Studies on 2′-α-C-carboxyalkyl nucleosides and their application to a stereocontrolled nucleobase exchange process

Abstract

The ability of 2′-α-C-carboxyalkyl nucleosides to undergo an unusual two-step stereocontrolled nucleobase exchange process has been investigated. Upon silylation a protected 2′-deoxy-2′-α-C-(carboxymethyl)uridine derivative can undergo intramolecular displacement of the uracil base, by the 2′-carboxylic acid group, to form a pentofuranosyl γ-lactone. Under identical conditions the homologous 2′-deoxy-2′-α-C-(carboxyethyl)uridine derivative does not yield the corresponding δ-lactone, but undergoes elimination of uracil to give the corresponding glycal. The pentofuranosyl γ-lactone is a good substrate for nucleoside synthesis by the Vorbrüggen procedures and undergoes completely stereoselective ring opening with either pyrimidine or purine silylated nucleobases to give novel 2′-C-carboxymethyl β-nucleosides in moderate to high yield.