and warming under high vacuum afforded 26 9 g 43 of product as a mobile colorless oil other compounds of formula i may be prepared using the reaction techniques described in examples 1 through 5 using appropriate starting materials and reagents it is to be understood that all reaction conditions including choice of solvents reaction atmosphere reaction temperature duration of the experiment and workup procedures are chosen to be conditions standard for that reaction which should be readily recognized by one skilled in the art it is understood by one skilled in the art of organic synthesis that the functionality present on portions of the educt molecule must be compatible with the reagents and reactions starting materials reagents and solvents used in the synthesis of the contrast agents can be obtained from chemical suppliers such as aldrich baker and eastman chemical companies or they may be prepared by techniques known in the prior art the natural pharmaceutically acceptable clays incorporated in the present invention comprise aluminum silicates they are used in purified form suitable for administration to patients the natural pharmaceutically acceptable clays of the present invention generally referred to as smectities consist of dioctohedral smectites and trioctahedral smectites the clays are available from chemical suppliers.