Conformational study of cinchona and ephedra alkaloids

Chirality and Natun an closely associated. Living organisms use chiral catalysts (enzymes) to synthesize many of their chemical constituents. Over millions of years the complex compositions of enzymes have developed into efficient and specific catalysts for the synthesis (and breakdown) of chiral organic compounds. Because of the complexity of mynatic reactha, it is difficult to study the details of their reaction mechanisms directly from experiments. Recently several breakthroughs in the design and the synthesis of organic catalysts have taken place. With these catalysts it is possible to control the stereoselectivity of some reactions with efficiencies rivalling those of enzymes. In many casts th-e chiral organic catalysts am, like cnzymea, natclral products or their derivatives. However, such catalysts are much smaller than enzymes and are thus better suited to mechanistic studies. A recent example is given by lnouel . With the dipeptide cyclo-phcnyldaninc-histidinea s chiral caEatyst in a reaction between beaualdehyd