(1S*,4′S*,5R*)-1-Isopropyl-5-methoxy-2′,3-dimethyl-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, C18H20N2O5, the N-heterocyclic ring is in a half-boat conformation. The dioxa-2-azaspiro ring is essentially planar, with a maximum deviation of 0.029 (1) Å, and makes a dihedral angle of 30.63 (5)° with the benzene ring. The molecular structure is stabilized by a weak intramolecular C—H⋯O hydrogen bond, which generates a S(6) ring motif. In the crystal, molecules are linked via weak intermolecular C—H⋯O hydrogen bonds into a three-dimensional supramolecular network. Additional stabilization is provided by π–π stacking interactions between symmetry-related benzene rings with a centroid–centroid distance of 3.6507 (5) Å.

In the isoquinoline ring system of the title molecule, C 18 H 20 N 2 O 5 , the N-heterocyclic ring is in a half-boat conformation. The dioxa-2-azaspiro ring is essentially planar, with a maximum deviation of 0.029 (1) Å , and makes a dihedral angle of 30.63 (5) with the benzene ring. The molecular structure is stabilized by a weak intramolecular C-HÁ Á ÁO hydrogen bond, which generates a S(6) ring motif. In the crystal, molecules are linked via weak intermolecular C-HÁ Á ÁO hydrogen bonds into a three-dimensional supramolecular network. Additional stabilization is provided by stacking interactions between symmetry-related benzene rings with a centroid-centroid distance of 3.6507 (5) Å .

Comment
Isoquinolines are often found in bioactive natural products. They have been used to build blocks of benzo[c]phenanthridine alkaloids (Pollers-Wieers et al., 1981;Malamas et al., 1994;Yu et al., 2010). Isoquinoline-1,3,4-trione derivatives were 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). They can also attenuate apoptosis of neuronal cells induced by β-amyloid. .
Isoquinoline-1,3,4-trione and its derivatives have been reported to be redox mediators of photosystems and have been used as herbicides (Mitchell et al., 2000;. Oxazole rings are also 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 the isoquinoline or oxazole ring are bioactive, there has been intense development of methodology to construct such moieties (Wang et al., 2010). The title compound which was derived from isoquinoline-1,3,4-trione and oxazoles (Huang et al., 2011) may have potential use in biochemical and pharmaceutical fields. Due to the importance of the isoquinoline-1,3,4-trione derivatives, we report herein the crystal structure of the title compound with a relative configuration of (1S * , 4'S * , 5R * ).
supplementary materials sup-2 Refinement All H atoms were positioned geometrically and refined using a riding model with C-H = 0.93 or 0.98 Å and U iso (H) = 1.2 or 1.5 U eq (C). A rotating-group model was applied for the methyl groups. Fig. 1. The molecular structure of the title compound showing 50% probability displacement ellipsoids for non-H atoms. Intramolecular interaction is shown as dash line.

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.