Inhibition of arabinose 5-phosphate isomerase. An approach to the inhibition of bacterial lipopolysaccharide biosynthesis.

Arabinose 5-phosphate ( A5P ) isomerase is a key enzyme in the biosynthesis of lipopolysaccharide, an essential component of the outer membrane of Gram-negative bacteria. The mechanism of the isomerase is envisioned to involve an enediol intermediate. A series of compounds, which are analogues of the substrates or intermediate, were tested as inhibitors of A5P isomerase with the belief that a good inhibitor would stop bacterial growth or render the cells more susceptible to other antibiotics or natural defenses. In a series of phosphorylated sugars, the order of isomerase inhibitory activity was as follows: aldonic acids greater than alditols greater than aldoses. Nonphosphorylated sugars were much less inhibitory. The best inhibitor was erythronic acid 4-phosphate (54), which had Km/Ki = 29. None of the compounds displayed antibacterial activity in vitro.