X-Ray Crystal Analysis of Some Natural Products

The main part of the work described in this thesis is concerned with the determination of the structure of the alkaloid echitamine by an X-ray analysis of the methanol solvate of echitamine bromide. Two additional sections deal with the structure determination of acetylbromogeigerin ( a reduced azulene system), and of cedrelone iodoacetate (a triterpenoid). The work on the former was shared with Mr. A. T. McPhail and on the latter with Mr. I. J. Grant. As. far as possible alternate structure factor calculations and Fourier syntheses were carried out by each partner. A fourth section describes the analysis of a "supposed oxepin". In all of these structure determinations the heavy atom technique was used to overcome the phase problem. This consists of deriving approximate phases for the structure from the heavy atom and using them to calculate the electron density distribution. The method essentially converts the unmeasurable phase relationships into certain intensity relationships which can be measured directly. This technique is excellent for structure analysis of the type described in this thesis but is less suitable for the study of structural features of small molecules where accurate atomic positions are required. In the appendix various alternative methods of structure determination are described which were used in attempts to solve the structure of two hydrocarbons, dianthracene and circumanthracene. A note is also included on echitamine hydrobromide dihydrate for which considerable three-dimensional. data were collected and preliminary investigations carried out