The title compound, C26H45N3O8, is a bicyclic molecule; the seven-membered diazepane ring has a twisted-chair conformation and the six-membered morpholine ring has a boat conformation.
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Acta Crystallogr C. 2010 April 15; 66(Pt 4): o174–o175. | PMCID: PMC2850304 |
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; Ge et al., 2007 , 2009 ; Peralta et al., 2005 ; Rey et al., 2007 ). In particular, it has been proposed that gadolinium(III) complexes of 6-amino-6-methylperhydro-1,4-diazepinetetraacetic acid (AAZTA) ligands are good candidates as MRI (magnetic resonance imaging) contrast agents due to their good thermodynamic stability, kinetic inertness and high relaxivity at neutral pH (Aime et al., 2004 ).
, 2009 ). The title compound, (I), was used as a precursor for one of the bifunctional ligands with a hydroxy arm and the complete synthesis and spectroscopic characterization of (I) was provided (Sengar et al., 2009 ). We report herein the molecular structure of compound (I) determined by X-ray crystallography (Fig. 1 ).). The maximum deviations were observed for the tert-butyl ester groups. As expected, compound (I) contains two rings, viz. a seven-membered 1,4-diazepane ring with a twisted-chair conformation and a six-membered morpholine ring which adopts a boat conformation (Fig. 1 ). For the seven-membered ring, the approximate plane can be defined by N4/C29/N5/C27, with atoms C30, C43 and C28 deviating above and below this plane. For the six-membered ring, atoms C44 and C46 occupy the prow and stern positions, respectively. The two rings are connected to each other via spiro atom C43 in a near orthogonal fashion; the dihedral angles for the N5/C30/C43/N6 and N4/C27/C43/C44 planes are –87.0 (2) and −71.9 (2)°, respectively [−85.6 (2) and –72.8 (2)°, respectively, for the other molecule in the unit cell].), as given in Table 1 . The puckering parameters for the seven-membered ring in (I) are different from the values for the AAZTA chelate (Table 1 ) or the protonated diazepane (daza-3HCl-3H2O) chelate (Romba et al., 2006 ). This shows that a large degree of flexibility is associated with the diazepane ring, which gives rise to the different puckering parameters for noncoordinated ligands. However, upon metal coordination, the diazepane ring adopts a pseudo-chair conformation and all three N atoms coordinate to the metal ion in a facial mode (Aime et al., 2008 ). | Table 1 Puckering parameters for (I) and the AAZTA chelate |
). Colorless crystals suitable for X-ray analysis were obtained by slow evaporation from a dichloromethane solution of (I) in air.
) T
min = 0.962, T
max = 0.980); cell refinement: SAINT-Plus (Bruker, 2003 ); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 ); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.