Enantiomeric Excesses in Meteoritic Amino Acids
John R. Cronin
and
Sandra Pizzarello
Gas chromatographic-mass spectral analyses of the four
stereoisomers of 2-amino-2,3-dimethylpentanoic acid
(DL-
-methylisoleucine and
DL--methylalloisoleucine) obtained from the Murchison
meteorite show that the L enantiomer occurs in excess (7.0 and 9.1%, respectively) in both of the enantiomeric pairs. Similar
results were obtained for two other -methyl amino acids, isovaline
and -methylnorvaline, although the hydrogen analogs of these
amino acids, -amino-n-butyric acid and norvaline, were
found to be racemates. With the exception of
-amino-n-butyric acid, these amino acids are either
unknown or of limited occurrence in the biosphere. Because carbonaceous chondrites formed 4.5 billion years ago, the results are indicative of
an asymmetric influence on organic chemical evolution before the origin
of life.
Department of Chemistry and Biochemistry, Arizona State
University, Tempe, AZ 85287-1604, USA.
