In order to study adenine-amide interactions, 3-(adenin-9-yl)propionamide has been synthesized and its crystal structure examined. The crystals are monoclinic, the space group being P21/a, with unit-cell dimensions of a=25.668 (1), b=8.025 (1), c=4.684 (1) Å, β=103.54 (1)°, and Z=4. The adenine bases are linked along the two-fold screw axis through the hydrogen bonds, N(6)H···N(1) and N(6)H···N(7). The amide group is hydrogen-bonded to N(3) of adjacent adenine moiety, the distance NH···N(3) being 3.055 Å. The model fitting by computer graphics indicates that this binding scheme could be an elementary interaction pattern between the amide group in protein and adenine in the minor groove of double helical DNA.

As a ternary interaction model between adenine:thymine base pair and carbamoyl group, 3-(adenin-9-yl)-propionamide: 1-methylthymine complex was prepared and its crystal structure was examined. The crystal exhibits a disordered structure, and the structure unit is a monoclinic cell with dimensions a=11.368(1), b=6.909(1), c=12.708(2) Å, and β=114.49(1)°. The space group is P21 and the unit cell contains two complexes and four water molecules. The base pairing pattern between adenine and thymine is the Hoogsteen type. The carbamoyl group is hydrogen-bonded to N(A1) of adenine in this base pair, the distance NH···N(A1) being 2.94(2) Å. With two kinds of hydrogen bonds of the carbamoyl group, NH···N(A1) above-mentioned and NH···O(carbamoyl), the 3-(adenin-9-yl)propionamide molecules form a sheet extending perpendicular to the c axis; the base-paired thymine molecules extrude alternately from the sheet. Diffused spots along c* with half integers of l can be interpreted as a stacking disorder of the sheets.

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3-(Adenin-9-yl)-N-(2-succinimidyl)propionamide has been synthesized as a model for studying the interaction between cyclic ureide and adenine, and its crystal structure examined. The crystals are monoclinic, the space group P21/c, with unit-cell dimensions of a=10.861(1), b=12.766(1), c=9.753(1) Å, β=91.10(1)°, and Z=4. The ureide moiety is hydrogen bonded to adenine with NH···N(1) (2.903(3) Å) and O···HN(6) (2.955(3) Å). A comparison of the hydrogen bonding patterns of the related compounds with adenine suggests that cyclic ureide anticonvulsant drugs possess the capability of interacting with N(1) and N(6) sites of adenine.