Benzofurans from the Seeds of Styrax obassia

Abstract

Styrax obassia also known as ‘fragrant snowbell’ is a member of the Styracaceae family. It is a shrub or tree native to tropical and subtropical regions with the majority in eastern and southern Asia. The genus Styrax is different from other genera of this family due to the production of resinous material, usually secreted when the barks and trunks are injured by sharp objects. This resin, in the past considered as a miraculous remedy in several parts of Asia and America, has been used in traditional medicine to treat inflammatory diseases. Its resin was used by Romans, Egyptians, Phoenicians and Ionians as incense and in therapeutics. The pericarps are used as washing soap (skin elastic material), cough medicine and a piscicidal agent. Styrax species contain egonol, a natural benzofuran, which is known to be an effective pyrethrum synergist. Earlier chemical studies on several Styrax species have revealed them to be a rich source of arylpropanoids, triterpenoids and their glycosides with various biological activities such as antisweet, antimicrobial, antiproliferative, cytotoxic and matrix metalloproteinase-1-inhibitor. However, careful literature survey of Styrax species revealed that Styrax obassia has not been studied much so far except for a few short reports. As a part of our on going research on chemical constituents from S. obassia, we isolated a hitherto unknown compound 1 along with four known compounds (2-5) from the seeds of S. obassia. This paper deals with the isolation and structure elucidation of these compounds by their comprehensive spectroscopic analysis including 2D NMR. The C NMR data of known compound 5 is being reported here for the first time. Compound 1 (Figure 2) was obtained as a colorless crystal and exhibited UV absorbance in CHCl3 at 242 and 318 nm. The IR spectrum of compound 1 showed the bands at 2954, 1738, 1601, 1481, 1232 and 941 cm. Compound 1 showed a molecular ion peak at m/z 382 ([M], base ion) in the EIMS spectrum, its molecular formula could be determined as C22H22O6 by HREIMS m/z: 382.1416 ([M] , calcd. for C22H22O6, 382.4141). H and C NMR signals of compound 1 (Figure 1) were assigned by the interpretation of the DEPT, COSY, HMQC and HMBC spectra (Table 1). The C NMR spectrum of compound 1 showed the signals for 22 carbons which were distinguished into two methyl (δC 9.2, 56.1), five methylene (δC 27.6, 30.7, 32.4, 63.6, 101.2), six methine (δC 100.3, 105.5, 107.4, 108.5, 112.3, 119.2) and nine quaternary (δC 124.6, 131.0, 136.9, 142.5, 144.7, 147.9, 148.0, 156.1, 174.5) carbons with the help of DEPT experiments. Upon integration H NMR spectrum of compound 1 showed the presence of 22 protons. Most of the H and C NMR signals of compound 1 were similar to those of egonol which is also isolated in this work, besides the extra H NMR signals at δ 1.15 (3H, J = 7.5 Hz) and 2.34 (2H, q) and their corresponding C NMR signals at δC 9.2 (methyl carbon), δC 27.6 (methylene carbon) and δC 174.5 (quaternary carbon) from H-C one bond (HMQC) experiment for a propanoyl moiety. The position of propanoyl moiety was confirmed from the HMBC experiment. The proton H-3 of egonol moiety correlated with the carbon 1a of propanoyl group in the HMBC experiment, which confirmed the position of a propanoyl moiety in compound 1 (Figure 1). On the basis of these spectroscopic data compound 1 was