Phosphate ester, conformational studies

Reactions of Phosphoric Acid and its Derivatives.—Theoretical studies on the conformational properties of cyclic and acyclic phosphate esters, including calculations of angle and torsional strain,66 and on the reactivity of monomeric metaphosphates,67 have appeared. 

The structures of 1,3,2-dioxaphosphinanes of biochemical significance to have been solved by x-ray crystallography are numerous the phenyl ester of thymidine 3, 5 -cyclic phosphate is an example <75PNA(72)1335, 87JA4058>. In the 1,3,5-dioxaphosphinane series, conformational studies by NMR have been supported by x-ray crystal structures <87IZV418>. 

A conformational study of nucleic acid phosphate esters has been carried out using n.m.r. and the temperature-dependent chemical shifts used to give information about the geometry of the phosphodiester linkage. Compounds studied were 3 - and 5-O-methyl phosphates of uridine and adenosine, and the 3-0-methyl phosphate of 6-A-dimethyladenosine. It has been reported that the n.m.r. of myo-inositol hexakisphosphate has four resonances that shift and broaden as a function of pH. ° Reference to the use of P n.m.r. in the configurational determination of cyanomethyl-branched phosphonates is made in Chapter 16. 

There have appeared several studies on the conformation of acyclic phos-phonic and phosphinic esters and some calculations on the equilibrium conformation of a series of enol phosphates have been reported.Crystal structure determinations on the very reactive cyclic phosphate (1 R = MeO) have shown that the five-membered ring is almost planar and that the carbonyl bond is short. 

C—0 and P—0 ester bonds Phosphate diester is tetrahedral and shows antiperi-planar conformations for the C5 —05 bond. X-ray structural studies of tRNA and DNA oligomers suggest that usually H4 —C4 —C5 —05 — P adopts an extended W-conformation in these structures. 

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