The second most abundant amino acid was alanine (1.7 ppm) with a relative enrichment of L-alanine (Table 1). Such a distribution difference shows the heterogeneity of amino acids in the meteorite. Glycine was the most abundant amino acid (~3 ppm in total), consistent with previous studies 6, 11, even though α-aminoisobutyric acid (AIBA) or isovaline is sometimes the most abundant in the Murchison meteorite e.g. Many other amino acids (especially for C 5-C 7 amino acids) were reported from the Murchison meteorite 5, 11, but could not be detected in this study due to the lack of appropriate standards. Thirty amino acids between C 2 and C 6 were identified in the hydrolyzed samples of the water extract and the extract residue of the Murchison meteorite (see the Supplementary Information, SI, for the detailed analytical methods and quantification) without consideration of their enantiomers (Table 1). Newly discovered amino acids in Murchison These new findings will expand our knowledge concerning the formation mechanism of meteoritic amino acids. However, comprehensive formation mechanisms of extraterrestrial amino acids are not well understood.Įven though the Murchison meteorite has been studied for the occurrence of amino acids for almost 50 years, this study has revealed the presence of ten new amino acids, including a new family of nine hydroxy C 3 and C 4 amino acids. It has been proposed that β-alanine could be formed by Michael addition of NH 3 to cyanoacetylene 10 and that γ- and δ-amino acids could be formed by hydrolysis of 5-membered and 6-membered lactams, respectively 9. bearing amino and carboxyl group at the same carbon), and cannot explain the formation of other amino acids (β, γ and δ structures). However, the Strecker reaction produces only α-amino acids (i.e. It is generally considered that meteoritic amino acids could be formed in the meteorite parent bodies by the Strecker reaction, in which aldehyde or ketone reacts with cyanide and ammonia followed by hydrolysis to produce α-amino acid 9. The hydrolyzed amino acids are present as their precursors and the molecular occurrence of precursors relates to the sources and formation pathways of extraterrestrial amino acids 7, 8. The concentration and structural diversity of amino acids generally increase after hydrolysis of the water extract of the CM chondrites 6, even though some CR chondrites yielded more free amino acids than hydrolyzed amino acids 5. Although the presence of C 10 amino acids has been suggested 5, definitive C 10 amino acid identification was not assigned to the molecular structure due to lack of the appropriate standards. Currently, a total of 86 amino acids have been identified in the Murchison meteorite as α, β, γ and δ amino structures with a carbon number between C 2 and C 9 including dicarboxyl and diamino functional groups 2, 3, 4. The Murchison meteorite is classified as a CM2 (Mighei-type) chondrite, moderately altered by aqueous activity on the parent body (e.g. The extraterrestrial amino acid distribution has been extensively examined using carbonaceous chondrites, which are the most chemically primitive meteorites containing volatile components such as water and organic matter, particularly the Murchison meteorite since it’s fall in 1969. The extraterrestrial synthesis of amino acids is an intriguing discussion concerning the chemical evolution for the origins of life in the universe, because amino acids are fundamental building blocks of terrestrial life.
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