.98 Å and O-H = 0.82 Å, and with Uiso(H) from 1.2 to 1.5 times Ueq(C,O).
Data collection: CAD-4 (Enraf-Nonius, 1992); cell refinement: SET4 and CELDIM (Enraf-Nonius, 1992); data reduction: DATRD2 in NRCVAX96 (Gabe et al., 1989); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: NRCVAX96 and SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Burnett & Johnson, 1996) and PLATON (Spek, 2003); software used to prepare material for publication: SHELXL97 and WORDPERFECT macro PREP8 (Ferguson, 1998).
JFG thanks Dublin City University, Forbairt (International Collaboration Grants) and the Royal Irish Academy for funding research visits to the University of Guelph, Canada, from 1995 to 1998. Professor George Ferguson is thanked for use of his diffractometer and computer system.
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