Triterpenoid saponins from the pulp of Sapindus mukorossi and their antifungal activities

Highlights

• Five previously undescribed saponins were purified from Sapindus mukorossi.

• 16 μg/mL of one compound caused more than 99.9% C. albicans cell death within 4 h.

• Three compounds exhibited moderate anti T. rubrum activities.

Abstract

Under the guidance of anti-fungal bioassay, four previously undescribed oleanane-type and one lupane-type triterpenoid saponins, along with twelve known analogues, were isolated from the extract of Sapindus mukorossi pulps. Their structures were determined on the basis of spectroscopic analysis and chemical methods. In vitro biotests, oleanolic acid 3-O-β-D-xylopyranosyl-(1 → 3)-α-L-rhamnopyranosyl-(1 → 2)-α-L-arabinopyranoside showed inhibitory activity against Trichophyton rubrum with MIC₈₀ value of 8 μg/mL, while oleanolic acid 3-O-α-L-arabinopyranosyl-(1 → 3)-α-L-rhamnopyranosyl-(1 → 2)-α-L-arabinopyranoside exhibited inhibitory activity against both Trichophyton rubrum and Candida albicans with MIC₈₀ values of 8 μg/mL.

Introduction

The genus Sapindus comprises approximately 13 species and is widely distributed throughout tropical and subtropical regions of Asia, with four species and a variant present in Southern China (Delectis Florae Reipublicae Popularis Sinicae Agenda Academiae Sinicae Edita, 1985). Phytochemical investigations on the genus Sapindus have revealed its predominant specialized metabolites as triterpenoid saponins, some of which displayed molluscicidal, anti-inflammatory, cytotoxic, and anti-platelet aggregation activities (Huang et al., 2003, Huang et al., 2007, Huang et al., 2008, Takagi et al., 1980). Sapindus mukorossi Gaertn. (Sapindaceae) is a deciduous tall tree, whose fruits have been used as expectorant and natural surfactantsin ancient China (Yunnan Institute of Botany, 1972). In recent years S. mukorossi has attracted much attention for its fruits as ingredients of shampoo and cosmetic cleansers. However, there are only a few reports on the bioactive constituents of this S. mukorossi, which encouraged us to investigate it for previously undescribed and bioactive compounds (Kuo et al., 2005, Ni et al., 2006, Zhang et al., 2014). Therefore, we performed chemical investigation on the pulps of S. mukorossi under the guidance of in vitro anti-fungal bioassay. As a result, five previously undescribed triterpenoid saponins including oleanane (1–4) and lupine types (5), along with twelve known analogues (6–17) (Fig. 1), were isolated. Herein, this paper reports the isolation and structure elucidation of the previously undescribed compounds and biological activities of all the isolated compounds.