Isolation and characterization of the diastereoisomers of a series of phosphate-ethylated dinucleoside monophosphates.

Internucleotide phosphate esterification is a common reaction of many potent carcinogenic alkylating agents. It can give rise to two stereochemically distinct molecules about a triesterified phosphorus atom. The eight individual diastereoisomers derived from phosphate ethylation of d-ApT, d-CpT, d-GpT, and d-TpT were prepared from o-chlorophenyl phosphotriester intermediates and isolated by reverse-phase HPLC. Each pair of isomers, together with its parent analog, was examined by variable temperature circular dichroism. The results are interpreted in terms of secondary structure changes from which the absolute configurations of the ethylated phosphate groups can be inferred. These configurational assignments were confirmed by 31P NMR.