The absolute crystal structure of (−)-isolunine hydrobromide dihydrate at –150°C

Abstract

Crystals of (-)-isolunine hydrobromide dihydrate, C16H17NO4.2H20.HBr, are monoclinic, space group P21, with a = 11.1 l, b = 7.24, c = 22-33/~, fl= 101 ° 11' at 150°C, Z = 4, the asymmetric unit consisting of two molecules. Application of image-seeking procedures revealed the main components of the structure, while electron density and difference syntheses led to a complete solution of the molecular skeleton. Differentiation of the nitrogen and oxygen atoms in the skeleton was assisted by a mass spectroscopic determination of the molecular weight. Refinement was by least-squares and the absolute chirality was defined by Bijvoet's technique. The crystal structure involves a short approach distance, 2.45/~, between the lactam oxygen atom and a water molecule, the grouping being stabilized by the interpolation of a proton, H +. The relation of isolunine to lunine is outlined.