The principles underlying the use of powder diffraction data in solving pharmaceutical crystal structures.

Solving pharmaceutical crystal structures from powder diffraction data is discussed in terms of the methodologies that have been applied and the complexity of the structures that have been solved. The principles underlying these methodologies are summarized and representative examples of polymorph, solvate, salt and cocrystal structure solutions are provided, together with examples of some particularly challenging structure determinations.

N-(2-Carb-oxy-eth-yl)-2,5-dide-oxy-2,5-imino-d-mannonic acid [(3R,4R,5R)-1-(2-carb-oxy-eth-yl)-3,4-dihy-droxy-5-hy-droxy-methyl-l-proline].

The absolute stereochemistry of the title compound, C(9)H(15)NO(7), was determined from the use of d-glucuronolactone as the starting material. The compound crystallizes as the zwitterion. The five-membered ring adopts an envelope conformation with the -CH(2)OH-substituted C atom forming the flap. An intramolecular N-H⋯O hydrogen-bond occurs. In the crystal, the compound exists as a three-dimensional O-H⋯O intermolecular hydrogen-bonded network with each mol-ecule acting as a donor and acceptor for four hydrogen bonds.

N-Benzyl-3,5-dide-oxy-3,5-imino-1,2-O-isopropyl-idene-ß-l-lyxofuran-ose.

X-ray crystallography confirmed the formation, structure and relative stereochemistry of the title compound, C(15)H(19)NO(3), which contains a sterically congested four-membered azetidine ring system. The absolute configuration was determined by the use of l-arabinose as the starting material.