Patent ID: 8318973

Claim:
A compound or a pharmaceutically acceptable salt thereof, selected from: wherein X is independently at each occurrence selected from: —CH 2 COO—; —CH(CH 3 )COO—; —CH 2 CH 2 OCH 2 COO—; —CH 2 CH 2 CH 2 CH 2 CH 2 COO—; —(CH 2 ) y COO—; and, —(CH 2 CH 2 O) z CH 2 COO—, where y is independently selected from 2, 3, 4 and 6-24 and z is independently selected from 2-24; R′ is selected from H, benzyl, and C 1-6 alkyl; p is independently selected from 1, 2, 3, and 4; and, provided that when X is solely —CH 2 COO— or —CH(CH 3 )COO— or —CH 2 CH 2 CH 2 CH 2 CH 2 COO—, then p is ≧2.