Bioassay-guided isolation of novel and selective urease inhibitors from Diospyros lotus

Two new dimeric naphthoquinones, 5', 8'-dihydroxy-6, 6'-dimethyl-7, 3'-binaphthyl-1, 4, 1', 4'-tetraone ( 1 ; Di-naph±thodiospyrol D) and 5', 8'-dihydroxy-5, 8-dimethoxy-6, 6'-dimethyl-7, 3'-binaphthyl-1, 4, 1', 4'-tetraone ( 2 ; Di-naphthodiospyrol E), along with known naphthoquinones diospyrin ( 3 ) and 8-hydroxy diospyrin ( 4 ) were isolated from the chloroform fraction of extract of Diospyros lotus roots. Their structures were elucidated by advanced spectroscopic analyses, including HSQC, HMBC, NOESY, and J-resolved NMR experiments. The fractions and compounds 1 - 4 were evaluated for urease activity and phosphodiesterase-Ⅰ, carbonic anhydrase-Ⅱ and α-chymotrypsin enzyme inhibitory activities. Compounds 1 and 2 and their corresponding fractions showed significant and selective inhibitory effects on urease activities. The IC₅₀ values of 1 and 2 were 260.4±6.37 and 381.4±4.80 μmol·L^-1, respectively, using thiourea (IC₅₀=21±0.11 μmol·L^-1) as the standard inhibitor. This was the first report demonstrating that the naphthoquinones class showed urease inhibition.