Dihydroxybutanoic acids

When a molecule contains two chirality centers as does 2 3 dihydroxybutanoic acid how many stereoisomers are possible ... 

Fischer projections of the stereoisomeric 2 3 dihydroxybutanoic acids compounds I and II are erythro stereoisomers and III and IV are threo... 

For example, syn dihydroxylation of frans-crotonic acid gives the two enantiomers of the threo diastereomer of 2,3-dihydroxybutanoic acid. The same reaction with m-crotonic acid gives the erythro diastereomer of the product. 

Table XI lists results on acyclic diols whose structures cannot be characterized into one of the foregoing categories. The observations on the benzy-lation of the dibutylstannylene acetal of 2,3-dihydroxybutanoic acid derivatives in DMF in the presence of cesium fluoride, where more product is...

The acids (IVab) produced from both the barium permanganate reaction and also from treatment with the oxidizing agent osmium tetroxide were found to be identical, as were their phenylhydrazides and these, in turn, were found to differ from the acids (Illab) formed by the hypochlorous acid method. These acids (Illab, IVab) were therefore considered by Glattfeld and Woodruff to be the two theoretically possible dl dihydroxy acids of the 2,3-dihydroxybutanoic acids. 

FIGURE 7.9 Stereoisomeric 2,3-dihydroxybutanoic acids. Stereoisomers I and II are enantiomers. Stereoisomers III and IV are enantiomers. All other relationships are diastereomeric (see text). 

FIGURE 7.10 Representations of (2/ ,3/ )-dihydroxybutanoic acid, (a) The staggered conformation is the most stable but is not properly arranged to show stereochemistry according to the Fischer projection method. (6) Rotation about the C-2—C-3 bond gives the eclipsed conformation, and projection of the eclipsed conformation onto the page gives (c) a correct Fischer projection. 

Dihydroxyacid dehydratase (E.C. 4.2.1.9) is a ubiquitous enzyme that is involved in the biosynthesis of the branched-chain amino acids (lie, Leu and Val) and of pantothenic acid and coenzyme A. The enzyme catalyzes the elimination of water from 2,3-dihydroxyalkanoic acids (23) to 2-hydroxy-2-alkenoic acids (24), which tautomerize to 2-ketoalkanoic acids (25). The enzyme from spinach has the highest activity towards 2,3-dihydroxy-3-methylbutanoic acid (Val precursor, Scheme 11.5-4) but also accepts other substrates1341. Thus, 2,3-dihydroxybutanoic acid, 3-cyclopropyl-2,3-dihydroxybutanoic add as well as 2,3-dihydroxy-3-methylpentanoic acid are substrates. With the latter substrate a slight preference for (2R,3S)-2,3-dihydroxy-... 

Orgaific chemists use an informal nomenclature system based on Fischer projections to distinguish between diastereomers. When the carbon chain is vertical and like substituents are on the same side of the Fischer projection, the molecule is described as the erythro diastereomer. When like substituents are on opposite sides of the Fischer projection, the molecule is described as the threo diastereomer. Thus, as seen in the Fischer projections of the stereoisomeric 2,3-dihydroxybutanoic acids, compounds I and II are erythro stereoisomers and III and IV are threo. 

Assign the / or S configuration to the chirality centers in the four isomeric 2,3-dihydroxybutanoic acids shown in Fischer projections. Consult Figure 7.7 to check your answers. 

In Section 7.5, the term relative configuration was used to describe the stereochemical relationship between a single chirality center in one molecule to a chirality center in a different molecule. Relative configuration is also used to describe the way multiple chirality centers within the same molecule are related. The two erythro stereoisomers of 2,3-dihydroxybutanoic acid possess the same relative configuration. The relationship of one chirality center to the other is the same in both, but different from that in the threo stereoisomer. 

Amino-ix,fi-dihydroxy-9il-purine-9-buta-noic acid, 9CI. 4-(6-Amiru>-9H-purin-9-yl)-4-deoxyerythronic acid, SCI. 4-(9-Adeninyl)-2,3-dihydroxybutanoic acid. Lentysine. Lentinacin... 

Dimethyl tartrate 6.260) is also an important chiral template. The first step was protection of the diol moiety to give acetonide 6.261. A multi-step transformation followed which gave 4-amino-2,3-dihydroxybutanoic acid, 6.262. This dihy-droxyamino acid was converted to anthopleurine (4-amino-2,3-dihydroxybutanoic acid, or 4-[N,N,N-trimethylammonium]-2,3-dihydroxybutanoic acid, 6.263), an alarm pheromone of the sea anemone Anthopleura elegantissima. ... 

Deprotection provided 4-amino-4-deoxy-D-erythronic acid (4-amino-2,3-dihydroxybutanoic acid, 6.282), which was used in a synthesis of eritadenine.i59 This is a structural isomer of 6.262 from above. 

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