title: Enantiomer excesses of rare and common sugar derivatives in carbonaceous meteorites.
abstract: Biological polymers such as nucleic acids and proteins are constructed of only one-the d or l-of the two possible nonsuperimposable mirror images (enantiomers) of selected organic compounds. However, before the advent of life, it is generally assumed that chemical reactions produced 50:50 (racemic) mixtures of enantiomers, as evidenced by common abiotic laboratory syntheses. Carbonaceous meteorites contain clues to prebiotic chemistry because they preserve a record of some of the Solar System's earliest (∼4.5 Gy) chemical and physical processes. In multiple carbonaceous meteorites, we show that both rare and common sugar monoacids (aldonic acids) contain significant excesses of the d enantiomer, whereas other (comparable) sugar acids and sugar alcohols are racemic. Although the proposed origins of such excesses are still tentative, the findings imply that meteoritic compounds and/or the processes that operated on meteoritic precursors may have played an ancient role in the enantiomer composition of life's carbohydrate-related biopolymers.
authors.affiliation: Exobiology Branch, Space Science and Astrobiology Division, NASA Ames Research Center, Moffett Field, CA 94035; george.cooper@nasa.gov.
authors.forename: George
authors.initials: G
authors.lastname: Cooper
authors.affiliation: Exobiology Branch, Space Science and Astrobiology Division, NASA Ames Research Center, Moffett Field, CA 94035; NASA Postdoctoral Program, Universities Space Research Association, Columbia, MD 21046.
authors.forename: Andro C
authors.initials: AC
authors.lastname: Rios
mesh_terms: D002241:Carbohydrates / Q000737:chemistry*; D019110:Meteoroids; D013237:Stereoisomerism
chemical_list: D002241:Carbohydrates
keywords: aldonic acids; carbonaceous meteorites; enantiomer excesses; polyols; sugar acids