CRYSTAL STRUCTURE OF MONOCROTALINE

Abstract

The crystal structure of monocrotaline (C16H23NO6), a pyrrolizidine alkaloid has been determined.It crystalizes in the orthorhombic system,space group P212121. The unit cell which contains four molecules has the dimension a=13.578 (3), b=11.433 (2) and c=10.153 (2) A A total of 1605 pairs of reflections (HKL and HKL) are recorded on a Philips four-circle diffractometer. The crystal structure of monocrotaline is determined and refined by the (GC-79) (ALGOL 60)program system developed by the present author. Of the 179 |EAs| greater than 1.5, 171 have their phases determined and an E map reveals all 23 nonhydrogen atoms of monocrotaline as the highest peaks. The initial R value, for all the Fs of these 23 atoms, is 0.30. The final refinement results in a residual E=0.076. The only hydrogen bond formed in this crystal is between the hydrogen of O(17) in one molecule and the N(4) in the other translated one unit cell away in the C axis. The dihedral angle between C(1)-C(2) and C(9)-C(10) is 65.6°. The structural features of monocrotaline are noted and compared with those of five other pyrrolizidine alkaloids.