We present the crystal and molecular structure of two key compounds of a new synthesis strategy for isomers of natural (2S,3R,4S)-4-hydroxyisoleucines, 2,3,5,6,7,8-hexa­hydro-3-(1-hydroxy-1-methyl-2-oxo­propyl)-6,8-methano-7,7,8a-tri­meth­yl-5H-1,4-benzoxazin-2-one, C₁₆H₂₃NO₄, and 2,3,5,6,7,8-hexa­hydro-3-(1-methyl-2-oxo­propyl)-6,8-methano-7,7,8a-tri­meth­yl-5H-1,4-benzoxazin-2-one, C₁₆H₂₃NO₃. A new optically pure chiral oxazinone auxiliary derived from (1R,2R,5R)-2-hydroxy­pinan-3-one was used.

The relative stereochemistry of methyl 6-oxo-5-(5-phenyl­tetrazol-2-yl)­piperidine-2-carboxyl­ate, C₁₄H₁₅N₅O₃, has been determined. It confirms the cis configuration of the piperidine ring as well as the position of the substituent on the tetrazole ring. The packing of the mol­ecules is influenced by N—HO and C—HN hydrogen bonds.

The heteroepitaxial Al_xGa₁-_xSb/GaSb (001) growth with different x aluminum content, from 0.05 to 0.2 prepared by Liquid Phase Epitaxy (LPE) is presented. The interest in this study is due to the layers of Al_xGa₁-_xSb systems should be well matched for fabrication of sources and detectors operating in the 1.3-1.6 micron range. The layered structure obtained was characterized mainly by high-resolution X-ray diffraction and reciprocal space mapping. In the case of x = 0.05 aluminum content, the relaxation is minimal, and almost without deviation respect to GaSb. As the aluminum content increases above 0.05, the relaxation is larger and deviation from GaSb substrate too. Crystallographic tilt is detected by a shift of layer diffraction maximum on reciprocal space maps. Deviation changes the intensity of layer respect to substrate peak in rocking curves and hence the estimation of thickness of layer obtained from them. A correction for estimated thickness of layers is obtained from mapping.

We present here the crystal structure of the title comp­ound, C₁₄H₁₉NO₄. It contains OH—O and NH—O hydrogen bonds, connecting the mol­ecules into centrosymmetric dimers and into infinite chains.

We present the crystal and molecular structures of 2,3,6,7,8,8a-hexa­hydro-6,8-methano-7,7,8a-tri­methyl-3-(1-methyl-2-oxo­propyl­idene)-5H-1,4-benzoxazin-2-one, C₁₆H₂₁NO₃, (III), and 2,3,6,7,8,8a-hexa­hydro-3-(2-hydroxy-1-methyl­propyl)-6,8-methano-7,7,8a-tri­methyl-5H-1,4-benzoxazin-2-one, C₁₆H₂₅NO₃, (V). These compounds are two of the four key intermediates in our synthetic route to (2R,3R,4R)-4-hydroxy­isoleucine. The two structures provide a full understanding of the stereochemistry in successive steps. This synthesis was based on a new optically pure chiral oxazinone auxiliary derived from (1R,2R,5R)-2-hydroxy­pinan-3-one.

We present the crystal and molecular structures of two new N-phthalyl-3-amino-2-arylpropionic acid pantolactonyl ester derivatives with 4-fluorophenyl and 3,4-dimethoxyphenyl as the aryl group, 2,3,4,5-tetrahydro-4,4-dimethyl-2-oxofuran-3-yl 3-phthalimido-2-(4-fluorophenyl)propanoate, C₂₃H₂₀FNO₆, and 2,3,4,5-tetrahydro-4,4-dimethyl-2-oxofuran-3-yl 3-phthalimido-2-(3,4-dimethoxyphenyl)propanoate ethyl acetate hemisolvate, C₂₅H₂₅NO₈·0.5C₄H₈O₂. This structural study confirms the S configuration of the C2 and validates the stereospecificity of our synthesis strategy.

There are two symmetry-independent formula units of the title compound, dimethyl 3-benzyl-2-(4-methyl-2,5-di­oxo­imid­azol­idin-1-yl)­butane­dioate, C₁₇H₂₀N₂O₆, per cell. The two symmetry-independent molecules differ in their configuration and are diastereomers. This structural study confirms a new side reaction during the synthesis of seven-membered cyclopeptides. The stereochemistry of both diastereomers has been established.

The silaproline-containing dipeptide N-(3,3-di­methyl-1-pivaloyl-1-aza-3-sila-5-cyclo­pentyl­carbonyl)-L-alanine iso­propyl­amide, C₁₇H₃₃N₃O₃Si, has two independent molecules in the asymmetric unit and each adopts a β-II folded conformation, where the amide on the terminal C interacts intramolecularly with the pivaloyl O atom. The five-membered silaproline ring is C^β-puckered, an infrequent conformation for the homol­ogous proline ring.

The crystal and molecular structure of 1-tert-butyl 4-ethyl (2′R,3′R,5′R,2S,3S)-3-bromo­methyl-3-hydroxy-2-[(2′-hydroxy-2′,6′,6′-tri­methyl­bi­cyclo­[3.1.1]­hept-3′-yl­idene)­amino]­succinate, C₂₁H₃₄BrNO₆, is presented. This compound is an intermediate in the new synthetic route to β-substituted β-hydroxy­aspartates, which are blockers of glutamate transport.