Structure–activity relationship studies on UK-2A, a novel antifungal antibiotic from Streptomyces sp. 517-02. Part 5: Roles of the 9-membered dilactone-ring moiety in respiratory inhibition

Abstract Several open-chained analogues of UK-2A, a novel antifungal antibiotic isolated from Streptomyces sp. 517-02, were prepared for structure–activity studies. The in vitro antifungal activities of these compounds against Rhodotorula mucilaginosa IFO 0001 and the inhibition of uncoupler-stimulated respiration in bovine heart submitochondrial particles (SMP) were evaluated. Oxidative potentials were measured by cyclic voltammetry. An analogue prepared from dihexyl l -glutamate showed comparable inhibitory activity as UK-2A.