The document discusses the prebiotic synthesis of sugars and other biomolecules that could have been present on the early Earth and formed the building blocks of life. It describes the formose reaction, which demonstrated the production of various sugars including ribose from simple compounds like formaldehyde and glycolaldehyde. However, the formose reaction produced more hexoses than pentoses and resulted in a racemic mixture of sugars. The document also discusses prebiotic synthesis of amino acids and nucleobases and concludes that while the basic building blocks of proteins and RNA could have formed, the conditions required were incompatible and did not occur in the same place or reaction conditions.

1. Sugar in the primordial soup The formose reaction and the origin of life

2. Content Life from the Soup Proteins versus RNA Prebiotic syntheses of amino acids & nucleobases Prebiotic synthesis of sugars Sugar in space Conclusion

3. Life on Earth  4.6  10 9 yrs ago – Formation of Earth  3.5  10 9 yrs ago – Prokaryotic organisms Now   1.2  10 9 yrs ago – Eukaryotic organisms  0.7  10 9 yrs ago – Multicellular organisms Prebiotic

4. What started life? What compounds were present in the beginning? What compounds/reactions are required now?

5. The primordial ”soup” CO 2 N 2 CO SO 2 CH 2 O CH 4 Note: no photosynthesis - no O 2 ! NH 3 HCN CH 3 CN CH 2 CHCN HCCCN NCCN H 2 O

6. Natural products Aminoacids Steroids Terpenes Lipids Purines Polyketides Carbohydrates Alkaloids Pyrimidines

7. Some are more important! Aminoacids Steroids Terpenes Lipids Purines Polyketides Carbohydrates Alkaloids Pyrimidines

8. The essentials of (modern) life Proteins composed of amino acids catalyse reactions RNA composed of nucleobases, ribose and phosphate carry genetic information

9. Which was first, RNA or proteins? Proteins – superior catalysts, simple building blocks, stable RNA – can be catalysts, complex building blocks, unstable but can replicate themselves

10. Protein aminoacid

11. Prebiotic amino acid syntheses S.L. Miller Science 117 (1952) 528-529 J. Am. Chem. Soc. 77 (1955) 2351-2361 glycine 2,1% alanine 1,7%

12. RNA ribose nucleobase phosphodiester

13. Prebiotic nucleobase syntheses J. Oró, Nature 191 (1961) 1193-1194

14. Common monosaccharides aldopentoses aldohexoses ketohexose glucose mannose ribose arabinose fructose

15. Prebiotic carbohydrate synthesis: The Formose reaction A. Butlerow, Liebigs Ann. Chem. 53 (1861) 295-298 O. Leow, J. prakt. Chem. 33 (1886) 321-351

16. Some of the reactions involved Cannizzaro de Bruyn-van Ekenstein Aldol condensation Retro-aldol

17. Cannizzaro reaction Cannizzaro, Ann. 88 (1853) 129-

18. de Bruyn-van Ekenstein rearrangement de Bruyn, Rec. Trav. Chim. 14 (1895) 150- Evans, Chem. Rev. 31 (1942) 537-559

19. de Bruyn-van Ekenstein mechanism Glucose Mannose Fructose 1,2-Enediol

20. The first step... formate methanol glycolaldehyde

21. Aldol condensation glyceraldehyde

22. de Bruyn-van Ekenstein glyceraldehyde dihydroxyacetone

23. C 3 +C 1  C 2 +C 2

24. Autocatalytic cycle C 2 C 2 C 3 C 4 C 1 C 1 C 1 C 1 very slow fast

25. The result:

26. Sugars in formose (55% total yield of sugars) Aldopentoses 7% (1.4% ribose) Aldohexoses 18% Ketopentoses 8% Ketohexoses 18%

27. Open chain forms 0.3-0.7% 0.002-0.1% hexoses 8-22% 0.1-0.2% pentoses 100% 11-16% tetroses ketoses aldoses

28. Tautomers of D-ribose Cyclic forms (99,9%) Acyclic forms (0,1%)  -furanose  -furanose  -pyranose  -pyranose hydrate aldehyde

29. Problems Much more hexoses than pentoses Very little ribose Racemic mixture of sugars

30. D-glyceraldehyde dihydroxyacetone D-sorbose 26% D-fructose 34% H.O.L. Fischer & E. Baer, Helv. Chim. Acta 19 (1936) 519-532

31. Glycolaldehyde phosphate 1 Müller et al., Helv. Chim. Acta 73 (1990) 1410

32. Glycolaldehyde phosphate 2

33. Extraterrestial compounds Aminoacids Carbohydrates Pyrimidines Purines 60 ppm 60 0.06 1.2

34. Aminoacids +12 not found in proteins Gly Ala Glu Val Pro Asp Leu

35. Carbohydrates + aldonic acids & alditols Mannose Xylose Glucose Arabinose Dihydroxyacetone

36. Conclusion The basic building blocks of proteins and RNA can be prepared from compounds expected to be present on early Earth. The conditions to make them are incompatible, i.e. they can not be formed under the same reaction conditions and in the same place. The strongest proof that they could have been formed prebiotically is their presence in extraterrestrial matter.