ph 2 with 1m hcl ph paper resulting in a biphasic solution the upper layer thf was removed and the aqueous layer was extracted with thf 3 u00d7 3 ml the combined organic layers were dried with mgso 4 and then concentrated under reduced pressure to afford diacid 24 as a white solid 21 mg 92 refer to the supporting information for specific synthetic details and characterization data for compounds 25 38 44 48 and 60 70 analogous to that reported for 24 below 1 phenylamino dibenzofuran 4 6 dicarboxylic acid 24 maldi ftms 347 0794 m z m u00b7 c 20 h 13 no 5 requires 347 0788 fig1 a shows an x ray crystallographic structure of ttr u2022 1 2 klabunde t et al nature struct biol 2000 7 312 321 the residues lining the binding site are displayed as stick models oxygen in red nitrogen in blue and carbon in gray with the protein 39 s connolly surface depicted in gray compound 1 is shown in both of its c 2 symmetry equivalent binding modes yellow and green the binding channel has 3 sets of depressions referred to as the halogen binding pockets hbps because they interact with the iodines of thyroxine compound 1 occupies only the outer portion of the binding pocket and fills both hbp1 and 1 u2032 the carboxylic acids of 1 are in proximity to the e nh 3 of k15 and k15 u2032 fig1 b shows a line drawing representation of the design of the 1 substituted dibenzofuran 4 6 dicarboxylic acids placed in the thyroxine binding pocket where x represents either an nh o or.