LINEAR AND CYCLIC ALIPHATIC CARBOXAMIDES OF THE MURCHISON METEORITE -HYDROLYZABLE DERIVATIVES OF AMINO-ACIDS AND OTHER CARBOXYLIC-ACIDS

Analyses of fractionated aqueous extracts of the Murchison meteorite b y gas chromatography-mass spectrometry after silylation with N-methyl- N (tert-butyldimethylsilyl) trifluoroacetamide have revealed an extens ive series of linear and cyclic aliphatic amides. These include monoca rboxylic acid amides, dicarboxylic acid monoamides, hydroxy acid amide s, lactams, carboxy lactams, lactims, N-acetyl amino acids, and substi tuted hydantoins. Numerous isomers and homologues through at least C8 were observed in all cases, except for the N-acetyl amino acids and hy dantoins. Carboxy lactams, lactams, hydantoins, and N-acetyl amino aci ds are converted to amino acids by acid hydrolysis, thus, these compou nds qualitatively account for the earlier observation of acid-labile a mino acid precursors in meteoritic extracts. Laboratory studies of the spontaneous decomposition of N-carbamyl-alpha-amino acids and their d ehydration products, the 5-substituted hydantoins, have led to the rec ognition of a series of aqueous phase reactions by which amino acids a nd cyanic acid/cyanate ion in the primitive parent body might have giv en rise to several of the observed classes of amides, as well as to mo nocarboxylic acids, dicarboxylic acids, and hydroxy acids. A previousl y undescribed reaction of 5-substituted hydantoins with cyanic acid/cy anate ion to give carboxamides of the 5-substituent groups was observe d in the course of these studies. The presence of an extensive suite o f amides in a CM chondrite appears to be consistent with the interstel lar-parent body formation hypothesis for the organic compounds of thes e meteorites. The presence of carboxy lactams and lactams along with f ree amino acids suggests the possibility of further chemical evolution of meteorite amino acids by thermal polymerization. The cyclic amides , given their potential for hydrogen-bonded pair formation, might be c onsidered candidate bases for a primitive sequence coding system.