2-Pyridyl phosphate, hydrolysis

The spontaneous hydrolysis of 2-pyridyl phosphate (PP) is a good model for the special mechanism (Scheme 15) for the hydrolysis of phosphate monoester monoanions (M ), which are believed to react via an initial proton transfer equilibrium to form the highly reactive species the proton transfer occurring from a hydroxyl group attached... 

The combined kinetic and computational evidence led to the firm conclusion that the spontaneous hydrolysis of di-(2-pyridyl) phosphate (50) supports a single-step, concerted, 5n2(P) mechanism involving the attack of solvent water on phosphorus assisted by intramolecular general base catalysis by a (weakly basic) pyridine nitrogen (Scheme 17). Catalysis was relatively efficient for this mechanism, with an estimated effective molarity of the general base of >15 M, consistent with the absence of catalysis by typical buffers. ... 

The results of quantum theoretical calculations for the hydrolysis reactions, previously studied experimentally, of a series of four triaryl (127 X = H, Cl, SO3 , NOj) and two dialkyl 4-nitrophenyl phosphate triesters (128 R = CHjCFg, Me) together with tris(2-pyridyl) phosphate (129 R = 2-pyridyl) and di-(2-pyridyl) 4-nitrophenyl phosphate (129 R=4-N02-C6H4) showed excellent qualitative agreement with experiment. 

The high rate of spontaneous hydrolysis of tris-2-pyridyl phosphate (96) to the corresponding dietser (97) was explained by the activating elfects of the non-leaving ( spectator ) groups on P-OAr cleavage, and not by intramolecular catalysis as discovered by Kirby and co-workers (Scheme 25). ... 

Dissolve a protein or macromolecule containing primary amines at a concentration of 10 mg/ml in 50 mM sodium phosphate, 0.15 M NaCl, pH 7.2. Other non-amine-containing buffers such as borate, HEPES, and bicarbonate also may be used in this reaction. Avoid sulfhydryl-containing components in the reaction mixture as these will react with the pyridyl disulfide end of SPDP. The effective pH for the NHS ester modification reaction is in the range of 7-9, but hydrolysis will increase at the higher end of this range. 

A quite similar method is employed in the one-carbon chain extension of a 5 -phosphonate isostere of pyridoxal 5 -phosphate (Scheme 5.50) The a , 3-O-isopropylideneisopyridoxal is converted into an oc,P-unsaturated phosphonate in yields up to 65% by condensation with sodium tetraethyl methylenediphosphonate. Selective hydrolysis with 10% HCOjH at reflux gives the key diethyl 2-(3-hydroxy-4-hydroxymethyl-2-methyl-5-pyridyl)vinylphosphonate intermediate in 98% yield. After catalytic hydrogenation of the double bond using 5% Pd/C in EtOH, a comparison of methods for the oxidation of the alcohol has been made, including use of MnOi in water, CrO, Py, and DMSO-DCC. Finally, oxidation with activated MnO2 in CHCl, was found to proceed smoothly to give the diethyl 2-(4-formyl-3-hydroxy-2-methyl-5-pyridyl)cthylphosphonate. ... 

Several studies on intramolecular catalysis of the solvolysis of phosphate esters have been reported. The larger hydrolysis rate of the zwitterion of 8-hydroxyquinoline phosphate (20) compared with that of pyridyl 3-phosphate (21) was attributed, on the basis of the kinetic isotope effect, to intramolecular general acid catalysis. A similar general acid catalysis by the hydroxy-group seems to operate in the (3-hydroxy-2-pyridyl)methyl phosphate dianion (22), which hydrolyses faster than either the monoanion or the neutral molecule. From a study of 4- and 5-substituted derivatives of salicyl phosphate (23) it is suggested that the negligible solvent isotope effect is inconsistent with preliminary proton transfer, and that here also intramolecular general acid catalysis by the... 

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