improve the oral bioavailability of a recently discovered, novel structural class of 5-HT1A receptor agonists: aryl-[4-(6-R-pyridin-2-ylmethyl)-amino]-methyl}-piperidin-1 -yl-metha none. Incorporation of a fluorine atom in the beta-position to the amino function in the side chain led to analogues that exhibited, in general, enhanced and long-lasting 5-HT1A agonist activity in rats after oral administration