Methyl 2-acetamido-2-(4-hydroxy-2-methyl-1,3-dioxo-1,2,3,4-tetrahydroisoquinolin-4-yl)-4-methylpentanoate

In the isoquinoline ring system of the title molecule, C19H24N2O6, the N-heterocyclic ring is in a half-boat conformation. The molecular structure is stabilized by an intramolecular O—H⋯O hydrogen bond, which generates an S(7) ring motif. In the crystal, molecules are linked via intermolecular bifurcated N—H⋯(O,O) and weak C—H⋯O hydrogen bonds into a three-dimensional network.

In the isoquinoline ring system of the title molecule, C 19 H 24 N 2 O 6 , the N-heterocyclic ring is in a half-boat conformation. The molecular structure is stabilized by an intramolecular O-HÁ Á ÁO hydrogen bond, which generates an S(7) ring motif. In the crystal, molecules are linked via intermolecular bifurcated N-HÁ Á Á(O,O) and weak C-HÁ Á ÁO hydrogen bonds into a three-dimensional network.

Comment
Photocycloaddition of isoquinoline-1,3,4-trione combined with following transformation of the photocycloadducts has become facile method to build various scaffold containing an isoquinoline moiety (Yu et al., 2010;Huang et al., 2011). β-Hydroxy-amino acids are important building blocks to constitute more complex natural products. β-Hydroxy tyrosine and β-hydroxy phenylalanine derivatives are found in the clinically important antibiotic glycopeptides vancomycin, β-hydroxy leucine is found in (+)-lactacystin, and E-2-butenyl-4,N-dimethyl-l-threonine is an essential part of cyclosporine (Rao et al., 1995;Nagamitsu et al., 1996;Evans et al., 1986). α,α-Disubstituted amino acids represent a highly interesting class of non-proteinogenic amino acids, especially in view of their potential activity as enzyme inhibitors (Heimgartner, 1991;Rando, 1975). Many bioactive natural products contain β-hydroxy-amino acid or α,α-disubstituted amino acid and there has been intense interest to develop methodology to construct such moieties using photocycloadducts of oxazoles (Griesbeck et al., 2003;Zhang et al., 2004;Wang et al., 2010). The title compound was derived from photocycloadducts of isoquinoline-1,3,4-trione and oxazoles. Due to the importance of β-hydroxy-amino acid derivatives, we report in this paper the crystal structure of the title compound.

Experimental
The title compound was the main product from the acid-catalyzed transformation of the photocycloadducts of isoquinoline-1,3,4-trione and 4-isobutyl-5-methoxy-2-methyloxazole. The compound was purified by flash column chromatography with ethyl acetate/petroleum ether (1:5) as eluents. X-ray quality crystals of the title compound were obtained from slow evaporation of an acetone and petroleum ether solution (1:8) of the title compound, m.p. 425-427 K.

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.