SYNTHESIS AND CHARACTERIZATION OF DODECANUCLEOTIDES CONTAINING THE XHOI RECOGNITION SEQUENCE WITH A PHOSPHOROTHIOATE GROUP AT THE CLEAVAGE SITE

The synthesis and characterization of diastreomeric dodecanucleotides, d[GATC(p(S))TCGAGATC], containing recognition sequence of the XhoI re striction endonuclease with a phosphorothioate internucleotidic linkag e the cleavage site are described. R(p) and S-p form of diastereomeric ally pure dinucleoside phosphorothioates d[C-p(S)T] were presynthesize d and used for the addition to the growing oligonucleotide chain as a block. The stereochemistry of dinucleoside phosphorothioate was assign ed by P-31 NMR spectroscopy, enzyme digestion, and reverse-phase HPLC. XhoI restriction endonuclease cut only R(p) diastereomer d[GATC(p(S)) TCGAGATC]. The rate of hydrolysis is slower than that of the unmodifie d dodecamer d[GATCTCGAGATC]. The phosphorothioate nucleotide is using for determination of the stereochemical course of the XhoI catalyzed r eaction.