ASYMMETRIC AUTOCATALYSIS AND AMPLIFICATION OF ENANTIOMERIC EXCESS OF A CHIRAL MOLECULE

THE homochirality of natural amino acids and sugars remains a puzzle f or theories of the chemical origin of life(1-18). In 1953 Frank(7) pro posed a reaction scheme by which a combination of autocatalysis and in hibition in a system of replicating chiral molecules can allow small r andom fluctuations in an initially racemic mixture to tip the balance to yield almost exclusively one enantiomer. Here we show experimentall y that autocatalysis in a chemical reaction can indeed enhance a small initial enantiomeric excess of a chiral molecule. When a 5-pyrimidyl alkanol with a small (2%) enantiomeric excess is treated with diisopro pylzinc and pyrimidine-5-carboxaldehyde, it undergoes an autocatalytic reaction to generate more of the alkanol. Because the reaction involv es a chiral catalyst generated from the initial alkanol, and because t he catalytic step is enantioselective, the enantiomeric excess of the product is enhanced, This process provides a mechanism by which a smal l initial imbalance in chirality can become overwhelming.