A six-step semisynthetic approach towards chiral nonracemic pyrrolo-allocolchicinoids
starting from naturally occurring colchicine was developed. The synthetic scheme includes
an electrocyclic tropolone ring contraction to afford allocolchicinic acid followed
by the Curtius reaction, giving the corresponding aniline. The Sandmeyer reaction
and copper-mediated hydrazination gave hydrazine-substituted allocolchicine. This
was introduced into the Fischer indole synthesis, affording libraries of regioisomeric
indole-based allocolchicine congeners.
Key words
colchicine - pyrrolo-allocolchicinoids - Fischer indole synthesis - tubulin - anti-tubulin
agents