A Novel Hydrolyzable Tannin and Related Compounds Isolated from the Leaf Surface of Chrysolepis sempervirens

Abstract

ABSTRAC~.-A novel hydrolyzable tannin, chinquapinic acid [3], was isolated from the MeOH extract of the epidermal powder found on the leaf underside of CbrysokpiS ~anpervimU inaddition totwoknown tannins,vescalagin11]andcastalagin(2]. Thestrucnveofchinquapinic acid was established through spectroscopic data and auto-conversion to vescalagin. Scanning electron microscopy showed the yellowish powder to be crystal-like in appearance. These tannins are first examples for this class of compounds found as exudates on a plant surface. Chrysolepis sempervirens (Kellogg) Hjelmq. formerly Castenopsis sempewirens (Fagaceae), commonly referred to as bush chinquapin, is an evergreen shrub growing on rocky slopes of the Sierra Neveda and in central Oregon. We found the leaf underside of Chr. sempewirens densely covered with agold-colored powder that was easily scraped off. This material was previously believed to be composed of feltlike hairs (1). However, scanning electron microscopy showed the leaves to be covered with crystal-like powders which dissolved in MeOH. This indicated that the powder consists of organic chemicals. Our interest was to discover what chemicals are exuded and what role they play in plants. Many studies have been reported that plants secrete chemicals such as sugars, enzymes, and waxes, and that chemicals exuded onto the plant surface may act as defense substances against attack from insects (2) or microorganisms (3). We now report the isolation, structure determination, and biological activity of a novel hydrolyzable tannin and two known related tannins from Chr. sempvirens.