42399-49-5 Enantiomer associations in the crystal structures of racemic and (2S,3R)-(-)-3-hydroxy-2-(4-methoxyphenyl)-2,3-dihydro-1,5-benzothiazepin-4(5H)- one

The crystal structures of racemic and (2S,3R)-(-)-3-hydroxy-2-(4-methoxyphenyl)-2,3-dihydro-1,5-benzothiazepin-4(5H)- one (C16H15NO3S) have been determined in order to compare the interactions between molecules of the same and opposite chirality. The enantiomeric associations observed in these two crystal structures are analysed, relating the differences to those found in the equivalent diastereomers, (2R, 3R) and/or (2S, 3S). Single-crystal X-ray diffraction data were collected at low temperature with Cu Kα radiation (λ = 1.54184 A). Optically active: monoclinic, space group C2, with a = 24.726(3), b = 5.2426(5), c =12.0726(12) A, β - 112.979(9)°, V = 1440.8(5) A3, Z = 4, Dx= 1.389 g cm-3, μ = 20.35 cm-1, the refinement on 2918 observed reflections gave R=0.0271. Racemic: monoclinic, space group P21/n, with a = 13.308(3), b = 4.8474(8), c = 22.130(4) A, β = 91.782(14), V= 1426.9(5) A3, Z=4, Dx= 1.403 g cm-3, μ= 20.54 cm-1, refined to R = 0.0318 for 2753 observed reflections. An intramolecular hydrogen bond between the hydroxy and carbonyl groups appears to stabilize the benzothiazepinone ring in the (P,2S,3R) boat conformation with the hydroxy and methoxyphenyl substituents in equatorial positions. In both crystal structures two N-H...O hydrogen bonds connect the molecules into dimers. In the optically active compound the two molecules are related by a twofold axis, in the racemate by an inversion centre. The racemate contains an additional hydrogen bond which is reflected by its higher melting enthalpy compared with the optically active compound. The difference in the chiral discrimination in the solutions of the cis-and trans-diastereomers does not appear to have its origin in the strong (O-H...O, N-H...O) hydrogen bonds, but rather in the weak (C-H...O) interactions. Acta Chemica Scandinavica 1996. https://www.lookchem.com/CASDataBase_42399-49-5.htm

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