Phosphoric esters protection

Protection of phosphoric esters is particularly required for nucleotide synthesis, where some interesting applications of photosensitive groups. 

The photosolvolysis of 3-nitrophenyl esters is the first example of the use of a light-sensitive protecting-group that has appeared in the literature. 3-Nitrophenyl and the more-sensitive 3,5-dinitrophenyl phosphoric esters undergo photohydrolysis (mercury lamp) to a phosphoric derivative and the corresponding nitrophenol an example of a synthetic application is presented in Scheme 30. 

Organophosphate inhibitors include aminotrimethylenephosphonate (AMP), hydroxyethylidene disphosphonate (HEDP), carboxylates and phosphate esters. They are often used in conjunction with other inhibitors such as zinc. Phosphorates generate protective films are susceptible to rupture, however, and pretreatment of the surfaces is often necessary. Organophosphate inhibitors work best in elevated pH environments, which reduces the corrosivity of the cooling wastes. 

Protective group for nucleosides. Stepwise synthesis of oligonucleotides utilizing 2-cyanoethyl phosphate (1, 172-173) requires protection of the 3 -hydroxyl group which can be cleaved under essentially neutral conditions, since a methoxy-trityl ether is sensitive to acid and a /3-cyanoethyl phosphoric ester is sensitive to alkali. The /3-benzoylpropionyl group meets these requirements, since it is quantitatively cleaved by dilute solutions of hydrazine hydrate in pyridine-acetic acid. The esters are prepared by condensation with DCC (dicyclohexylcarbodiimide). Definitive paper R. L. Letsinger and P. S. Miller, Am. Soc., 91, 3356 (1969)... 

XPS was also used to evaluated the surface composition of limestone after treatment with a protective material of a fluorinated phosphoric ester, by XPS [46]. Torrisi used XPS to study commercial fluorinated compounds as a protection of calcarenite surfaces, before and after ageing in a climatic chamber simulating exposure to solar radiation, [47]. 

Lipid A, its relatives lipid X and Y, and their analogues are esterified 2-amlno-2-deoxy-D-glucopyranose derivatives, as exemplified by the recently synthesized Proteus mirabilis lipid A (83). Novel synthetic aspects generally involve protecting group manipulations and carboxylic and phosphoric ester forming procedures further details may be found in Chapter 7. The majority of publications have come from the groups of Achlwa (mostly full... 

O-isopropylidene derivative (10) was then phosphorylated with phosphorous oxychloride to form the phosphate ester (11) from which the protecting groups were removed by mild acid hydrolysis. The 3-phos-phate (15) was obtained by phosphorylating the 4,6-benzylidene derivative (13) of the same glycoside with phosphorus oxychloride, followed by hydrolytic removal of the protecting groups, from the ester (14) thus obtained. 

Treating petroleum oils with 3-5% calcium alkyl salicylate and 0.5-3% triethanolamine salts of phosphoric acid esters and ethoxylated dodecyl alcohol increases oxidation-thermal stability at 180-200°C in the manufacture of oil for metal parts quenching. The agent provides also short-term anticorrosion protection of the hardened articles [261]. Phosphoric acid salt alkyl esters are used in anticorrosives and aqueous dispersions in waterborne polyester coatings for metals [244]. 

Benzyl esters of phosphoric acid have been employed also with success in organic synthesis. Usually palladium catalysts are used to remove the benzyl protecting group (Scheme 4.50). 

Both the benzyl esters of carboxyl and phosphoric acid groups and benzy-loxymethyl protecting groups were removed in a one-step deprotection on 10% Pd/C in THF-water at 50 psi H2 for 12 hours (Scheme 4.51).235... 

The Schneider group independently reported an asymmetric vinylogous Mannich reaction (Scheme 27) [47]. Addition of silyl dienolates 73 to A-PMP-protected imines 74 was promoted by phosphoric acid (R)-3g (5 mol%, R = Mes) with mesityl substituents to afford tra i -a,p-nnsatnrated 8-amino esters 75 in high yields (66-94%) together with good enantioselectivities (80-92% ee). 

In 2008, the Rueping group reported the addition of nitroalkanes 78 to A-PMP-protected a-imino esters 79 in the presence of chiral phosphoric acid (R)-14r (10 mol%, R = SiPhj) (Scheme 29) [51]. This transformation provided P-nitro-a-amino esters 80 in good yields (57-93%), anrt-diastereoselectivities (2 1-13 1) and enan-tioselectivities (84-92% ee). 

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