sentence: Subsequently , Shimpukade et al. [ 163 ] reported , using TUG-891 , a more selective human FFAR4 agonist as a tool compound , for which , based on studies mutating relevant amino acids in the orthosteric binding pocket including Arginine at position 99 ( Arg99 ) , it could be shown that this compound is an orthosteric agonist [ 164 ] .