By condensation of fumagillol [(3R,4S,5S,6R)-4-(1,2-epoxy-1,5-dimethyl4-hexenyl)-6-hydroxy-5-methoxy-1-oxaspiro[2.5]octane] (I) with chloroacetylisocyanate (II) by means of dimethylaminopyridine (DMAP) in dichloromethane.