Syntheses and Properties of Oligothymidylate Analogs Containing Stereoregulated Phosphoromorpholidate and Phosphodiester Linkages in an Alternating Manner

Abstract
Syntheses and some properties of undecathymidylate analogs containing stereoregulated phosphoromorpholidate and phosphodiester linkages in an alternating manner are described. These analogs were easily obtained by the phosphorobisamidite approach starting from pre-separated diastereomerically pure dithymidine phosphoromorpholidate derivatives. Both isomers were found to be high resistant to nucleases, in comparison with natural oligothymidylate; the phosphodiester linkages except 3’-end in the isomers were not cleaved by SI nuclease and both isomers were very slowly degraded by phosphodiesterase I and micrococcal nuclease. The rate of each degradation was dependent on the configuration of phosphoromorpholidate linkage in each isomer. The UV and CD spectral studies show that one of the isomer can interact with poly(dA) to give B-type duplex possessing the same thermal stability as natural oligothymidylate-poly(dA) duplex and the other isomer does not interact with poly(dA) under the comparable conditions.

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