Tabebuia bahamensis: A Major Source of Pharmacologically Important Ursolic Acid

Abstract

Leaves of Tabebuia bahamensis, collected on Abaco Island, Bahamas, were dried and extracted with dichloromethane to yield a crude extract. Using preparative flash column chromatography on silica gel, enabled the isolation of ursolic acid with an excellent yield of 2.06 percent based on the mass of dry leaves. Both the crude leaf extract and ursolic acid produced selective in-vitro cytotoxic activity on tumor cells from human mammary and bladder tissue. Ursolic acid also demonstrated antibacterial activity against Staphylococcus aureus. INTRODUCTION Commonly known as “five fingers,” Tabebuia bahamensis (North.) Britton, is a small tree in the Bignoniaceae family along with 110 other genera consisting of 650 species of flowering plants of which about 100 species belong to the Tabebuia genus (Rahmatullah et al., 2010; Ospina et al., 2013). The Five Fingers tree, which is endemic to the Bahamas, is now commonly observed in tropical and subtropical habitats, has small leaves with 3-5 leaflets that are slender, green on the upper surface and strongly whitish on the lower surface. The tree is slim with straight upright branches and grows well in properly drained, alkaline or acidic soils. Flowers vary in color from white to pink and the tree blooms throughout the year (Popenoe, 1980). Several species of the genus Tabebuia hold ethnopharmacological and ethnobotanical importance. In the Bahamas, the leaves of T. bahamensis are used as a tea for “bodily strain” and for relief of backache (Higgs, 1969). The leaf decoction of T. bahamensis has been used as a sex stimulant and aphrodisiac (Halberstein, 2005), and the plant has been an essential component of a “love potion” prepared on Andros Island of the Bahamas (Eshbaugh, 2014). In the current study, the biological activity of crude leaf extract from T. bahamensis and the isolation of ursolic acid in large quantities are detailed. To our knowledge, this is the first examination of the phytochemistry of T. bahamensis. MATERIALS AND METHODS Plant material. Leaves of T. bahamensis were collected December 16, 2000, on Abaco Island, Bahamas (26° 31.092′ N, 77° 4.258 W, 13 m asl). The plant was identified in the field by a qualified local ethnobotanical informant (Dolly Davis), and verified with a field guide (Nickrent et al., 1991). A voucher specimen (TABA2000) has been deposited in the herbarium of the University of Alabama in Huntsville. The leaves were cleaned of debris, chopped, air dried, and 594 g of chopped dry leaves were extracted by refluxing with dichloromethane for four hours using a Soxhlet extractor. The solvent was subsequently evaporated to yield 50.1 g of crude leaf extract. Preparative flash chromatography. The crude, dichloromethane leaf extract (25.0 g) was subjected to flash chromatography (Figure 1) using silica gel (230-400 mesh), in a 90 cm long × 5 cm diameter glass column. A hexane/ethyl acetate step Shrestha et al.: Tabebuia bahamensis: A Major Source of Pharmacologically Importa