The present invention provides substituted pyrrolo-, furano-, and cyclopentylpyrimidine bicyclic compounds of Formula III, and Formula IV, and pharmaceutically acceptable salts, 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 and pharmaceutical compositions for treating tumor cells and inhibiting mitosis of cancerous cells.