four homologues of pepstatin , the potent but poorly soluble inhibitor of aspartic proteinases , were synthesized by coupling to the c-terminus of the natural pentapeptide the following amino acid residues : l-arginine methyl ester , l-aspartic acid , l-glutamic acid and the dipeptide l-aspartyl-l-arginine .
C0002520
amino acid
C0061472
l-glutamic acid