The present invention provides substituted cyclopenta and cyclopentyl pyrimidine bicyclic compounds of Formula III, and 5,6-saturated and unsaturated and pharmaceutically acceptable salts, prodrugs, solvates, and hydrates thereof, having antimitotic activity, anti-multidrug resistance activity, such as for example P-glycoprotein inhibition, and antitumor activity, and which inhibit paclitaxel sensitive and resistant tumor cells. Also provided are methods of utilizing these compounds for treating tumor cells and inhibiting mitosis of cancerous cells.