A series
of newly synthesized hydroxylated analogues of triethyldesmosdumotin
B (TEDB) with a bicyclic B-ring exhibited a significantly different
mode of action for affecting microtubule dynamics and spindle formation
but had the same antiproliferative activity spectrum, including activity
against multidrug-resistant tumors. These analogues efficiently induced
cell cycle arrest at prometaphase and caused formation of immature
multipolar spindles. 6′-Hydroxyl TEDB-TB (<b>8</b>) disrupted
bipolar spindle formation but had a negligible effect on interphase
microtubules. On the basis of the predicted binding modes of the new
compounds with tubulin dimer, compound <b>4</b> forms three
hydrogen bonds (H-bonds) only with α-tubulin at the colchicine
site; in contrast, <b>8</b> forms H-bonds with both α-
and β-tubulin. We predict that, when a compound/ligand, such
as <b>8</b>, forms H-bonds to both α- and β-tubulins,
spindle formation is disrupted more than the dynamics of interphase
microtubules. This result may reflect the well-known greater dynamicity
of spindle microtubules as compared with interphase microtubules