5,5'-Dithiobis(2-nitrobenzoic Acid) → N-[4-(5-carboxypentylcarbamoyl)-cyclohexylmethyl]-2-(hydroxy)ethyl thiosuccinimide

Mercaptoethanol (0.0045 ml of 1.43M solution in dimethylformamide, 6.4×10-6 mol) was added to SMCC-caproate (0.016 ml, 6.4×10-6 mol) in pyridine (see Example 6). The solution was gassed with argon and the tube sealed. After 12 hr at room temperature, no thiol remained (as determined by reaction with DTNB) and the solvents were removed in vacuo. The residue was dissolved in 0.03 ml of 0.2M potassium phosphate, pH 7, to make a 213 mM solution of the desired compound (see FIG. 1D).