Prebiotic Synthesis of Carbohydrates

There is a debate over whether the classical formose reaction [3-5] might have played a role in the prebiotic synthesis of carbohydrates. When a slurry of carbonate-apatite is boiled with 0.5 M formaldehyde at pH 8.5 a yield lower then 40% in sugars is reached after a few hours. 

HCOH tetroses HCOH pentoses SCHEME 13.4 Reaction of carbon atoms with water. Formation of aldoses. 

SCHEME 13.6 Sulfite anion and aldehyde adduct formation. A possible concentration process in double-layer hydroxide minerals such as Mg2Al(0H) [S03H (H20)2]. 

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The Formose condensation, discovered by Butlerow (1861), remains in its various modifications the only candidate for the prebiotic synthesis of carbohydrates. The reaction is autocatalytic and involves the following series of reactions (Breslow, 1959) ... 

The formose reaction has remained a subject of current interest in connection with possibility of its industrial application as well as with the speculations on the prebiotic synthesis of carbohydrates. Although the complex mixture of sugars and alditols produced in the base catalyzed condensation of formaldehyde. 

Carbohydrates are still difficult to deal with in prebiotic chemistry although the first laboratory syntheses of carbohydrates were described more than 150 years ago, their prebiotic synthesis is still unclear. 

Weber [61,62] has developed in the context of prebiotic chemistry an original pathway for a-aminothioester synthesis [180], which can start from hydroxyaldehydes 30 intermediates in the formose reaction (a likely prebiotic pathway to carbohydrates). Obviously, thioesters themselves are not observed as products because of their fast hydrolysis in the medium, but they could be converted into peptide bonds in the presence of amino acids or peptide free amino groups, and into mixed anhydride with phosphoric acid in the presence of inorganic phosphate. The reaction involves two key-steps the condensation of ammonia and of the mercaptan on a-keto aldehyde 31... 

There are a number of possible ways to stabilize sugars the most interesting one is to attach the sugar to a purine or pyrimidine, i.e., by converting the carbohydrate to a glycoside, but the synthesis of nucleosides is difficult under plausible prebiotic conditions. It has therefore been suggested that ribonucleotides could not have been the first components of prebiotic informational macromolecules (59). This has led to propositions of a number of possible substitutes for ribose in nucleic acid analogues, in what has been dubbed the "pie-RNA World" (60). 

Isomaltooligosaccharides (as mixtures of different a-glucooligosaccharides) are produced in part by dextransucrases using sucrose as the substrate and maltose as an acceptor. They have been used as sweeteners in Europe and Japan for years, mainly in the field of prebiotics, and dermocosmetics [11-13]. Several different methods can be used to produce them by using such carbohydrates as sucrose, maltose, starch, and dextran. For the industrial production of a-glucooligosaccharides with sucrose as the substrate and maltose as the acceptor by one specific dextransucrase (of L. mesenteroides NRRL B-1299), the kinetic behavior of the enzyme has been characterized in order to optimize the synthesis [14]. 

Kofoed J, Reymond JL, Darbre T Prebiotic carbohydrate synthesis zinc-proline catalyzes direct aqueous aldol reactions of alpha-hydroxy aldehydes and ketones. Organic Biomolecular Chemistry 2005, 3(10) 1850-1855. 

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