Polysaccharides phosphoric esters

Many bacterial polysaccharides contain phosphoric ester groups. There is a limited number of examples of monoesters. More common are phosphoric diesters, connecting an amino alcohol or an alditol to the polysaccharide chain. Another possibility is that oligosaccharide or oligosaccharide-alditol repeating units are connected to a polymer by phosphoric diester linkages. In addition to the intracellular teichoic acids, several bacteria, for example, different types of Streptococcus pneumoniae, elaborate extracellular polymers of this type. These polymers are generally discussed in connection with the bacterial polysaccharides. 

A whole class of fascinating, acidic and ester polysaccharides of biological significance awaits exploration by x-ray diffraction. Typical of these compounds are the pneumococcal polysaccharides, whose structures are highly specific, albeit they contain a wide variety of carbohydrate moieties, of which D-glucuronic acid is a common one. Occasionally, a phosphoric ester link between moieties is an integral part of the complex, repeating... 

Phosphoric acid esters of the ketopentose D-ribulose (2) are intermediates in the pentose phosphate pathway (see p.l52) and in photosynthesis (see p.l28). The most widely distributed of the ketohexoses is D-fructose. In free form, it is present in fruit juices and in honey. Bound fructose is found in sucrose (B) and plant polysaccharides (e.g., inulin). 

Ribonucleotides Ribonucleic acid consists of ribonucleosides bonded together into a polymer. This polymer cannot be bonded by glycosidic linkages like those of other polysaccharides because the glycosidic bonds are already used to attach the heterocyclic bases. Instead, the ribonucleoside units are linked by phosphate esters. The 5 -hydroxyl group of each ribofuranoside is esterified by phosphoric acid. A ribonucleoside that is phosphorylated at its 5 carbon is called a ribonucleotide ( tied to phosphate). The four common ribonucleotides, shown in Figure 23-23, are simply phosphorylated versions of the four common ribonucleosides. 

There are many polymers that are suitable for the production of nanoparticles employed for drug delivery, which can generally be divided into two groups natural polymers, e.g., polysaccharides (chitosan), proteins (albumin, gelatin), as well as synthetic polymers, e.g., polyesters (poly(lactic add), poly(glycolic add), poly(hydroxy butyrate), poly-e-caprolactone, poly-p-malic add, poly(dioxanones)) polyanhydrides (poly(adipic add)) polyamides (poly(amino acids)) phosphorous-based polymers (polyphosphate) poly(cyano acrylates) polyurethanes polyortho esters and polyacetals. Extreme attention has to be paid to the biodegradability and biocompatibility of the polymers. It is essential that polymers used for medical applications are not detrimental for the tissue or cells and that they can be easily decomposed into simple harmless molecules and eliminated by the human body [ 18-22]. 

Sugar esters are also found widely in nature. Phosphoric acid esters are important intermediary products of metabolism, while sulfuric acid esters are constituents of some polysaccharides. Examples of organic acid esters are vacciniin in blueberry (6-benzoyl-D-glucose) and the tannintype compound, corilagin (1,3,6-trigalloyl-D-glucose) ... 

Polysaccharides with strongly acidic residues, present as esters along the polymer chains (sulfuric, phosphoric acids, as in furcellaran, carrageenan or modified starch), are also very soluble in water and form highly viscous solutions. Unlike polysaccharides with carboxyl groups, in strongly acidic media these solutions are distinctly stable. 

Nearly all macromolecular natural products are combinations of smaller compounds. Molecular weights of monomeric compounds rarely exceed 600. Polysaccharides (starch, cellulose) are linke d by hemiacetal bonds proteins, by acid-amide bonds, also called peptide bonds (see Table III). Ester linkages are found in fats and lipids (not of very high molecular weights) as well as in the macro-molecular nucleic acids, which are phosphoric acid esters. 

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