Patent ID: 7790902

Claim:
A compound of the formula or a pharmaceutically acceptable salt, or prodrug thereof, wherein: X 1 is O; one of R 1 and R 2 is H and the other is a C 1 -C 10 alkyl substituted with —(CH 2 ) t (5-10 membered heterocyclic), or R 1 and R 2 are H wherein t is an integer from 0 to 5; R 3 is H or C 1 -C 10 alkyl substituted with —(CH 2 ) t (C 6 -C 10 aryl), wherein t is an integer from 0 to 5; and said aryl and heterocyclic groups are optionally substituted by 1 to 3 substituents independently selected from halo.