Adenosine Receptor Agonists. X-Ray Crystal Structure of Neca 1-(6-Amino-9<u>H</u>-Purin-9-Yl)-1-Deoxy-N-Ethyl-β-D-Ribofuranuronamide

The single crystal x-ray structure of NECA (1-(6-amino-9H-pu-rin-9-yl)-1-deoxy-N-ethyl-β-D-ribofuranuronamide), a 5′-modified adenosine analogue, is reported. Crystallized from methanol as the monohydrate, NECA exists in a syn conformation (sugar syn to purine) in the solid state, consistent with both solution measurements and theoretical calculations. The biological profile of NECA may result from this conformational preference.