Phosphoramidates 5 -pyrophosphates

Compound (1) phosphorylates phosphate monoesters and alcohols, although with the latter a considerable excess of alcohol is necessary to obtain satisfactory yields. In the absence of mercuric ions the milder phosphorylating species (3) can be isolated which converts monoalkyl phosphates to pyrophosphate diesters in good yield but does not react appreciably with alcohols unless catalytic amounts of boron trifluoride are added. Amine salts of (3) are converted to phosphoramidates on heating. In the presence of silver ions, O-esters of thiophosphoric acid behave as phosphorylating agents and a very mild and convenient procedure suitable for preparing labile unsymmetrical pyrophosphate diesters, such as the... 

The reaction of 151 with methanol to give dimethyl phosphate (154) or with N-methylaniline to form the phosphoramidate 155 and (presumably) the pyrophosphate 156 complies with expectations. The formation of dimethyl phosphate does not constitute, however, reliable evidence for the formation of intermediate 151 since methanol can also react with polymeric metaphosphates to give dimethyl phosphate. On the other hand, reaction of polyphosphates with N-methylaniline to give 156 can be ruled out (control experiments). The formation of 156 might encourage speculations whether the reaction with N,N-diethylaniline might involve initial preferential reaction of monomeric methyl metaphosphate via interaction with the nitrogen lone pair to form a phosphoric ester amide which is cleaved to phosphates or pyrophosphates on subsequent work-up (water, methanol). Such a reaction route would at least explain the low extent of electrophilic aromatic substitution by methyl metaphosphate. 

The first application of this reaction for the synthesis of sugar nucleotides was reported in 1958, when Moffatt and Khorana269 prepared uridine 5 -(a-D-glucopyranosyl pyrophosphate) (5) in 59% yield from uridine 5 -phosphoramidate (58). Other examples of similar... 

In all of the foregoing examples, an activated derivative of the nucleotide has been employed for generating the pyrophosphate link. An attempt to use an activated glycosyl phosphate failed 311 the only product identified from the reaction between /3-D-glucopyranosyl phosphoramidate (68) and uridine 5 -phosphate was the cyclic phosphate 69. The ease of participation of the sterically accessible, C-2 hydroxyl group probably accounts for this result. The usual procedure... 

Sodium phosphoramidate, Na2P03NH2, 6 100, 101 Sodium phosphorothioate, Na3-P03S, 6 102 12-hydrate, 5 103 Sodium pyrophosphates, 3 98 Na2H2P2C>7, 3 99 Na4P2C>7, 3 100 Sodium pyrosullite, 2 162, 164 and its 7-hydrate, 2 165 Sodium rare earth sulfates, 2 42, 46... 

Extensive work has been reported on the chemistry of polyphosphates, in particular that of dinucleoside and sugar nucleoside pyrophosphates. This reflects the reliability and flexibility of the phosphoramidate methods which have been developed over the past few years. Similarly, a wide range of oligonucleotide building blocks, incorporating extensive structural modifications when compared to the natural nucleoside structures, have been described. 

Treatment of thymidine 5 -phosphorodiamidate (54) with pyrophosphate in anhydrous DMF leads to the formation of P -(thymidine-5 )-P -aminotriphosphate (55) in good yield. The compound is sufficiently stable to be purified on DEAE-Sephadex at low temperature. In acid, conversion into TTP is quantitative, but in ammonia, thymidine-5 -phosphoramidate and pyrophosphate are formed. Treatment with alkaline phosphatase cleaves (55) to the phosphoramidate. Nucleophilic attack takes place very easily in anhydrous DMF at ambient temperature, (55) is in equilibrium with (56) and pyrophosphate. 

Nucleoside S -phosphoramidates have proved to be useful intermediates in the synthesis of nucleoside 5 -pyrophosphates and nucleotide coenzymes. Nucleoside phosphoramidates may also be prepared by treatment of a nucleoside 5 -phosphate with ammonia in the presence of N, IV -dioyclohexylcarbodiimide [R. W. Chambers and J. G. Moffatt, J. Am. Chem. Soc., 80, 3752 (1958)]. 

The chemical synthesis of uridine 5-(a-D-glucopyranosyl pyrophosphate) has been effected by condensing a-n-glucopyranosyl phosphate with uridine 5-phosphate in the presence of dicyclohexylcarbodiimide. The yield of glycosyl nucleotide in this reaction is very low, primarily because dicyclohexylcarbodiimide promotes the formation of n-glucose cyclic 1,2-phosphate in preference to the formation of the pyrophosphate bond. In an improved synthetic method, the nucleotide is first converted to a phosphoramidate (5) or phosphoromorpholidate (6), by condensation in the presence of dicyclohexylcarbodiimide with ammonia or morpholine, respectively. 

The D Souza and Bender system shows many of these features. Systems that induce bond formation require the presence of several binding and reactive groups. The catalytic molecule should act as a co-receptor bringing together reactant, substrate and intermediate complex. As an example, Hisselni and Lehnl l demonstrated pyrophosphate formation from the intermediate phosphoramidate formed by phosphorylation of the macrocycle by ATP. In a second reaction step, the phosphoramidate reacts with a phosphate group to form pyrophosphate (see Fig. 7.10). 

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