Carbethoxylating agents as inhibitors of aldehyde dehydrogenase.

N,O-Dicarbethoxy-4-chlorobenzenesulfohydroxamate (1c) and O-carbethoxy-N-hydroxysaccharin (6), both potential carbethoxylating agents, inhibited yeast aldehyde dehydrogenase (AIDH) with IC 50 's of 24 and 56 μM, respectively. The esterase activity of the enzyme was commensurably inhibited. AIDH activity was only partially restored on incubation with mercaptoethanol (20 mM) for 1 h. On incubation with rat plasma, 1c liberated nitroxyl, a potent inhibitor Of AIDH. Under the same conditions, nitroxyl generation from 6 was minimal, a result compatible with a previous observation that nitroxyl generation from N-hydroxysaccharin (7), the product of the hydrolysis of the carbethoxy group of 6, was minimal at physiological pH. Since chemical carbethoxylating agents represented by the O-carbethoxylated N-hydroxyphthalimide, 1-hydroxybenzotriazole, and N-hydroxysuccinimide (8, 9, and 10, respectively) likewise inhibited yeast AIDH, albeit with IC 50 's 1 order of magnitude higher, we postulate that 1c and 6 act as irreversible inhibitors of AIDH by carbethoxylating the active site of the enzyme.