Quaternary salts of oxo-sparteines: Crystal structure of N(1)-methyl-15-oxosparteine iodide and N(1)-methyl-17-oxosparteine iodide monohydrate

Abstract

The crystal structures of twoN-methiodides, derivatives of the alkaloid sparteine, have been determined by single-crystal X-ray analysis. Diffraction data were collected on a diffractometer using MoKα radiation (λ=0.71073 Å). The finalR factors were 0.043 and 0.031 forN(1)-methyl-15-oxosparteine iodide andN(1)-methyl-17-oxosparteine iodide monohydrate, respectively. The geometry of theN-methyl cations explains the differences in reactivities of the free bases with methyl iodide in the quaternization reaction. The axial hydrogen atoms of the methylene groups C(3), C(5), C(11) (in both compounds), and C(17) (in 15-oxosparteine only) shield the N(1) nitrogen electron pair. Three of the four piperidine rings in both cations exhibits similar conformations: ringsA andB-distorted chair, ringC-distorted sofa. The oxo substituent at the C(15) atom in the fourth ring,D, inN(1)-methyl-15-oxosparteine causes the 1,3-diplanar form, while that ring inN(1)-methyl-17-oxosparteine cation adopts the chair conformation. The formation of quaternary cation requires an adjustment in the ringC conformation of the parent 15-oxosparteine skeleton from a distorted boat to a distorted sofa; the max. difference in equivalent torsion angle values is 31.4°.