Glyceraldehyde chiral carbon

A method for designating the stereoisomeric configuration of a chiral carbon atom within a molecular entity. The designation d was arbitrarily assigned to (-F)-glycer-aldehyde, and (-)-glyceraldehyde was assigned the label... 

The nomenclature and classification of monosaccharides is further complicated by the presence of chiral carbons within monosaccharides. In the late nineteenth century it was ascertained that the configuration of the last chiral carbon in each of the naturally occurring monosaccharides is the same as that for (-i-)-glyceraldehyde. This configuration was designated as D and it was determined that all naturally occurring monosaccharides were in the D configuration. 

D-Glyceraldehyde The hydroxyl group on the chiral carbon is on the right hand side... 

Hydroxyl group at the highest numbered chiral carbon (C-5) is pointing to the right, i.e similar to D-glyceraldehyde... 

All the monosaccharides except dihydroxyacetone contain one or more asymmetric (chiral) carbon atoms and thus occur in optically active isomeric forms (pp. 17-19). The simplest aldose, glyceraldehyde, contains one chiral center (the middle carbon atom) and therefore has two different optical isomers, or enantiomers (Fig. 7-2). 

In all these d isomers, the chiral carbon most distant from the carbonyl carbon has the same configuration as the chiral carbon in D-glyceraldehyde. The sugars named in boxes are the most common in nature you will encounter these again in this and later chapters. 

Glyceraldehyde, CH2OHCHOHCHO, which has one chiral carbon bonded to an aldehyde function, hydrogen, hydroxyl, and hydroxymethyl (CH2OH), is of special interest as the simplest chiral prototype of sugars... 

When there are several chiral carbons in a molecule, the configuration at one center usually is related directly or indirectly to glyceraldehyde, and the configurations at the other centers are determined relative to the first. Thus in the aldehyde form of the important sugar, (+)-glucose, there are four chiral centers, and so there are 24 = 16 possible stereoisomers. The projection formula of the isomer that corresponds to the aldehyde form of natural glucose... 

Glyceraldehyde has only one chiral carbon atom and can exist as two enantiomers, but other sugars have two, three, four, or even more chiral carbons. In general, a compound with n chiral carbon atoms has a maximum of 2n possible isomeric forms. Glucose, for example, has four chiral carbon atoms, so a total of 24 = 16 isomers are possible, differing in the spatial arrangements of the substituents around the chiral carbon atoms. 

It was then possible, by unambiguous chemical interconversion procedures or by physical property comparisons, to relate many compounds having one or more chiral carbons to either of the enantiomers of glyceraldehyde. This enabled a number of chiral compounds to be designated as belonging to the d- or l-... 

Fischer projections are however, unsatisfactory when considering the physical properties and chemical reactivity of monosaccharides for which definitive spatial formulations are necessary. These are given below for D-glyceraldehyde, D-erythrose and D-threose, for which the (/ ,S configuration may be readily assigned at the appropriate chiral carbons. 

C is correct. A pair of enantiomers would be formed bv the addition of one chiral carbon. Only one configuration of glyceraldehyde is used, so that chiral carbon does not increase the number of enantiomers. 

Glyceraldehyde contains a single chiral carbon, located in position 2. All carbohydrates contain chiral carbons. The number of possible isomers is given by 2 . For glyceraldehyde, only two isomers are possible, d and l. For a hexose, on the other hand, which in its open form (Figure 9.2) contains four chiral atoms, the number of isomers is 24 = 16, half of them in the d and half in the l series. The first and last carbons in a carbohydrate molecule, if the open structure (e.g., Figure 9.2) is viewed, are nonchiral. 

The simple aldoses are related to d- and L-glyceraldehyde in that structurally they may be considered to be derived from glyceraldehyde by the introduction of hydroxylated chiral carbon atoms between C-l and C-2 of the glyceraldehyde molecule. Thus, two tetroses result when CHOH is introduced into D-glyceraldehyde ... 

There are two series of simple aldoses a d series and an l series. To determine to which series an aldose belongs, locate the chiral carbon atom most remote from the reducing group and determine its relationship to glyceraldehyde e.g., the sugar shown below, glucose, is called D-glucose ... 

The most common ketose, d-fructose, is shown below. Compare the configuration of the chiral carbon atom most remote from the keto group (C-5) with D-glyceraldehyde. 

Figure 6 Structures of the four stereoisomers of sphingosine. Sphingosine has two chiral carbon atoms (C-2 and C-3). The Fischer projection formula of each structure is also shown, with C-1 at the top, to illustrate the D/L and erythro/threo stereochemical nomenclature. C-3 has an erythro orthreo configuration as it relates to C-2, depending on whether the similar groups (amino and hydroxy) are on the same or opposite side of the Fischer projection. D versus L refers to the configuration at C-2 relative to the configuration of D-glyceraldehyde versus L-glyceraldehyde.

Monosaccharides are identified by their carbonyl functional group (aldehyde or ketone) and by the number of carbon atoms they contain. The simplest monosaccharides are the two trioses glyceraldehyde (an aldotriose) and dihydroxyacetone (aketotriose). Four-, five-, six-, and seven-carbon-containing monosaccharides are called tet-roses, pentoses, hexoses, and heptoses, respectively. Structures of some monosaccharides are shown in Figure 9-1. All monosaccharides, with the exception of dihydroxyacetone, contain at least one asymmetrical or chiral carbon atom, and therefore two or more stereoisomers are... 

Stereoisomers of glyceraldehyde. (a) Perspective formulas showing tetrahedral arrangement of the chiral carbon 2 with four different substituents, (b) Projection formulas in which the horizontal substituents project forward and the vertical substituents project backward from the plane of the page, (c) A common method of representation. 

Monosaccharides have one or more chiral carbon centers and can thereby form enantiomers and diastereomers. Most common monosaccharides are in the D-family. This means that, using D-glyceraldehyde as a starting point, other chiral carbons can be inserted between the carbonyl group and the D- carbon, producing families of... 

Because many biomolecules have more than one chiral carbon, the letters d and L refer only to a molecule s structural relationship to either of the glyceraldehyde isomers, not to the direction in which it rotates plane-polarized light. Most asymmetric molecules found in living organisms occur in only one stereoisomeric form, either D or L. For example, with few exceptions, only L-amino acids are found in proteins. 

In 1891 Emil Fischer devised a nomenclature system that would allow scientists to distinguish between enantiomers. Fischer knew that there are two enantiomers of glyceraldehyde that rotated plane-polarized light in opposite directions. He did not have the sophisticated tools needed to make an absolute connection between the structure and the direction of rotation of plane-polarized light. He simply decided that the (-L) enantiomer would be the one with the hydroxyl group of the chiral carbon on the right ... 

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