Download - Sugar in the Primordial Soup
Sugar in the primordial soupThe formose reaction and the origin of life
Content
• Life from the Soup• Proteins versus RNA• Prebiotic syntheses of amino acids &
nucleobases• Prebiotic synthesis of sugars• Sugar in space• Conclusion
Life on Earth
4.6109 yrs ago – Formation of Earth
3.5109 yrs ago – Prokaryotic organisms
Now
1.2109 yrs ago – Eukaryotic organisms 0.7109 yrs ago – Multicellular organisms
Prebiotic
What started life?
What compounds were present in the beginning?
What compounds/reactions are required now?
The primordial ”soup”
CO2
N2
CO
SO2
CH2O CH4
Note: no photosynthesis - no O2!
NH3
HCN
CH3CN
CH2CHCN HCCCN
NCCNH2O
Aminoacids
Natural products
Steroids
TerpenesLipids
Purines Polyketides
CarbohydratesAlkaloidsPyrimidines
Aminoacids
Some are more important!
Steroids
TerpenesLipids
Purines Polyketides
CarbohydratesAlkaloidsPyrimidines
The essentials of (modern) life
Proteinscomposed of amino acidscatalyse reactions
RNAcomposed of nucleobases,ribose and phosphatecarry genetic information
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
H2N
NH
HN
O
O
O
OH
OH
Protein
aminoacid
Prebiotic amino acid syntheses
S.L. MillerScience 117 (1952) 528-529J. Am. Chem. Soc. 77 (1955) 2351-2361
glycine 2,1%
alanine 1,7%
O
O OH
O
P O
O
O N
NN
N
NH2
RNA
ribose
nucleobase
phosphodiester
Prebiotic nucleobase syntheses
J. Oró, Nature 191 (1961) 1193-1194
Common monosaccharides
H
CHO
OH
HHO
OHH
OHH
CH2OH
glucose
HO
CHO
H
HHO
OHH
OHH
CH2OH
mannose
H
CHO
OH
OHH
OHH
CH2OH
ribose
HO
CHO
H
OHH
OHH
CH2OH
arabinose
CH2OH
O
HHO
OHH
OHH
CH2OH
fructose
aldopentoses aldohexoses ketohexose
Prebiotic carbohydrate synthesis:
The Formose reaction
A. Butlerow, Liebigs Ann. Chem. 53 (1861) 295-298O. Leow, J. prakt. Chem. 33 (1886) 321-351
CH2O (CH2O)nOH
Some of the reactions involved
Cannizzaro
de Bruyn-van Ekenstein
Aldol condensation
Retro-aldol
Cannizzaro reaction
Cannizzaro, Ann. 88 (1853) 129-
H
O OH
H
OHO H
O
O
OH
+ H
OH
de Bruyn-van Ekenstein rearrangement
de Bruyn, Rec. Trav. Chim. 14 (1895) 150-Evans, Chem. Rev. 31 (1942) 537-559
OHO
HO
OH
HO
OHO
HO
HO OH
O
OHHO
OH
OH
OH
OH
OH
D-Glucose 66% D-Mannose 3%
D-Fructose 31%
de Bruyn-van Ekenstein mechanismGlucose Mannose Fructose
1,2-Enediol
CHO
OHH
HHO
H OH
OHH
CH2OH
CHO
HHO
HHO
H OH
OHH
CH2OH
CH2OH
O
HHO
H OH
OHH
CH2OH
OH
HHO
H OH
OHH
CH2OH
H OH
H H
HO O
H H
O
H O
O
H OH
H H
+
H
HOOH
H H
O
H
HO OH
O
H
HOH
H
O
H H
The first step...
formate methanol
glycolaldehyde
Aldol condensation
H
O
OHOH
H
O
OHH H
O
H
O
OH
OH
glyceraldehyde
de Bruyn-van Ekenstein
OHH
O
OH
OH OHOH
H
OH
OH
OH
O
OH
glyceraldehyde dihydroxyacetone
C3+C1 C2+C2
HO OH
O
H H
O
HO
O
OH
OH
H
OH
OH
OH
O
H
OH
O
OH
O
H
Autocatalyticcycle
C2C2
C3C4
C1C1
C1
C1
very slow
fast
The result:
Sugars in formose(55% total yield of sugars)
Aldopentoses 7%(1.4% ribose)
Aldohexoses 18%
Ketopentoses 8%
Ketohexoses 18%
Open chain forms
aldoses ketoses
tetroses 11-16% 100%
pentoses 0.1-0.2% 8-22%
hexoses 0.002-0.1% 0.3-0.7%
Tautomers of D-ribose
OHO
OH OH
OH
OHO
OH
OHOH
H OH
OHH
OHH
CH2OH
O H
H OH
OHH
OHH
CH2OH
HO OHOH
HO OH
O
OH
HO OH
O
OHOH
Cyclic forms (99,9%)
Acyclic forms (0,1%)
-furanose -furanose
-pyranose-pyranose
hydrate aldehyde
Problems
Much more hexoses than pentoses
Very little ribose
Racemic mixture of sugars
OH
CH2OH
O
CH2OH
O
OH
CH2OH
CH2OH
O
OH
HO
OH
CH2OH
CH2OH
O
OH
CH2OH
HO
OH+
D-glyceraldehyde
dihydroxyacetone
D-sorbose26%
D-fructose34%
H.O.L. Fischer & E. Baer, Helv. Chim. Acta 19 (1936) 519-532
Glycolaldehyde phosphate 1CHO
CH2OPO3
CHO
CHOPO3
CHOH
CHOPO3
CH2OPO3
CHOH
CHO
CH2OPO3
CHO
CH2OPO3
Müller et al., Helv. Chim. Acta 73 (1990) 1410
Glycolaldehyde phosphate 2CHO
CH2OPO3
CHO
CHOPO3
CHOH
CHOPO3
CH2OH
CHO
CH2OPO3
CH2O
Extraterrestial compounds
AminoacidsCarbohydratesPyrimidinesPurines
60 ppm60 0.06 1.2
Aminoacids
Gly
Ala
Glu
Val
Pro
Asp
Leu
+12 not found in proteins
Carbohydrates
+ aldonic acids & alditols
Mannose
Xylose
Glucose
Arabinose
Dihydroxyacetone
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.