Sugar prebiotic

Prebiotic chemistry of natural heterocycles, among them purines, pyrimidines, sugars, and riboflavin 97T11493. 

Earlier studies showed that reactions of sugars with ammonia lead to small molecules such as amines or organic acids. A. L. Weber has reported important autocatalytic processes occurring when trioses are allowed to react with ammonia under anaerobic conditions, such reactions provide products which are autocatalyt-ically active. Their autocatalytic activity was determined directly by investigating their effect on an identical triose-ammonia reaction. Both an increase in the triose degradation rate and an increased rate of synthesis of pyruvate, the dehydration product of the triose, were observed. Such processes may have been of importance for prebiotic chemistry occurring on the primeval Earth (Weber, 2007). 

The formation of sugars from the reaction of formaldehyde under alkaline conditions was discovered in 1861 and is known as the formose reaction , although it is not understood fully (Figure 8.7). It requires the presence of suitable inorganic catalysts such as Ca(OH)2 or CaCOr, either of which may be found on a prebiotic Earth. The reaction is autocatalytic and produces over 40 different types of sugars, some rings, some long chains. 

Moderately simple syntheses have been performed for the purines cytosine and uracil but nothing seems to work as a prebiotic synthesis of the pyrimidines. Then adding the sugar ribose to the base makes them nucleosides and one phosphoric acid residue makes it a nucleotide, or specifically a mononucleotide a rare but curiously important sequence of events in present-day life but perhaps not for prebiotic chemistry and early life forms. 

Endogenous organic synthesis Urey-Miller experiments as a source of prebiotic molecules via the Strecker synthesis for amino acids, HCN polymerisation for purines and pyrimidines and the formose reaction for sugars... 

Formose reaction A prebiotic reaction producing sugars but little ribose. 

It should be kept in mind that these prebiotic syntheses concern only the bases, and not the mononucleotides of the nucleic acids. The mononucleotide consists of three moieties attached to each other - the base, the phosphate, and the sugar - and we do not yet know how this prebiotic synthesis may have taken place. 

It is of course surprising that amino acids can be obtained via the Strecker synthesis, purines from the condensation of HCN, pyrimidines from the reaction of cyanoacetilene with urea, and sugars from the autocatalytic condensation of formaldehyde. The synthesis of chemical constiments of contemporary organisms by non-enzymatic processes under laboratory conditions does not necessarily imply that they were either essential for the origin of life or available in the primitive environment. However, the significance of prebiotic simulation experiments is... 

There is another point about the thermodynamic stability of prebiotic compounds. This is the fact that a series of thermodynamically very stable molecules seem to have been ignored in the course of prebiotic molecular evolution as building blocks of living structures. Take sugars, for example six-membered rings have not been used for the construction of nucleic acids, where only o-ribose takes the stage. Furthermore, only two types of purine and only two of the pyrimidine bases have been utilized among the many possible nucleic acids. Actually one could make a... 

Decker, R, Schweer, H., and Pohlmann, R. (1982). Identiflcation of formose sugars, presumable prebiotic metabolites, using capillary gas chromatography/gas chromatography-mass spectrometry of n-butoxime trifluoroacetates on OV-225. J. Chromatogr, 225, 281-91. 

Hydrogen cyanide and methanal are especially reasonable starting materials for the prebiotic synthesis of amino acids, purine and pyrimidine bases, ribose and other sugars. Formation of glycine, for example, could have occurred by a Strecker synthesis (Section 25-6), whereby ammonia adds to methanal in the... 

Inulin has no sweetness and possesses a bland taste. Physiologically, inulin behaves as a dietary fibre. At relatively high dose levels (15-40 g/day) it can have a prebiotic effect (i.e. it can selectively promote the growth of beneficial bacteria in the colon) and at high dose levels it may also have a laxative effect (Kolida el al., 2002). This is dependent on the specific composition of the product and the degree of polymerisation, which can vary. The caloric value for inulin is 1 kcal/g. Its use in soft drinks is as a fibre source, prebiotic and partial sugar replacer. 

FOS and oligofuctose are fructose oligomers that are either produced by enzymic conversion of sugar or extracted from chicory, as inulin, and then hydrolysed. These products behave as soluble fibres and prebiotics. In acid conditions, they can hydrolyse, but are usually sufficiently stable for short-shelf-life juices, near-water products with low acid levels or powdered soft drinks. Prebiotic activity varies with preparation and required daily dose can be as low as 2.5-5.0 g/day for shorter chain FOS preparations (DP 2 1). Some positive effects on magnesium absorption and calcium absorption (in some populations) have also been shown (Beghin Meiji, 2001). 

Products are available in dry or syrup form. They have a lower sweetness than sucrose, RS = 0.3-0.6. The caloric value in the EU is 2 kcal/g. They are relatively hygroscopic and have good solubility. Use in soft drinks and juice products is as a sugar replacer, soluble fibre and prebiotic. 

It is currently used to improve mouthfeel and as a soluble fibre, prebiotic and partial sugar replacer in soft drinks. 

Electric discharges acting on a mixture of CO, N2, and H2 are not effective in amino acid synthesis unless the ratio of H2 to CO is greater than about 1.0. Glycine is produced in fair yield, but only small amounts of any higher amino acids are produced. Large amounts of formaldehyde are obtained, however, and formaldehyde is important in the prebiotic synthesis of sugars. 

The above review shows the progress that has been made in the last 30 years. The prebiotic synthesis of amino acids, purines, pyrimidines, and sugars is understood at a basic level, although more details of the reactions are needed. The polymerization processes are less well understood, and while some of them are plausible it is necessary to work them out in greater detail. The template polymerization reactions are an exciting beginning and may show how genetic information started to accumulate. So far the problem of nucleic acid directed enzyme synthesis has not been dealt with on an experimental level. The problems in this area, which are very difficult, are considered by other speakers in this symposium. 

Simple dipeptides bearing a primary amino N-terminus catalyse direct asymmetric intramolecular aldol reactions in up to 99% ee.115 These simple catalysts such as L-Ala-L-Ala and L-Val-L-Phe can also promote the asymmetric formation of sugars, further suggesting a possible role in prebiotic chemistry. 

These carbohydrates may be added to all kinds of foods, such as cereals, cakes, biscuits, and health drinks. They can be extracted from things like chicory root or produced from sugar by the action of specific enzymes. A little FOS is also to be found in bananas, leeks, and wheat, and the other prebiotics also occur naturally, but no fruit or vegetable by itself can supply the 5 g of oligosaccharides needed daily to boost the good bacteria. Indeed the normal person s diet contains only about 2 g of these carbohydrates. 

Phosphorus is abundant on Earth, both as an element (the llth-most abundant atom in Earth s crust) and as phosphate. Meteorites hold a variety of phosphate-containing minerals and some phosphide minerals.10 Scientists at the University of Arizona have recently suggested that Fe3P, the mineral schreibersite, leads to the formation of phosphate and phosphite when corroded in water. Although phosphorylation of alcohols was not demonstrated, mechanistic considerations suggest that it should be possible. It is noteworthy that a clear prebiotic pathway for the chemical incorporation of phosphate into RNA or DNA has not been found. No nucleosides (nucleobases joined to sugars) have been reported from meteorites. Nor has evidence been found in any meteorite of the presence of nucleosides or nucleotides (nucleosides attached to phosphates). That suggests that nucleic acids were first formed as products of metabolism. 

Formamide is itself hydrolyzed by water, meaning that it persists only in a relatively dry environment, such as a desert. Desert environments recently proposed as being potential sites for the prebiotic synthesis of ribose18 may hold formamide as well. Since formamide boils at —400 K, a mixture of formamide and water, if placed in the desert, would lose its water over time and end up as a pool of formamide. Within this pool, many syntheses are thermodynamically favorable polypeptides from amino acids, nucleosides from sugars and bases, nucleotides from nucleosides and inorganic phosphate, and RNA from nucleotides. Indeed, phosphate esters are also spontaneously synthesized. This includes ATP (from ADP and inorganic phosphate), nucleosides (from ribose borates and nucleobases), peptides (from amino acids), and others.19-21... 

Frozen desserts and mouthfeel foam stability fiber and prebiotic Sugar and fat replacement texture and melting synergy 2-10 5-12... 

Baked goods and breads stability fiber and prebiotic Fiber and prebiotic moisture retention sugar replacement 2-15 2-25... 

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