The crystal structure of colchicine. A new application of magic integers to multiple-solution direct methods

Abstract

The mitotic spindle inhibitor colchicine, C22H25NO6, crystallizes as a dihydrate in space group P21, a = 17.08, b = 10.70, c = 13.88 A, fl = 117.9 °, Z = 4(C22H25NO6.2H20)/unit cell. The crystal structure was solved by a multiple-solution direct method in which unknown starting phases ~l are represented using 'magic integers': tp I = mix. An appropriate choice of integers m I and sampling of the variable x allows a drastic reduction in computing time and a great increase in structure-solving capability compared to the widely used method in which all unknown phases are permuted among the four values 45, 135, 225, 315 °. The crystal structure of colchicine dihydrate was refined by least squares to R = 0.052 for 2322 observed X-ray reflections. The two independent colchicine molecules have very similar conformations in the crystal. The troponoid rings have alternating bond lengths, and are not precisely planar. These rings make dihedral angles with the planar benzene rings of 53 ° in one molecule of eolchicine, 51 o in the other. The four independent water molecules are all found in a distinct region in the crystal, which is held together by a complex hydrogenbond network. Two methoxy-group O atoms of colchicine act as hydrogen-bond acceptors, the one on the troponoid ring participating in a bifurcated hydrogen bond.Colchicine (I), the principal active substance of the autumn crocus, has a remarkable range of biological effects. The most studied of these is its arrest of mitosis, believed to result from the specific strong binding of eolehicine to the protein tubulin, preventing the assembly of tubulin into mierotubules which form the mitotic spindle (Soifer, 1975). Colchicine is also capable of relieving the pain of gout (for which it has been used since ancient times), of inducing polyploidy * Present address:

2:1 Adduct of colchiceine acetate and ethyl acetate

“…This favours the first conformation previously mentioned. The puckering of ring C is comparable to that found in colchicine (Lessinger & Margulis, 1978a) as evidenced by the sum of these torsion angles.…”

“…In order to try to clarify the relationships between structure and biological activity in the products of the colchicine series the crystal structures of colchicine (I) (R = CH3) (Lessinger & Margulis, 1978a), its inactive isomer, isocolchicine (II) (R = CH3) (Lessinger & Margulis, 1978b), and other derivatives (Margulis, 1974(Margulis, , 1977Koerntgen & Margulis, 1977;Clark & Margulis, 1980;Brossi, R6sner, Silverton, Iorio & Hufford, 1980;Margulis & Lessinger, 1978;Margulis, 1975;Silverton, 1979) have recently been determined. On the other hand, Blad6-Font (1977a,b, 1978 has synthesized some new derivatives of colchicine with the same aim in view.…”

Structure of (7S)-N-acetyldemecolcine, C23H27NO6

“…Miravitlles, Solans, Blade-Font, Germain & Declercq (1982) show a figure and some torsion angles corresponding to (7S)-colchiceine acetate but their table inverts the values for comparison with the previous literature. Since unnatural colchicine is not readily available, it seems probable that all of the compounds have the 7S configuration which was established for colchicine itself by Corrodi & Hardegger (1955) (Lessinger & Margulis, 1978b); (4) colchiceine (Silverton, 1979); (5)N-acetyldemecolcine (this paper).…”

Structural studies of colchicine derivatives. V. The structure of 6,7-didehydrocolchiceine, C21H21NO6

“…'s is 2 °. 2 3 7 9 4 5 2 1 3 i (I) 6,7-Didehydroeolchieeine: present work; (II) acetylanhydroeolchieine (Miravitlles, Rius, Blad&Font & Germain, 1983); (III) isocolehicine (Lessinger & Margulis, 1978b); (IV) eolchicine (Lessinger & Margulis, 1978a); (V)eolchieeine (Silverton, 1979); (VI) 7-deaeetamidoeolehiceine (Rius, Molins, Miravitlles & Bladr-Font, 1984); (VII) eolehiceine benzoate (Molins et al, 1985) and (VIII) colchiceine acetate (Miravitiles et al, 1982). The conformation is influenced by three intramolecular hydrogen bonds.…”