Patent ID: 8314214

Claim:
A method for preparing a compound of the formula: where R 1 , R 3 and R 4 are is selected from the group consisting of H, CH 3 , CH 2 CH 3 , and CH(CH 3 ) 2 ; and R 2 is: where R 5 , R 6 , R 7 and R 8 are independently hydrogen or C 1 to C 4 alkyl; or the esters or pharmaceutically acceptable salts thereof, comprising: a) combining a first compound of formula where X is CH 2 OH, C(O)H, CN or C(O)NR 1 2 , with a second compound of formula b) adding a reducing agent that is capable of reducing the nitro groups in the first and second compounds and forming an azo group, c) separating the desired azo coupling product from any mixture formed, and d) converting any X groups that are not in the form of carboxylic acid, carboxylate salt or ester groups to such groups, wherein the CH 2 OH or C(O)H group is oxidized to form a carboxylic acid, and wherein the CN or C(O)NR 1 2 groups are either hydrolyzed to form carboxylic acids or carboxylate salts, or, in the event that the CN or C(O)NR 1 2 groups are reduced by the reducing agent during the coupling of the nitro groups, such reduced groups are converted to carboxylic acid groups or carboxylate salts.