Studies on Transfer Ribonucleic Acid and Related Compounds. XIII. Synthesis of Trinucleoside Diphosphates, A-U-A and εA-U-A via a Triester Intermediate

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ApUpA (XI) and its 1, N⁶-ethenoadenosine analog, _εApUpA (XII) were synthesized by condensation of the protected mononucleotides, 5'-O-monomethoxytrityl-N, 2'-O-dibenzoyladenosine 3'-phosphate (VIII) or 5'-O-monomethoxytrityl-2'-O-benzoyl-1, N⁶-ethenoadenosine 3'-phosphate (IX) with the triester, 2'-O-benzoyluridylyl-(3'-5')-N, N-2', -3'-O-tetrabenzoyladenosine (VI), in yields of 29% and 24%, respectively. The triester (VI) was prepared by two appraoches. Best results were obtained by condensation of 5'-O-monomethoxytrityl-2'-O-benzoyluridine 3'-phosphate (I) with N, N-2', 3'-O-tetrabenzoyladenosine (III) in the presence of 2, 4, 6-triisopropylbenzenesulfonyl chloride and subsequent treatment with β-cyanoethanol. Deprotected trinucleoside diphosphates, ApUpA (XI) and _εApUpA (XII), were isolated by chromatography on diethylaminoethyl cellulose and the fluorescence quenching of _εApUpA was observed by measurement of the spectra before and after enzymatic digestion of the trimer.