PARTIAL PROTECTION OF CARBOHYDRATE-DERIVATIVES .3. REGIOSELECTIVE 2'-O-DEACYLATION OF FULLY ACYLATED PURINE AND PYRIMIDINE RIBONUCLEOSIDES WITH HYDRAZINE HYDRATE

In 1:4 (v/v) glacial acetic acid-pyridine, partial O-deacylation of fully acylated purine and pyrimidine ribonucleosides upon hydrazinolysis was found to be induced regioselectively in respect to the three ester functions at the 2′-position to give the corresponding 2′-OH derivatives in good yields; e.g. 3′,5′-di-O-benzoyladenosine (70% yield), N 2,3′,5′-tribenzoylguanosine (63% yield), 3′,5′-di-O-benzoylinosine (52% yield), N2-benzoyl- 3′,5′-di-O-acetylguanosine (42% yield), and 3′,5′-di-O- benzoyluridine (39% yield) were isolated. Moreover, 5′-O- acylribonucleosides were prepared in quantitative yields by use of an excess of hydrazine hydrate in 1 :1 (v/v) chloroformmethanol and in pyridine. Hydrazinolysis of 3′,5′-di-O-acetyl-2′-deoxyribonucleosides in pyridine was found to give both 5′, and 3′-O-acetyl-2′- deoxyribonucleosides in comparable amounts (80 - 90% total yields). Furthermore, hydrazinolysis of N6,2′,5′-triacetyl-3′-O- methyladenosine and N6,3′,5′-triacety-2′-O- methyladenosine demonstrated that the 2′-O-acetyl group is far more labile toward the nucleophile than the 3′-O-acetyl group. The possible factors involved in the regioselectivity of hydrazinolysis are discussed.