Pyrazole alkaloids from watermelon (Citrullus lanatus) seeds.

Three new compounds, i.e. 1-[2-(5-hydroxymethyl-1 H -pyrrole-2-carbaldehyde-1-yl)ethyl]-1 H -pyrazole ( 1 ), 1-({[5-(α- d -galactopyranosyloxy)methyl]-1 H -pyrrole-2-carbaldehyde-1-yl}-ethyl)-1 H -pyrazole ( 2 ), and (4-hydroxyphenyl)methanol 4-[β- d -apiofuranosyl(1→2)- O -β- d -glucopyranoside] ( 3 ), were isolated from an extract of watermelon seeds. Compounds 1 and 2 were pyrazole-alkaloids with a pyrrole ring. This is the first study to show compounds with pyrrole and pyrazole rings in a molecule isolated from natural products. In the evaluation for melanogenesis inhibitory, compound 1 exhibited modest inhibitory activity on melanogenesis without cytotoxicity. Meanwhile compound 2 showed some inhibitory activity accompanied by some cytotoxicity. [ABSTRACT FROM AUTHOR]