5-Methoxy-1,2′,3-trimethyl-4,6-dioxa-2-azaspiro[bicyclo[3.2.0]hept-2-ene-7,4′-isoquinoline]-1′,3′(2′H,4′H)-dione

In the isoquinoline ring system of the title molecule, C16H16N2O5, the N-heterocyclic ring is in a half-boat conformation. The dioxaazaspiro ring is essentially planar [maximum deviation = 0.022 (1) Å] and forms a dihedral angle of 24.56 (4)° with the benzene ring.

In the isoquinoline ring system of the title molecule, C 16 H 16 N 2 O 5 , the N-heterocyclic ring is in a half-boat conformation. The dioxaazaspiro ring is essentially planar [maximum deviation = 0.022 (1) Å ] and forms a dihedral angle of 24.56 (4) with the benzene ring.  Huang et al. (2011). For the stability of the temperature controller used in the data collection, see : Cosier & Glazer (1986). For standard bond-length data, see: Allen et al. (1987). For ring conformations, see: Cremer & Pople (1975). For related structures, see: Fun et al. (2011a,b,c  Isoquinoline-1,3,4-trione derivatives have been reported to be a type of small molecular inhibitor against caspase-3 which can promote apoptosis of the cells (Du et al., 2008;Chen et al., 2006). Photoreactions of isoquinoline-1,3,4-trione could lead to structurally important motifs (Yu et al., 2010). Oxazole ring is found in some bioactive natural products such as Annuloline and Ostreogrycin A. Oxazoles can be used to inhibit the activity of malignant tumors (Harris et al., 2005). Since a lot of natural products especially the alkaloids containing isoquinoline or oxazole ring are bioactive, convenient method to construct such moieties is of current research interest (Zhang et al., 2004;Wang et al., 2010). The title compound which was derived from isoquinoline-1,3,4-trione and oxazoles (Huang et al., 2011) may has a potential use in biochemical and pharmaceutical fields. We report in this paper the crystal structure of the title compound with a relative configuration of (1S * , 4'S * , 5R * ).

Related literature
In the title racemic compound, Fig. 1, atoms C9, C10 and C12 are the stereo centers. The isoquinoline ring system (N1/C1-C9) is not completely planar, the N-heterocyclic ring (N1/C1-C3/C8/C9) being distorted towards a half-boat conformation with atom C9 deviating by 0.231 (1) Å from the mean plane through the remaining atoms, puckering parameters (Cremer & Pople, 1975 ith the benzene ring (C3-C8). Bond lengths (Allen et al., 1987) and angles are within normal ranges and comparable to related structures (Fun et al., 2011a,b,c). In the crystal of the title compound, unlike in our previously determined structures mentioned above, there are no significant intermolecular hydrogen bonds.

Refinement
All H atoms were positioned geometrically and refined using a riding model with C-H = 0.93 -0.96 Å and U iso (H) = 1.2 or 1.5 U eq (C). A rotating-group model was applied for the methyl groups. The highest residual electron density peak is located at 0.77 Å from C9 and the deepest hole is located at 0.52 Å from C2. Fig. 1. The molecular structure of the title compound showing 50% probability displacement ellipsoids for non-H atoms.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness 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 threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) 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.