Phosphate substituents

As the preceding sections show, the term lipid A does not denote a defined molecular entity but rather a family of structurally closely related but not identical phosphoglycolipids. Their structures may differ in the type and number (one or two) of HexpN residues present in the backbone by the number, location, nature, size, and linkage of acyl residues by the nature of phosphate substituents and finally by the degree of phosphorylation of the backbone. Lipid A components of different bacterial origin are classified in the present article on the basis of structural variations. 

In contrast to the backbone structure which represents a constant portion of lipid A the phosphate groups with their various substituents comprise a variable region of lipid A. This natural, obviously restricted interbacterial diversity of phosphate substituents demonstrates that lipid A s of different origin are distinct in their fine structure. In some cases (like Salmonella and Escherichia) the substitution of the backbone phosphate group is not quantitative. This implies a certain heterogeneity of a given lipopolysaccharide preparation expressed on the level of its lipid A component. 

A convenient enantioselective catalytic oxidation of a variety of differently substituted, cyclic (E) and acyclic (Z)-enol phosphates with (salen)manganese(III) complex has been reported. The influence of electronic and steric effects of the enol phosphate substituents on the stereoselectivity of oxidation has been studied.50... 

In summary, the electrostatic repulsion due to four or more equatorially oriented dianionic phosphates disfavors the 1 ax/5 eq orientation and induces ring flip to the 5 ax/1 eq form. The proclivity toward ring flip is influenced by the number, position, and orientation of dianionic phosphate substituents on the inositol ring the facility for ring flip is as follows (29) > (27) > (31) > (33) > (35). 

PositionAi efei sto, for structure A, the position of the phosphate substituent on the phenyl ring, or for structureB, the nature of X. 

C NMR was a reliable source of detection and identification of carbon nuclei in the saccharide molecule. However, greater quantities were requiredfor ID experiments as compared with H NMR spectroscopy and often extended periods for acquisition (sometimes 3 days) were required. The H- C heteronuclear multiple quantum correlation (HMQC) was one experiment that allowed the assigiunent of carbon resonances, by correlation with their proton nuclei, and where smaller quantities were used. A conscious ID P NMR investigation quickly revealed the presence of phosphate or a 2-aminoethyl phosphate unit in the core OS. 2D H-3 P HMBC NMR spectroscopy was a reliable method for efficient detection and sometimes placement of the phosphate substituents. 

We construct a nucleotide from three components. First, we replace the hydroxy group at Cl in the sugar with one of the base nitrogens. This combination is called a nucleoside. Second, a phosphate substituent is introduced at C5. In this way, we obtain the four nucleotides of both DNA and RNA. The positions on the sugars in nucleosides and nucleotides are designated r, 2, and so forth, to distinguish than from the carbon atoms in the nitrogen heterocycles. 

TTP Tricresyl phosphate, tritolyl phosphate substituents (ANSl/ASTM)... 

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