Crystal and molecular structure of bicuculline

The crystal and molecular structure of the phthalide isoquinoline alkaloid bicuculline, C₂₀H₁₇NO₆, has been determined by X-ray diffraction methods. The compound crystallizes in the orthorhombic space groupP2₁2₁2₁ (No. 19) witha = 14·49,b = 10·90 andc = 10·43 Å. The atomic parameters were refined by least squares to give a conventionalR-factor of 0·0437 for 1557 symmetry independent reflections.The bicuculline molecule consists of two approximate planes of atoms with a dihedral angle of 14·3 ° between them. The two planes are joined by the bond. The torsion angle is 164·1 ° in the crystal, but in the liquid state there would be partial free rotation about the bond.The structure of bicuculline is of current pharmacological interest as it is a relatively selective antagonist of -aminobutyric acid at various sites of the nervous system.