Molecular mechanics and molecular orbital calculations have been used to
determine the low-energy conformations of six biaryl analogues of colchicine
lacking the seven-membered B-ring. A comparison of the conformations resulting
from the different minimizations has been made, and these conformations were
also compared with those found in the solid state for the respective biaryl
analogues and the A/C-ring systems of colchicine and isocolchicine. The
barriers to rotation about the A/C-linkage of the analogues were estimated
from rotational plots. The MM+ calculations were not satisfactory for
estimating the barriers, whilst the MMX, MAXIMIN2 and AM1 values, although
agreeing on average only to within 16 kJ mol-1 ,
exhibited the expected trend in magnitude. This trend, however, did not
correlate with the inhibition of tubulin polymerization to microtubules.
Molecular orbital calculations of two-electron states for P-donor solid-state spin qubits
