Based on finding that AdoHcy hydrolase is able to add enzyme-sequestered water molecule across the 5',6'-double bond of  (halohomovinyl)adenosine analogues A causing covalent binding inhibition, we prepared AdoHcy analogues C with 5',6'-olefin moieties incorporated in place of the sulfur atom.  The analogues C should be substrates for the 'hydrolytic' activity and enzyme-mediated addition of water might occur at C5' or C6' of C.  Cross-metathesis of the suitably protected 5'-deoxy-5'-methyleneadenosine anologue of type B with racemic 2-amino-5-hexenoate D in the presence of Hoveyda-Grubb's catalyst and deprotection afforded C as 5'E isomer of the inseparable mixture of 9'R/S diastereomers in 66%.   Self-metathesis of D was also observed (11%) while self-metathesis of nucleoside substrate B was not noted. Metathesis of chiral homoallylglycine 2S-D produced AdoHcy analogue C (5'E, 9'S).