Polynucleotides. XXVI. Synthesis of an AUG Analog, 8, 2-Anhydro-8-oxy-9-β-D-arabinofuranosyladenine Phosphoryl-(3'-5')-uridylyl-(3'-5')-guanosine

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A triplet AUG analog containing 8, 2'-O-cycloadenosine in the first position was synthesized. Starting from 2'-O-(2, 4, 6-triisopropylbenzenesulfonyl)-8-bromoadenosine (I), 5'-monomethoxytrityl-8, 2'-O-cycloadenosine (IV) was synthesized via 8-oxy derivative (II) by the successive treatment with sodium acetate, monomethoxytrityl chloride and methanolic ammonia. Phosphorylation of compound IV with cyanoethyl phosphate and dicyclohexylcarbodiimide (DCC) at 18-20° for 5 days gave only 3'-cyanoethylphosphate (V) quantitatively. Treatment of V with methanolic ammonia gave 3'-phosphate (VI) in a relatively low yield with concomitant formation of 2', 3'-cyclic phosphate (VII). Compound VI was then condensed with 2'-O-benzoyluridylyl-(3'-5')-N², 2', 3'-triisobutyrylguanosine (X) using DCC and after purification on a column of diethylaminoethyl (DEAE)-cellulose, 8, 2'-O-cycloadenylyl-(3'-5')-guanosine (XI) was obtained in a yield of 4.1%. Compound XI showed hypochromicity of 7.3% at 257 nm and circular dichroism (CD) spectra taken at 0° and 20° revealed that this trinucleotide exists in a rather freely rotatable, unstacked form both at these temperatures.