Studies on Aldose Reductase Inhibitors from Fungi. II. Moniliformin and Small Ring Analogues

The fungal metabolite moniliformin and several small ring analogues were evaluated for potential substrate and inhibitory activity in the rat lens aldose reductase (AR) assay. Even though all of these compounds possess carbonyl moieties and structural similarities to AR substrates, none were found to function as substrates over a concentration range of 1.0 mM to 10 μM. All of the compounds did display inhibitory activity with IC50s ranging from 19–110 μM. The most inhibitory compounds were the four-membered ring moniliformin (ICI 19 μM), the five-membered analogue croconic acid (IC50 28 μM) and six-membered derivative tetrahydroxy p-benzoquinone (1C50 23 μM). Modification of moniliformin by methylation (methyl moniliformin) or hydroxylation (squaric acid) resulted in a significant decline in inhibitory activity. All of the compounds evaluated except moniliformin displayed uncompetitive, non-competitive or mixed-type kinetics relative to the substrate (glyceraldehyde) and cofactor (NADPH), kinetic ...