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1 Supporting Information Cooper et al /pnas SI Text Subsequent Chemistry of Keto Acids/Amides/Nitriles (Fig. 2A). The presence of a carbonyl (ketone) group in the keto acids may have lead to the synthesis of other known meteoritic compounds: ketones and aldehydes react readily with the strong nucleophile CN to give cyanohydrins and (after hydrolysis) hydroxy and amino carboxylic acids (e.g., Fig. 2). The formation of dicarboxylic acids from the keto acids should proceed readily due to the relative ease of cyanohydrin formation at a ph range ( 6 11) relevant to the meteorite parent-body: pyruvic acid and oxaloacetic acid form cyanohydrins in a matter of minutes when mixed with KCN at alkaline ph (1). In the course of this work we have seen the formation of the corresponding dicarboxylic acids from pyruvate, acetoacetate, and levulinate, respectively, after addition of CN although the neutral cyano or amide forms (Fig. 2A) of each acid may give higher yields. There is evidence of the production of meteoritic amino and imino acids by CN addition to aldehydes and ketones (2). Cyanohydrin formation is catalyzed by metal cyanides: such cyanides are also found in interstellar space (3). The reactions outlined in Fig. 2A are consistent with some observations of meteorite organic compounds. We tentatively identified compounds that are likely to be unsaturated (contain a double bond) keto acids of 5C through eight-carbon (8C) their mass spectra are similar to the corresponding saturated compounds in Fig. 1. A set of reactions by these and other keto acids may also help to answer unsettled questions (6) about the origins of non-α amino and hydroxy acids (i.e., compounds containing an amino or hydroxy group on a carbon not adjacent to the carboxyl carbon) and branched amino and hydroxy acids (e.g., Fig. 2A) in meteorites. The Strecker reaction, thought to have formed at least a portion of meteoritic α-amino and α-hydroxy acids, does not produce non-α acids; and branched amino and hydroxy acids including α-alkyl dicarboxylic acids in meteorites may have formed by a different (and unknown) mechanism than nonbranched (6). The reactions in Fig. 2A may be a partial solution to such questions. In our Strecker experiments branched hydroxy dicarboxylic acids have been synthesized from some of the present keto acids as in Fig. 2 A and B. These are the simple (and expected) α-methyl acids the methyl group being the same as the terminal methyl group of the starting keto acids. However if meteoritic monoacids with the keto group at other positions were present then dicarboxylic acids with other α-alkyl groups would result. In the case of the final meteoritic keto monoacids (Fig. 1), branched members would have resulted if the starting nitriles were not all straight-chained or if ketene inserted into internal carbon bonds (of course, Strecker reactions could also transform these monoacids into dicarboxylic acids). Conditions Related to Those of the Carbonaceous Meteorite Parent Bodies. ph: extracts of carbonaceous meteorites are often in the ph 7 9 range, partly due to the abundance of carbonates: Murchison contains 1% calcium carbonate alone (4). Temperature: Most estimates of aqueous alteration temperatures for carbonaceous meteorites are in the range of 0 to 25 C (7). HCN content: HCN is ubiquitous and abundant in comets: one estimate of the total abundance of HCN, before polymerization, is 4% relative to water (5). An oxidant, hydrogen peroxide, was also included is some of the experiments: carbonaceous meteorites show various degrees of oxidation (7) and a relatively mild oxidant such as hydrogen peroxide is also effective at converting nitriles (produced from KCN and keto acids) to carboxamides and carboxylic acids. 1. Green DE, Williamson S (1937) Pyruvic and oxaloacetic cyanohydrins. Biochem J 31: Lerner NR, Cooper GW (2005) Iminodicarboxylic acids in the Murchison meteorite: evidence of Strecker reactions. Geochim Cosmochim Acta 69: Pulliam RL, et al. (2010) Identification of KCN in IRC þ 10;216: evidence for Selective Cyanide Chemistry. ApJL 725:L181 L Clayton RN, Mayeda TK (1984) The oxygen isotope record in Murchison and other carbonaceous chondrites. Earth and Planet Sci Lett 67: Rettig TW, Tegler SC, Pasto DJ, Mumma MJ (1992) Comet outbursts and polymers of HCN. Astrophys J 398: Pizzarello S, Cooper GW, Flynn GJ (2006) Meteorites and the Early Solar System II, eds Lauretta DS, McSween HY (Univ Arizona Press, Tucson), Brearley AJ (2006) Meteorites and the Early Solar System II, eds Lauretta DS, McSween HY (Univ Arizona Press, Tucson), of5

2 Fig. S1. Gas chromatography-mass spectrometry (GC-MS) analysis of newly identified meteoritic compounds. (A) Chromatograms of each compound class. The hydroxy tricarboxylic acids, levulinic acid, and pyruvic acid (inset) and tricarboxylic acids are tert-butyldimethylsilyl (tbdms) derivatives. The remaining keto acids are trimethylsilyl (TMS) derivatives. Letter labels in the keto acid chromatogram: a, 3-methy-4-oxopentanoic acid (6C); b, 7C unsaturated keto acid; c, 6C isomer, d, 8C unsaturated keto acid; and e, 7C isomer. (B) Mass spectra of standards and the corresponding meteoritic compounds. Pyruvate (and acetoacetate) form di-tbdms derivatives due to keto-enol tautomerism. Coelution of another compound is evident in the spectrum of pyruvic acid. tbdms derivatives generally give reliable molecular weight (M) information, i.e., the M þ -57 ion. For example, M for pyruvate di-tbdms is 316 amu therefore M þ -57 is 259. For α-ketoglutaric acid (not shown) significant fragments include 473, 431, 403, and 375 amu: likely corresponding to M þ -CH 3,M þ -57, M þ -57-CO, and M þ -57-CO-CO respectively. 2of5

3 Fig. S2. Gas chromatography-isotope ratio mass spectrometry of levulinic acid-tms after purification by ion chromatography. The same chromatography conditions were used for 13 C 12 C and D/H measurements. Fig. S3. (A) Partial GC-MS chromatogram of reaction products of pyruvate þ KCN in carbonate buffer: Temp: ¼ 22 C; initial ph ¼ 10.4; pyruvate ¼ 0.03 M; KCN ¼ 0.07 M. All compounds are their tbdms derivatives. Shown is a total ion chromatogram of a relatively concentrated sample it was chosen to point out compounds of lower abundances. Much greater separation of coeluting compounds is achieved when smaller amounts are injected and/or GC heating rates are slower. Other products are shown in Fig. 2B and listed in Table S2; more compounds are still unidentified. (B) Single ion plot of m z 459 representing citric acid produced in the reaction mix of (A). (C) Chromatogram showing the purity of starting (unlabeled) pyruvate standard and GC retention times of pyruvate products (potential contaminants) had they been present. Labeled pyruvate ( 13 C 1, 13 C 2;3, 13 C 3, and U- 13 C) are of similar purity and also show no reaction products as contaminants. 3of5

4 Fig. S4. Spectra of standard citrate (tbdms) and the citrate obtained from the reaction of 13 C-labeled pyruvate with oxaloacetate. (A) Standard citrate. (B) Spectrum of citrate produced from the reaction of 13 C 2;3 -labeled pyruvate (0.82 M) with unlabeled oxaloacetate (0.84 M) (12 d at 22 C in carbonate). (C) Spectrum of citrate produced from the reaction of U 13 C-labeled pyruvate (0.15 M) with unlabeled oxaloacetate (0.12 M) (5 d at 22 C in carbonate). Ions 591 (M þ -57) and 459 (M þ -57-HO tbdms) represent completely unlabeled citrate. (B and C) show the same mass increase (up to 593 amu) in citrate indicating that the carboxyl carbon is lost in citrate formation. This observation was confirmed when the reaction of 13 C 1 -labeled pyruvate and oxaloacetate (not shown) showed no increase in citrate mass. Oxaloacetate produces significant amounts of its own pyruvate (i.e., the two are in equilibrium), the two compounds then give unlabeled citrate. This fact, and the different reaction conditions of (B and C), account for the lower relative abundances of ions 635 and 593 in C. 4of5

5 Table S1. Definitively identified compounds in carbonaceous meteorites and their concentrations (where measured) Compound (acid) Amount (meteorite*) δ 13 C( ) Keto acids Pyruvic 15 nmole g (ALH) Acetoacetic Levulinic 45 nmole g (ALH),5.4 nmole g (Mur) 17.04(δD¼425 ) 3-Methyl-4-oxopentanoic 5-Oxohexanoic Oxoheptanoic Oxoaoctanoic α-keto glutaric Pyruvic dimer Hydroxy tricarbox. acids HETA Citric 55 pmole g (Mur) Isocitric Tricarbox. acids Tricarballylic 2 nmole g (ALH), 371 pmole g (Mur) 2-Methyl-1,2,3-propanetricarboxylic 1,2,4-Butanetricarboxylic Tetracarboxylic 1,2,3,4-butane tertacarboxylic Several more compounds in each class are not indicated but tentatively identified (Fig. S1A) by their mass spectra. *ALH = Alan Hills 83102; Mur = Murchison Table S2. Compounds indentified as pyruvate reaction products after 7 d at 2 C or 22 C in carbonate/kcn solutions Compound Relative response 2-Ketoglutaric acid tr 3-ketogluataric acid tr Acetoacetic acid 0.5 Fumaric acid 0.5 Citric acid 0.5 Succinic acid Methyl succinic acid 0.7 Mesaconic acid 0.8 Itaconic acid 0.8 Oxaloacetic acid 0.9 Citraconic acid 1.0 Tricarballylic acid 1.0 HETA 1.2 Aconitic acid* 1.9 Lactamide 2.1 Lactic acid 2.9 Alanine 3.3 Glycolic acid 3.8 Urea 4.3 Oxalic acid 6.2 Pyruvic dimer Hydroxy-2-methyl malonic acid 15.2 Citramalic acid 17.4 CN- is not required for the formation of several compounds as indicated in Fig. 2B. Shown are the relative total-ion responses (GC-MS) of compounds (in one sample) after a selected ion search of each. The ratios should be considered as qualitative: comparison between compounds of similar size and functional groups (e.g., fumaric acid/succinic acid and HETA/citric acid) are more valid. The mole percent yield relative to initial pyruvate is less than 1% for the compounds with lower responses, however, samples of much longer reaction times (several months) have not yet been analyzed. The relative and absolute abundances of compounds can change dramatically depending on factors such as concentration, the percent (added) peroxide, etc. tr = signal not measured in this particular sample due to low abundance. *Cis/trans identities and ratios not determined. 5of5