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  • 1
    ISSN: 1434-193X
    Keywords: Nucleotides ; Thiophosphates ; Hydrolyses ; Reaction mechanisms ; Kinetics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrolysis of the cis-methyl ester of 3′-deoxy-3′-thiothymidine 3′-S,5′-O-cyclic(phosphorothiolate) (1a) has been followed by HPLC and MS. At pH 〈 2 hydrolysis of the thiophosphate triester moiety is acid-catalyzed (first order), while between pH = 2 and 5 the reaction is pH-independent and at pH 〉 5 first order in hydroxide ion. The uncatalyzed and acid-catalyzed reactions yield two thiophosphate diesters, the 3′-S,5′-O-cyclic phosphorothiolate 2 and 3′-S-phosphorothiolate methyl ester 3, in a 9:1 and 1:3 molar ratio, respectively. The hydroxide ion catalyzed reaction gives the endocyclic P-O and P-S bond-cleavage products (3 and 4, respectively) in a 1:2 molar ratio. The pH-independent reaction is suggested to take place by attack of a water molecule on the carbon atom and concomitant C-O bond rupture, whereas the alkaline and acidic reactions involve attack of the nucleophile on the phosphorus atom and formation of a pseudorotating thiophosphorane intermediate. Under acidic conditions, cleavage of the N-glycosidic linkage competes with the phosphoester hydrolysis, corresponding to 20% of the hydrolysis products at pH 〈 1.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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