A Carboxylic Acid from Ilex integra

Abstract

(12E,14E,17E)-11-Hydroxy-12,14,17-dodecatrienoic acid was isolated from the stems of Ilex integra and its structure was determined on the basis of the spectroscopic data of its methyl ester.

Introduction

In the continuous search for physiologically active compounds in plants, we had a chance to investigate the chemical constituents of Ilex integra. This plant has already been studied by several workers [1,2,3] and triterpenes as well as its saponins have been reported so far [1,2]. Since it has been used as birdlime in Japan, leaves [1], fruits [2], and seeds [3] were investigated. Antimicrobial activities were reported for some triterpenes [2]. Although the fatty acid mixture was investigated using GC-MS [3], no structures were suggested. We have now found 11-hydroxy-12,14,17-dodecatrienoic acid in the leaves and stems of I. integra. The absolute configuration, however, was not determined. Here, we report the details of the new compound.

Results and Discussion

The methanol extract of I. integra was partitioned between EtOAc and water. The EtOAc soluble parts were subjected to silica gel column chromatography using gradients of hexane-EtOAc and CHCl₃-MeOH, as eluents. The main fraction was further purified by HPLC (hexane-EtOAc) to give a polar fraction, which was treated with CH₂N₂. The residue was further purified by column chromatography to afford a methyl ester 1.

Figure 1. Selected HMBC correlations of compound 1.

Figure 1. Selected HMBC correlations of compound 1.

The ester 1 exhibited a quasi-molecular ion peak at m/z 337 and its molecular formula was determined as C₂₁H₃₆O₃ by CIHRMS. The IR spectrum showed the absorptions at 3450 (OH), 1740 (CO), and 1650 (C=C) cm^-1. The ¹³C-NMR spectrum indicated the presence of three double bonds and a carbonyl group. The ¹H-NMR spectrum exhibited the methine proton at 4.16 ppm (Table 1). The COSY spectrum showed the connectivity from the C20 methyl group to the C11 methine proton, the sequence of which was supported by the fragmentation of the mass spectrum (Figure 2). The HMBC spectrum also indicated the connectivity shown by the arrows, drawn in the structure shown in Figure 1. The protons and carbons at C3-C10 were not assigned. The geometries of double bonds were assigned by the coupling constants. Namely, the J value for C12-C13 was 15 Hz, C14-C15 was 15 Hz, and C17-C18 was 15 Hz, suggesting all E-configuration. Consequently, the structure of the original natural product was established as (12E,14E,17E)-11-hydroxy-12,14,17-dodecatrienoic acid. The absolute configuration was not determined due to the minute quantity of the compound.

Figure 2. MS fragmentation pattern of compound 1.

Figure 2. MS fragmentation pattern of compound 1.