Investigation of activation of phosphate groups in mono- and oligonucleotides with mesitoyl chloride

It has been demonstrated with the use of 31P NMR pulsed spectroscopy that the reaction of mesitoyl chloride (MsCOCl) both with terminal and internucleotide phosphate groups pA, d(MeOTr)TpT and dpTpT (Ac) proceeds in a quantitative fashion within less than 2 min at 0 degrees C with the respective mixed anhydrides being thereby formed. The anhydrides of phosphomonoesters are resistant, unlike those of phosphodiesters which may be readily split by water, alcohol or amine without the internucleotide bonds being broken. Treatment of poly(U) with an excess of MsCOCl leads to rapid cyclization followed by formation of phosphotriesters. A comparatively easy hydrolysis leads to partial cleavage and isomerization of internucleotide bonds. A similar treatment of UpC showed that about 20% of the internucleotide bonds are cleaved, the remaining UpC being a mixture of approximately equal amounts of 3'-5'- and 2'-5'-isomers.