Sugar in the primordial soup

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

• Life from the Soup
• Proteins versus RNA
• Prebiotic syntheses of amino acids nucleobases
• Prebiotic synthesis of sugars
• Sugar in space
• Conclusion

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Life on Earth
Now ?
? 0.7?109 yrs ago Multicellular organisms
? 1.2?109 yrs ago Eukaryotic organisms
? 3.5?109 yrs ago Prokaryotic organisms
Prebiotic
? 4.6?109 yrs ago Formation of Earth
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What started life?
What compounds were present in the
beginning? What compounds/reactions are required
now?
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The primordial soup
N2
CH3CN
CH2O
CH4
HCCCN
CO2
CH2CHCN
NH3
CO
NCCN
H2O
HCN
SO2
Note no photosynthesis - no O2!
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Natural products
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Some are more important!
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The essentials of (modern) life
Proteins composed of amino acids catalyse
reactions RNA composed of nucleobases, ribose
and phosphate carry genetic information
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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
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Protein
aminoacid
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Prebiotic amino acid syntheses
alanine 1,7
glycine 2,1
S.L. Miller Science 117 (1952) 528-529 J. Am.
Chem. Soc. 77 (1955) 2351-2361
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RNA
phosphodiester
nucleobase
ribose
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Prebiotic nucleobase syntheses
J. Oró, Nature 191 (1961) 1193-1194
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Common monosaccharides
aldohexoses
ketohexose
aldopentoses




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Prebiotic carbohydrate synthesisThe Formose
reaction
A. Butlerow, Liebigs Ann. Chem. 53 (1861)
295-298 O. Leow, J. prakt. Chem. 33 (1886) 321-351
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Some of the reactions involved
Cannizzaro de Bruyn-van Ekenstein Aldol
condensation Retro-aldol
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Cannizzaro reaction
Cannizzaro, Ann. 88 (1853) 129-
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de Bruyn-van Ekenstein rearrangement
de Bruyn, Rec. Trav. Chim. 14 (1895) 150- Evans,
Chem. Rev. 31 (1942) 537-559
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de Bruyn-van Ekenstein mechanism
Glucose
Mannose
Fructose
1,2-Enediol
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The first step...
formate
methanol
glycolaldehyde
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Aldol condensation
glyceraldehyde
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de Bruyn-van Ekenstein
glyceraldehyde
dihydroxyacetone
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C3C1 ? C2C2
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Autocatalyticcycle
very slow
C1
C1
C2
C1
C2
fast
C3
C4
C1
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The result
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Sugars in formose(55 total yield of sugars)
Aldopentoses 7 (1.4 ribose)
Ketopentoses 8
Aldohexoses 18
Ketohexoses 18
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Open chain forms
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Tautomers of D-ribose
Cyclic forms (99,9)
Acyclic forms (0,1)
a-furanose
b-furanose
hydrate
aldehyde
b-pyranose
a-pyranose
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Problems
Much more hexoses than pentoses Very little
ribose Racemic mixture of sugars
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dihydroxyacetone
D-sorbose 26
D-fructose 34
D-glyceraldehyde
H.O.L. Fischer E. Baer, Helv. Chim. Acta 19
(1936) 519-532
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Glycolaldehyde phosphate 1
Müller et al., Helv. Chim. Acta 73 (1990) 1410
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Glycolaldehyde phosphate 2
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Extraterrestial compounds
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Aminoacids
12 not found in proteins
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Carbohydrates
aldonic acids alditols
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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.