HETEROCYCLES

Note | Special issue | Vol. 82, No. 1, 2010, pp. 839-842
Received, 7th April, 2010, Accepted, 7th May, 2010, Published online, 10th May, 2010.
DOI: 10.3987/COM-10-S(E)18

■ Dehydrofuligoic Acid, a New Yellow Pigment Isolated from the Myxomycete Fuligo septica f. flava

Akinori Shintani, Kazufumi Toume, Yukinori Yamamoto, and Masami Ishibashi*

Department of Natural Products Chemistry, Graduate School of Pharmaceutical Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

Abstract

Dehydrofuligoic acid (1), a new yellow pigment with a chlorinated polyene-pyrone acid structure, was isolated from field-collected fruit bodies of the myxomycete Fuligo septica f. flava, and its structure was elucidated from spectral data.

During our search for bioactive natural products from myxomycetes,1 we have reported the isolation and structural elucidation of a new chlorinated polyene-pyrone acid compound, fuligoic acid (2),2 from field-collected materials of fruit bodies of Fuligo septica f. flava from Kochi prefecture in Japan. Recently, we further investigated the extract of this myxomycete, resulting in the isolation of a new yellow pigment, and here we describe the isolation and structure elucidation of the new compound, named dehydrofuligoic acid (1).

Fruit bodies of the myxomycete Fuligo septica f. flava, collected in Kochi Prefecture, Japan, were extracted with MeOH and acetone. The combined extracts were subjected to ODS column chromatography, followed by purification with a Sephadex LH-20 column to give a new yellow pigment, dehydrofuligoic acid (1), in 0.022% yield.
The negative ESIMS spectrum of 1 showed a quasi-molecular ion peak at m/z 307 (M−H)− together with its isotopic peak at m/z 309 in a ratio of ca. 3׃1. This isotopic pattern of 1 suggested the presence of one chlorine atom, and its molecular formula was revealed as C15H13O5Cl by HRESIMS data at m/z 307.0338 [calcd for C15H12O535Cl, (M−H)−, 307.0373] and at m/z 309.0360 [calcd for C15H12O537Cl, (M−H)−, 309.0344]. Negative HRESIMS showed significant fragment ion peaks at m/z 265.0462 [calcd for C14H12O337Cl, 265.0445] and 263.0491 [calcd for C14H12O335Cl, 263.0475], which corresponded to isotopic ions for the (M－H－CO2)－ ion, and at m/z 227.0719 [calcd for C14H11O3, 227.0708], which was assignable to the (M－H－CO2－HCl)－ ion. Observation of these ions implied the presence of a carboxylic acid and one chlorine atom. The IR absorption bands observed at 3420 (broad), 1680, and 1600 cm-1 were suggestive of the presence of a carboxyl group and a conjugated carbonyl group. The 1H NMR spectrum of 1 in DMSO-d6 (Table 1) showed signals for a methoxy group at δH 3.81 (3H, s) and many olefinic protons, and the 13C NMR spectrum revealed the presence of fourteen sp2 carbons, including one ester or lactone (δC 163.0) and one acid carbonyl carbon (δC 163.0), thus accounting for 8 of 9 unsaturations. The remaining unsaturation was therefore ascribable to one ring. These 1H and 13CNMR data were almost identical to those of fuligoic acid (2),2 and the molecular formula suggested that 1 had two hydrogen atoms fewer than 2. The 1H and 13C NMR spectra of 1 did not show the signals for an sp3 methylene and an sp3 oxymethine carbon due to the C-3 and C-4 positions of 2, respectively. The UV absorption maxima of 1 were observed at longer wavelengths (λmax 406, 386, and 303 nm) than those of 2 (λmax 340, 325, and 233 nm), implying that 1 had a longer conjugation system than 2. Analysis of the 2D NMR data (Figure 1) suggested that 1 had an unsaturated bond at the C-4/C-5 position (H-4, δC 6.27; C-4, δC 101.4; C-5, δC 158.3), forming an α-pyrone ring, from the 1H-1H COSY cross peak for H-2/H-4 and HMBC correlations for H-2/C-1, H-2/C-3, H-2/C-4, H-4/C-2, H-4/C-3, H-4/C-5. A methoxy group [δH 3.81 (3H, s); δC 56.6] was assigned to the C-3 position from the HMBC correlation from methoxy protons [δH 3.81 (3H, s)] to C-3 (δC 170.9). A polyene side-chain was shown to be attached to the C-5 position from the HMBC correlations for H-4/C-6, H-6/C-5, and H-7/C-5, and this side-chain was assigned as a tetraene (C-6 to C-13) with a carboxyl group attached to the terminal (C-14) from 13C NMR chemical shift data (Table 1). A doublet with low-field resonance (δH 7.17) in the 1H NMR spectrum of 1 was assigned to the β-position (H-12) from the carboxyl group (C-14), which was consistent with the HMBC correlation observed from H-12 to C-14. A chlorine atom was located on the remaining sp2 quaternary carbon at δC 137.5, which was assigned to the α-position (C-13) of the carboxyl group (C-14) from the HMBC correlations for H-12/C-13 and H-12/C-14. From all of these results, the structure of compound 1, named dehydrofurigoic acid, was revealed as a 4,5-dehydroderivative of fuligoic acid (2).2

EXPERIMENTAL
General Procedures UV spectra were obtained on a Shimazu UV mini-1240 spectrometer. IR spectra were measured on ATR on a JASCO FT-IR 230 spectrophotometer. The NMR spectra were recorded on a JEOL JNM ECP 600 spectrometer with deuterated solvents, the chemical shift of which was used as an internal standard. Negative ESIMS were measured on an Exactive (Thermo Scientific).
Organism The fruit bodies of Fuligo septica f. flava were collected in Konan-shi, Kochi Prefecture, Japan in July 2008 and identified by Y.Y. A voucher specimen (#31365) is maintained by Y.Y.
Extraction and isolation The wild fruit bodies (17.4 g) were extracted with 90% MeOH (200 mL x 2) and 90% acetone (100 mL x 2). The combined MeOH and acetone extracts (743 mg) were subjected to ODS column chromatography (20 x 200 mm) eluted with 0–100% MeOH in water, and the fraction (15 mg) eluted with 25% MeOH in H2O was further separated by LH-20 column chromatography twice (1st, 15 x 220 mm, MeOH; 2nd, 10 x 220 mm, MeOH) to afford compound 1 (3.8 mg).
Dehydrofuligolic acid (1): Yellow powder; UV(MeOH) λmax 406 (ε 10000), 386 (13000), and 303 nm (6600); IR (ATR) νmax 3420 (broad), 1680, 1600, 1460, and 1370 cm-1; 1H and 13C NMR (Table 1); (-)-ESIMS m/z 307 and 309 (M−H)−; (-)-HRESIMS m/z 307.0338 [calcd for C15H12O535Cl, (M−H)− 307.0373], m/z 309.0360 [calcd for C15H12O537Cl, (M−H)− 309.0344], m/z 265.0462 [calcd for C14H12O337Cl, (M−H−CO2)− 265.0445], m/z 263.0491 [calcd for C14H12O335Cl, (M−H−CO2)− 263.0475], and m/z 227.0719 [calcd for C14H11O3, (M−H−CO2−HCl)− 227.0708].

ACKNOWLEDGEMENTS
This work was partly supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science (JSPS).

References

1. M. Ishibashi, Yakugaku Zasshi, 2007, 127, 1369. CrossRef
2. A. Shintani, T. Ohtsuki, Y. Yamamoto, T. Hakamatsuka, N. Kawahara, Y. Goda, and M. Ishibashi, Tetrahedron Lett., 2009, 50, 3189. CrossRef
3. The 1H NMR spectrum of 1 showed the coupling constant for J6,7 to be 15.7 Hz, implying 6E-configuration, while coupling constants of other double bonds unfortunately remained unassigned due to overlapping signals, and their geometry was tentatively drawn here as analogous to compound 2.