Design and synthesis of inhibitors of N8-acetylspermidine deacetylase.

Analogues of N8-acetylspermidine (1) were synthesized as potential inhibitors of the cytoplasmic enzyme N8-acetylspermidine deacetylase. The compounds were assayed for their ability to inhibit the deacetylation of 1 in a cytosolic fraction from rat liver. The apparent Ki values were determined by Dixon plots. The apparent Km of 1 for this enzyme is 11.0 microM. It was found that compounds which lacked the N1 or the N4 of spermidine were less effective at competing for the enzyme than the substrate. All compounds with acyl substituents larger than acetyl were less potent inhibitors than the corresponding acetylated derivatives. Thus, the enzyme's selectivity as a deacetylase seems to be attributable to steric hindrance which occurs with larger acyl groups. The N8 of the substrate is not essential for its binding to the enzyme. Replacement of N8 with a CH2 group gives the ketone 14, which has an apparent Ki of 0.18 microM, 60-fold lower than the apparent Km of 1. The inhibitory potency of 14 is retained in compounds substituted at the N1 position. The N1,N1-dimethyl and the N1,N1-diethyl analogues (15 and 16) of 14 have apparent Ki values of 0.096 and 0.10 microM, respectively. These agents are the most potent inhibitors of N8-acetylspermidine deacetylase reported, and they are promising tools for use in determining the physiological function of N8-acetylspermidine deacetylation.

Metabolism of N1-acetylspermidine and N8-acetylspermidine in rats.

Metabolism of N1-acetylspermidine and N8-acetylspermidine in rat liver and kidney was studied in vivo. N1-Acetylspermidine was metabolized primarily to putrescine while N8-acetylspermidine underwent deacetylation to yield spermidine. The rate of metabolism of these two compounds was much greater than that of spermidine. The rate of metabolism of N8-acetylspermidine exceeded that of N1-acetylspermidine in both liver and kidney. These rapid rates of metabolism could at least in part account for the low levels of these two compounds found in tissues. The differences in routes of metabolism of N1-acetylspermidine and N8-acetylspermidine may indicate differences in cellular functions of the two compounds.