Synthesis of 5′-functionalized nucleosides: S-Adenosylhomocysteine analogues with the carbon-5′ and sulfur atoms replaced by a vinyl or halovinyl unit

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Adenosine and uridine analogues functionalized with alkenyl or fluoroalkenyl chain at C5′ were prepared employing cross-metathesis, Negishi couplings, and Wittig reactions. Metathesis of the protected 5′-deoxy-5′-methyleneadenosine or uridine analogues with six-carbon amino acids (homoallylglycines) in the presence of Grubbs catalysts gave nucleoside analogues with the C5′–C6′ double bond. Alternatively, the Pd-catalyzed cross-coupling between the protected 5′-deoxy-5′-(iodomethylene) nucleosides and suitable alkylzinc bromides also provided analogues with alkenyl unit. Stereoselective Pd-catalyzed monoalkylation of 5′-(bromofluoromethylene)-5′-deoxyadenosine with alkylzinc bromides afforded adenosylhomocysteine analogues with a 6′-(fluoro)vinyl motif. The vinylic adenine nucleosides produced time-dependent inactivation of the S-adenosyl- l-homocysteine hydrolases.