... Journal ... Formation of the S-NO bond in papain is supported by several lines of evidences from both spectroscopic studies and chemical analyses. ... Scheme 1. Synthetic Approach toward Compounds 6 and 7 a. a (a) EDC, HOBt, Et 3 N, CH 2 Cl 2 . (b) NaNO 2 , MeOH/HOAc, 0 °C. ...