Lanostane derivatives from the leaves and twigs of Garcinia wallichii

Highlights

• Four undescribed lanostanes were isolated from the leaves and twigs of Garcinia wallichii.

• The isolated lanostanes were evaluated for cytotoxicity.

• The acetoxy moiety at C-3 of the lanostane core appears to be crucial for their cytotoxicity.

Abstract

Bioassay-guided purification of the n-hexane and ethyl acetate extracts of the leaves and twigs of Garcinia wallichii led to the isolation of four previously undescribed lanostane triterpenes, wallichinanes F–I (1–4), together with four known compounds, wallichinane A (5), wallichinane B (6), friedelin (7), and lupeol (8). All structures were determined by means of spectroscopic techniques as well as comparison with literature data. Some isolated compounds were evaluated for cytotoxicity against a panel of cultured mammalian cancer cell lines. Wallichinanes G and H displayed weak cytotoxicity, whereas wallichinanes A, B, and F were found to be inactive in all the tested cell lines.

Introduction

Triterpenes are a large group of naturally occurring secondary metabolites found in many plant species as well as other organisms, such as fungi, bacteria, and marine sponges. Triterpenes have been reported to exhibit diverse biological properties including antitumor, antiviral, antimicrobial, and anti-inflammatory activities (Bui et al., 2016; Jamila et al., 2015; Elfita et al., 2009). Additionally, among privileged structural scaffolds, triterpenes have been studied for their potentials as multiple biological receptor targeting (Callies et al., 2015; Soural et al., 2015; Carvalho et al., 2010).

Garcinia wallichii Choisy, locally known in Thai as “Pawa Som”, is a medium-sized tree in the family of Guttiferae. Preliminary pharmacological screening study showed that the crude methanol (MeOH) extract of its leaves and twigs exhibited anti-inflammatory and analgesic effects (Panthong et al., 2009). Recently, we have isolated six lanostane triterpenes from the n-hexane extract of the fruits of G. wallichii. Among those, wallichinane D induced significant cytotoxicity against various cancer cell lines with ED₅₀ values ranging from 3.91 to 7.63 μM (Hongthong et al., 2016). Herein, we reported the isolation of four previously undescribed lanostane-type triterpenes, wallichinanes F‒I (1‒4) and four known compounds including wallichinanes A (5) and B (6) (Hongthong et al., 2016), friedelin (7) (Escobedo-Martinez et al., 2012), and lupeol (8) (Burns et al., 2000) (Fig. 1) from the n-hexane and ethyl acetate (EtOAc) extracts of the leaves and twigs of G. wallichii. Additionally, cytotoxic effects of some of these isolated compounds against a panel of mammalian cancer cell lines were described. The study on structure-activity relationship was also discussed.