SPSB2-iNOS inhibitory cyclic peptide-1 TFA is the TFA salt form of SPSB2-iNOS inhibitory cyclic peptide-1. SPSB2-iNOS inhibitory cyclic peptide-1 is an inhibitor for the interaction of SPRY domain and SOCS-box protein 2 (SPSB2) and iNOS , through binding SPSB2 on iNOS site with K D of 4.4 nM. SPSB2-iNOS inhibitory cyclic peptide-1 is resistant to the proteases pepsin, trypsin and α-chymotrypsin. SPSB2-iNOS inhibitory cyclic peptide-1 is stable in human plasma and in oxidative environment.