Patent ID: 7417042

Claim:
A compound having a structure of formula I or a pharmaceutically acceptable salt thereof, wherein X is O, NH, or N-alkyl; Y is NH, N-alkyl, O, or C(R 9 ) 2 ; Z is O or C(R 9 ) 2 ; R 1 , R 2 , R 3 , and R 4 are all hydrogen; each R 5 , R 6 , R 7 , R 8 , and R 9 is independently selected from hydrogen, C 1-6 alkyl, C 1-6 hydroxyalkyl, C 1-6 alkoxyalkyl, aryl, and C 1-6 aralkyl, each of which is optionally substituted with a group selected from alkyl, amide, amine, carboxylic acid or a pharmaceutically acceptable salt thereof, carboxyl ester, thiol, and thioether; m is an integer from 0 to 2; and n is an integer from 0 to 2.