Sugars carbon atom numbering

The six-carbon sugar a-galactose is identical to a-glucose except at carbon atom number 4, where the orientations are different. Draw the molecular structure of a-galactose. Simplify the stmcture by using flat rings rather than the true three-dimensional forms. 

Although the orthocarboxylic acids, R—C(OH)3, are unstable, many of their derivatives are known, stable compounds. The known carbohydrate orthoesters are all derived from the structure that results when two of the three hydroxyl groups of an orthoacid are involved in ester formation with two hydroxyl groups of the sugar molecule. General formula A represents those types which are of particular interest in the field of carbohydrates. The two adjacent carbon atoms of the five-membered ring constitute carbon atoms number 1 and 2 of an aldose and either 1 and 2, or 2 and 3 of a ketose. In certain instances it has been... 

In the terminology suggested by Reeves (see Ref. 1), the mirror image of VII, /3-L-glucopyranose, has the 1C conformation. The designation Cl (italics) is not to be confused with Cl (no italics) for carbon atom number one of a sugar chain. 

The individual DNA molcule which localized in eukaryotic chromosomes are large polymers and they contain a linear backbone of alternating sugar and phosphate residues. DNA molecule includes the five carbon sugar "deoxyribose," and consecutive sugar structures are linked by covalent phosphodiester bridge. Covalently bonded to carbon atom number V (one prime) of each sugar is a... 

We must now consider which functional groups are involved in the assembly of these compounds. In the case of the formation of a nucleoside, the nitrogen atom number 3 of a pyrimidine base or the nitrogen atom number 9 of a purine base becomes linked to the carbon atom number 1 of the pentose sugar, with the elimination of water. According to the conventions of sugar chemistry the carbon atom number 1... 

The simple sugars or monosaccharides are polyhydroxy aldehydes or ketones, and belong to Solubility Group II. They are termed tetroses, pentoses, hexoses. etc. according to the number of carbon atoms in the long chain constituting the molecule, and aldoses or ketoses if they are aldehydes or ketones. Most of the monosaccharides that occur in nature are pentoses and hexoses. 

Sugars have large numbers of stereoisomers because they contain several asymmetric carbon atoms. 

In such names, numerals will refer to carbon atoms of the sugar moiety, and primed numerals to the positions on the nitrogenous base compare Ref. 1, pp. 200 and 208. Pyrimidines and purines are numbered by the Chem. Abstracts system. 

Figure 20.15 Diagram of a small portion of the DNA duplex to illustrate antiparallel nature of the two DNA strands. The bonds = between bases are the hydrogen bonds. The prime ( ) is necessary since the atoms in the base are numbered as are the atoms in the sugar. Numbers in the latter are therefore distinguished by a superscript prime on the pertinent carbon atom. The numbers in this diagram are indicated on only one ribose to keep its diagram in the simplest form.

Acetylenic precursors employed in the syntheses of sugars may be divided into three groups (a) aldehydes (usually in the form of acetals), (b) alkyl alkynyl ethers, and (c) alkynols or alkynediols. Some of them are commercially available (for example, 2-butyne-l,4-diol), and others are prepared by Grignard-type reactions between 1-alkynylmag-nesium halides or lithium alkynes and suitable aldehydes, ketones, or epoxides. In this way, the synthesis of substrates having the desired number of carbon atoms, as well as the necessary functional groups, can be achieved. The next step consists in partial saturation of the triple bond to afford the desired cis- or trans-alkene. ct.s-Alkene systems... 

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