Proposed degradation in vitro of CW 1759-50. Addition of l-cysteine (reaction A) to a solution of CW 1759-50 at physiologic pH and temperature rapidly converts the parent molecule (CW 1759-50) to two adducts with a reaction half-time of 2.3 min. The adducts were identified by mass spectrometry as having the higher molecular weights compatible with the proposed products (adducts) of reaction A. Alkaline hydrolysis (reaction B) also occurs, at a much slower rate (half-time = 240 min), to the hydrolysis products shown. The products of alkaline hydrolysis are monoesters (hydrolysis products I and II) and amino alcohols (pseudoisoquinoline O and 1972-38). The degradation products of both reaction A and reaction B are positively charged quaternary ammonium compounds that are usually readily soluble in water and rapidly excreted in urine.