Tris trimetaphosphate

Although reasonably stable at room temperature under neutral conditions, tri- and tetrametaphosphate ions readily hydrolyze in strongly acidic or basic solution via polyphosphate intermediates. The hydrolysis is first-order under constant pH. Small cycHc phosphates, in particular trimetaphosphate, undergo hydrolysis via nucleophilic attack by hydroxide ion to yield tripolyphosphate. The ring strain also makes these stmctures susceptible to nucleophilic ring opening by other nucleophiles. 

On use of N,N -dicyclohexylcarbodiimide instead of sulfonyl chlorides as condensation reagent in oligonucleotide synthesis, then the pyro-, tri- and tetraphosphate stages are again involved 124). The metaphosphate 183 a is found in small amounts by 3iP-NMR spectroscopy, but again no cyclic trimetaphosphate 184 can be detected, which would also be a possible phosphorylation reagent. 

Selective reaction at the ci.s-2,3-diol grouping of unprotected D-ribonucleosides has occasionally been observed. Treatment of D-ribonucleosides with tris(tetramethylammonium) trimetaphosphate in M sodium hydroxide for 4 days at room temperature led to a mixture of nucleoside 2 - and 3 -phosphates in yields of >70% no 5 -phosphate was detected.213 Reaction of ethyl (trichloromethyl)phos-phonate with nucleosides in N,N-dimethylformamide containing triethylamine, followed by basic hydrolysis of the reaction product, yielded 2 (3 )-phosphates in variable yields.214 The participation of the cis-diol grouping in the reaction was suggested by the failure of thymidine or 2, 3 -0-isopropylideneuridine to undergo reaction. 

Solutions of alkali trimetaphosphates are practically stable under neutral conditions and at 20°C or below. At a lower pH they are hydrolyzed according to a first order law and transformed via tri- and di-phosphates to monophosphates (10, S3, 51, ISO, 238, 244, 393). 

This formula also corresponds with the fact that dissociation is strong in three and weak in two of the five H+ ions in triphosphoric acid (250). The correctness of the structural formula is also supported by the quantitative formation of triphosphate from trimetaphosphate on cleaving the anion ring with strong alkali (90, 311). Final proof for the structure of the tri-... 

The /3-form of the arsenatophosphate and /3-KAs03 contain trimeric anionic rings. This follows from the isomorphism with the low temperature form of K3(P309), which is formed when KH2P04 is treated with a mixture of acetic acid and acetic anhydride 121). It may also be concluded from the observation that in the hydrolysate of /3-arsenatophosphate it is possible to detect, in addition to monoarsenate and a little trimetaphosphate, only mono- and diphosphate, but no tri- or higher polyphosphate 121). The /3-forms of arsenatophosphates contain anions of the types ... 

The oligomerization is presumed to take place by condensation of thymidine-5-tri-phosphate on the free 3 OH of TMP with the release of pyrophosphate. It is not known if the mechanism of synthesis occurs through the cyclic trimetaphosphate intermediate postulated in Khorana s chemical synthesis, but the conditions of synthesis (heating after evaporation at temperatures below 90°C) are not incompatible with such a consideration. 

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