“When tryptophan was replaced with other hydrophobic amino acids, such as phenylalanine, tyrosine, alanine, leucine, and isoleucine, the … were significantly reduced with MIC values of >128 µg/mL. Furthermore, a change in stereochemistry caused by d-arginine , and … of N-methyltryptophan , resulted in a two-… reduction of antibacterial activity.”