Crystal Structures of Baclofen Analogs: 3-Thienyl- and 3-Furylaminobutyric Acids

X-ray crystal structures of 4-amino-3-(2-thienyl) butyric acid (compound1), 4-amino-3-(4-bromo-2-thienyl) butyric acid (compound2), and 4-amino-3-(5-methyl-2-furyl) butyric acid (compound3) are reported. Space groups and unit/cell parameters are: compound1, monoclinic,P21 c,a=13.288(3),b=5.231(1),c=12.388(2)Å,β=92.3(1)°; compound2, monoclinic,P21/c,a=12.610(7),b=5.156(1),c=15.814(8)Å,β=101.8(1)°; compound3, orthorhombic, Pccn,a=11.461(1),b=25.284(2),c=6.977(1)Å. FinalR indices are: compound1, 0.057; compound2, 0.069; compound3, 0.060. Conformations of their γ-aminobutyric chains are compared with the one of γ-amino-β-(p-chlorophenyl)-butyric acid (baclofen, compound4). Two different types of conformations are observed, i.e., conformations (i) with folding (compound3) or (ii) without folding (compounds1,2, and4) of the ammonium group toward the heteroaromatic or aromatic ring. However, distances between ionized groups are constant.