The application of levulinic acid as protective group to the synthesis of tetradecaribonucleotide U‐A‐U‐A‐U‐A‐U‐A‐U‐A‐U‐A‐U‐A <i>via</i> the modified phosphotriester method

Abstract

Abstract Acylation on the 5î‐position of 2î‐ O ‐methoxytetrahydropyranyl ribonucleosides la (B=U) and 2a (B=A an ) with levulinic acid, followed by phosphorylation of the 3î‐hydroxy function with the monofunctional phosphorylating agent 2,2,2‐trichloroethyl 2‐chlorophenyl phosphoro‐chloridate (3), afforded the fully‐protected mononucleotides 4a and 5a , respectively, in reasonable yields. The latter compounds were key‐intermediates in the synthesis of fully‐protected tetradecaribonucleotide 15a . The preparation of tetradecamer 15a was achieved by using two specific deblocking procedures, i.e. (a) zinc in pyridine/2,4,6‐triisopropylbenzenesulfonic acid to cleave the 2,2,2‐trichloroethyl group and (b) hydrazine in pyridine/acetic acid for the rapid and selective removal of the levulinyl group. Deblocking of the 2‐chlorophenyl groups from 15a was successfully accomplished by the action of fluoride ion. Attention is directed to anomalous reactions occurring with the use of this deblocking reagent.