9 [C~(CHZ~ NH (CH~)~ NH (CH~)~ OP (O)(OH)~ I is formed, resulting from the acid- catalyzed breakdown of the PN bond in the nine-membered ring compound 13. At pH 2.2, the presence of chloride ion affected neither the stability of 1 nor the contribution of the two competing hydrolytic pathways. At pHs ranging from 3.4 to 8.6, there is little degradation of 1 since more than 95% of initial 1 was still present after 7 days at 20 “C. Under physiological ...