SUBSTITUTED PHOSPHATES

Phosphate X=H Phosphite Hypophosphite Phosphine oxide Phosphonium  

Substituted tetrahedral phosphates based on a single P atom can be represented as in (5.208), where X can be H, halogen, NH2, alkyl, aryl, etc. Successive replacement of O by X results in a progressive 

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Phosphoric acid chloride and thiophosphoric acid chloride pyrididium betaines (I) which are easily prepared by reacting P401Qt P OgS. and P4S1Q, respectively, with phosphorus oxychldride or phdspnorus thio-chloride in the presence of pyridine (1.), are of interest for the synthesis of substituted phosphates and thiophosphates. 

To verify this idea the methyl substituted phosphate complex 62 was synthesized and separated into its optical antipodes. The reaction with protons was not regiospecific but to a certain extent stereoselective, and the isolation of optically active phosphorane 63 was greatly helped by fortunate incursion of a spontaneous racemate separation 73>. 

Esterification with diazomethane [590—593] is another possible derivatization procedure for substituted phosphates. However, it has been used for only a limited number of substrates. Some workers [592] obtained very good quantitative yields with it in comparison with other methods. 

A large number of xenobiotics, such as esters, amides, or substituted phosphates that include ester-type bonds, are susceptible to hydrolysis. Hydrolytic reactions are the only phase I reactions that do not utilize energy. Numerous hydrolases are found in blood plasma, liver, intestinal muscosa, kidney, muscle, and nervous tissue. Hydrolases are present in both soluble and microsomal fractions. The general reactions are shown in Figure 10.10A. 

Just as the three-dimensional type of structure of SiOz occurs in the felspars as a consequence of isomorphous substitution, phosphates such as A1P04 and BPO4, in which A1 and B both have a coordination number four, also have structures which correspond to those of the SiOa modifications, quartz and cristo-balite, respectively. 

In addition to the above well-defined silicophosphates, there have been many attempts to substitute phosphate anions into fonr-coimected siUcate zeolites (see Zeolites). Snbstitntion of 5 25% phosphate into zeolites such as Faujasite have been reported, but these materials are less well-characterized than the aluminophosphates and silicon aluminophosphates described below. 

The possibility of electron donation by cyclopropane to an electron-deficient phosphorous in a highly substituted phosphate for which the X-ray structure is available unfortunately cannot be properly assessed because the heavy substitution on the ring obscures the interpretation of the observed bond lengths and angles . ... 

The mechanism of action of oxime reactivation involves transfer of the substituted phosphate or phosphonate residue from the catalytic site of the... 

Gaydou, E.M., Freze, R., and Buono, G., Enol phosphates. Part 5. Synthesis and physical properties of substituted phosphates. Bull. Soc. Chim. Fr, 2279, 1973. 

E Phosphodiester- ases Phosphomonoester transfer from a phosphodiester other than polynudeotide to water as an acceptor molecule. (Phospho-diesters are deaved hydrolytically). 2.7.8. Transferases for other substituted phosphate groups 3.1.4. Phosphoric diester hydrolases... 

Imidodiphosphates are also potential substrates for phosphoryl hydrolyzing enzymes (see Table 13-8, entry 7). They have been used less often than the S-substituted phosphate analogs. 

An ester of glycerol containing two fatty acids consists of a long nonpolar "tail" and a polar substituted-phosphate "head"... 

Phospholipids are similar in stmcture to fats in that they are esters of glycerol. Unlike fats, however, they contain only two fatty acids. The third group bound to glycerol is a phosphate group, which gives phospholipids two distinct parts the long nonpolar "tail" and the polar substituted-phosphate "head" (see Figure 21.21). 

Lecithin, a phospholipid, with its long nonpolar tails and polar substituted-phosphate head... 

Many pesticides have ester bonds, amide bonds, or substituted phosphate ester groups that are susceptible to hydrolysis by esterases. Enzymes with carboxylesterase (CarbE) and amidase activities are found in both microsomal and soluble fractions from a variety of tissues. Although functionally ester and amide groups are different, no CarbE has been found that does not have hydrolytic activity toward the corresponding amide and vice versa. 

Figure 16.3 Schematic representation of a lateral pressure profile in a vesicular bilayer. Only one monolayer is shown here, the same profile applies for the other monolayer. The lateral pressure n depends on the depth (Z) in the monolayer. From M. Kuiper, Azobenzene-substituted Phosphate Amphiphiles Effect of Ught-induced trans-cis Isomerisation on Vesicular Properties and the Channel Protein MscL, Ph. D. Thesis, University of Groningen, p 2, 2005...

In addition Cobalt substituted Phosphates were also characterized using P MAS NMR. The Ip chemical shift was not shown to depend critically on the nature of the adjacent tetrahedron. Yet the chemical shift anisotropy is very strongly dependent on the adjacent tetrahedron. Adjacent paramagnetic Co resulted in a very strong anisotropy of the screening tensor reflected by an extended pattern of spinning side bands which could not be removed in spite of fast spinning (33). 

If only P-0 linkages are present, the compounds can be termed normal phosphates. If, on the other hand, some of the oxygens are replaced by other atoms or groups, the compounds will be termed substituted phosphates. When X = H, the compounds are more widely known as phosphites (5.4a) or hypophosphites (5.4b) and these are dealt with in Section 5.5. When X = CR3 or NR2, the substituted phosphates are also carbophosphorus compounds (Chapter 6) or azaphosphorus compounds (Chapter 7), respectively. Substituted phosphates which contain a single P=0 linkage (5.4c) are referred to as phosphoryl compounds. 

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