Oxygen Chiral Phosphate in Undylyl(3'→5')adenosine by Oxidation of a Phosphite Intermediate: Synthesis and Absolute Configuration

Coupling of 2’,5′-silylated uridine and 2’,3′-silylated N6-benzoyladenosine with dichloromethoxyphosphine furnished dinucleoside monophosphite triesters. Oxidation of these intermediates with [17O,18O]H2O and iodine afforded the diastereoisomeric phosphate triesters of fully protected [170, 18O]UpA having the oxygen labels in the P=0 group. The diastereoisomeric mixture of major and minor components was separated by column chromatography. Stereospecific cleavage of the phosphate protecting group by thiophenolate followed by desilylation with (Bu)4NF yielded the oxygen chiral isotopomers of [17O,18O]UpA. The incorporation of 17O was demonstrated by 17O NMR spectroscopy and of 18O by 31P NMR spectroscopy. Hydrolysis of the major isotopomer with nuclease P1 in [17O, 18O]H2O with inversion of configuration at phosphorus yielded [16O,17O,18O] AMP. This was converted into the isotopomers of the respective cyclic 3’,5′-phosphate with inversion of configuration. Methylation of the latter followed by 31P NMR spectroscopy established the absolute isotopic configuration of the [16O,17O,18O] AMP as Sp. The absolute configurations of the diastereoisomeric triesters from the phosphite oxidation are therefore assigned as Sp for the major isomer and Rp for the minor isomer. Consequently, the resulting deprotected isotopomers of [17O, 18O]UpA have the opposite Rp and Sp configurations, respectively. Methylation of (Rp)-[17O,18O]UpA gave two diastereoisomeric triesters whose absolute configurations were established by inspection of the 18O isotope shifts on phosphorus in the 31P NMR spectrum. An unknown absolute isotopic configuration of [18O]UpA can now be determined by methylation and subsequent 31P NMR spectroscopy. © 1983, American Chemical Society. All rights reserved.