Cronin J R, Pizzarello S
Department of Chemistry and Biochemistry, Arizona State University, Tempe, AZ 85287-1604, USA.
Science. 1997 Feb 14;275(5302):951-5. doi: 10.1126/science.275.5302.951.
Gas chromatographic-mass spectral analyses of the four stereoisomers of 2-amino-2,3-dimethylpentanoic acid (dl-alpha-methylisoleucine and dl-alpha-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 alpha-methyl amino acids, isovaline and alpha-methylnorvaline, although the alpha hydrogen analogs of these amino acids, alpha-amino-n-butyric acid and norvaline, were found to be racemates. With the exception of alpha-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.
对从默奇森陨石中获得的2-氨基-2,3-二甲基戊酸的四种立体异构体（dl-α-甲基异亮氨酸和dl-α-甲基别异亮氨酸）进行气相色谱-质谱分析表明，在这两对对映体中，L-对映体均过量存在（分别为7.0%和9.1%）。对于另外两种α-甲基氨基酸——异缬氨酸和α-甲基正缬氨酸，也得到了类似结果，不过发现这些氨基酸的α-氢类似物——α-氨基正丁酸和正缬氨酸是外消旋体。除α-氨基正丁酸外，这些氨基酸在生物圈中要么未知，要么存在量有限。由于碳质球粒陨石形成于45亿年前，这些结果表明在生命起源之前，对有机化学演化存在不对称影响。
