Phosphoric acid esters preferential

Aminophosphatides—Monodealkylation of phosphoric acid esters s. 19, 26 Selective removal from peptide hy dr azides—Preferential removal s. 76, 31 Alkoxylamines from N-acylalkoxylamines ONHAc ONHg... 

Phosphatidylcholine can be completely hydrolysed with aqueous acid to produce fatty acids, glycerol, phosphoric acid and choline. With alkali, the fatty esters are preferentially hydrolysed, leaving the glycero-phosphoryl-cholines, which can in turn hydrolyse slowly into glycerophosphoric acid and choline. Enzymatic hydrolysis occurs selectively at different ester sites by several phospholipases to produce a range of products. Phospholipases A1 and A2 are obtained commercially from snake venom. They hydrolyse the fatty acid at the -1 and sn-2 positions respectively, to produce lysophosphatidyl-choline. Phospholipase C catalyses the hydrolysis of the phosphate moiety to give 1,2-diacylglycerols and phosphorylcholine. Phospholipase D found in plant tissues mainly catalyses hydrolysis of the phosphate ester to produce choline and phosphatidic acids (1). 

Analysis of PPA demonstrates that it is composed mainly of phosphoric acid tetramers (from hydrolysis of P4O10), as illustrated in Scheme 18.11. During the initial stage of quinacridone synthesis, reaction with a terephthalic acid 17 results in the formation of phosphate esters. A bis-diphosphate (bis-pyrophosphate) ester species 23 is displayed in the reaction scheme although a variety of combinations of mono- to triphosphate esters could and probably do form and probably equilibrate with each other also, in the hot acid. However, due to the symmetry of the tetrameric phosphoric acid and the known nucleofugic propensity of a diphosphate moiety, bis-diphosphate esters such as 23 probably form preferentially as reactive intermediates and by analogy, diphosphate esters would be expected to significantly facilitate the cycUzation process. 

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