Carbohydrates formose reaction

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... 

Although there are a number of inefficient steps in most proposed prebiotic syntheses of ribotides, the major objection to RNA as the primogenitor of life has been the relatively small yield of ribose in the formose reaction, a simple condensation of glycoaldehyde. Muller et a/.,18 however, have discovered a variation of the formose reaction that produces a limited mix of pentose diphosphates in which the ribose forms predominate (52 14 23 11, ribose arabinose lyxose xylose). Although many critical chemical roadblocks remain (such as the extremely low yield of pyrimidine nucleosides following the condensation of ribose and free bases), this advance belies the previously held view that products of the formose reaction are necessarily so chemically diverse that they are the carbohydrate analog of petroleum. 19... 

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. 

Shigemasa, Y, Ueda, T, Saimoto, H, First synthesis of DL-2-C-hydroxymethyl-3-pentulose in the formose reaction, J. Carbohydr. Chem., 8, 669-673, 1989. 

The classical formose reaction gives a very large number of carbohydrates including branched-chain isomers [17,18,19]. Straight-chain carbohydrates such as trioses, tetroses, pentoses, and hexoses are readily obtained in good yield by a reaction of formaldehyde with syngas in the presence of RhCl(CO)(PPh3)2 and tertiary amines [37]. 

This holds true for amino acids, nucleobases, and carbohydrates. Even within one class of the biogenic molecules, two or more independent routes developed. As illustrated by the formose reaction, chiral sugar molecules formed when catalyzed by an appropriate chiral amino acid (to be discussed further below). 

The most dubious approximation made in developing the mechanism was in describing the reaction intermediates and products as one species each, namely, A and A +i. Undoubtedly, the formose reaction is a complex network whose overall behavior is a function of the concentrations of many individual species. In fact, the formose product might be regarded as the carbohydrate analog of petroleum, in that it contains so many compounds of different molecular weight and isomeric structure. 

By using similar techniques, the structures of Cj, Ce, and C7 branched-chain carbohydrate compounds produced in the formose reaction were also elucidated. Figure 18 compares 2-C-( hydroxymethyl )glyceraldehyde from formose with a reference sample of erythrose [as their per(tri-methylsilyl) derivatives]. The mass-spectral fragmentation pattern of... 

The formose reaction can be considered a unique method for producing branched-chain carbohydrates. The presence of these species may account for the observed toxicity of formose syrups. 

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. 

A review in Russian on the synthesis of carbohydrates from formaldehyde has appeared. An investigation of the formose reaction by g.c.-n.m.r. has shown that intermediate glycoaldehyde, glyceraldehyde, and dihydroxyacetone are present as mixtures of monomers, e.g. hydroxy carbonyl compounds, epoxides and hydrates, and dimers such as half and full acetals. Further study of the barium chloride-catalysed formose reaction at pH 12 has shown that the main product forming 33% of the total sugars is the branched pentulose (1). The sugar yield reached a constant value at 70% completion of the reaction, i.e., within... 

GC-MS has been widely used in the analysis of carbohydrate materials. The photosynthetic incorporation of C02 into carbohydrates by corn and soyabean plants can be conveniently monitored by this technique using trimethylsilylated oxime derivatives,22 gnd a capillary GC-CI MS procedure has been used to analyse mixtures of pentosesand hexoses via trifluoro-acetylated oxime derivatives. GC-MS data have also been recorded for the products of the formose reaction,permethylated trisaccharide alditols derived from sialic acid-containing glycopeptides, 6 cytokinin ribonucleosides, 7 methylated and... 

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) ... 

---