Seven New Drimane-Type Sesquiterpenoids from Cultures of Fungus Phellinus tuberculosus

Graphical Abstract Seven new drimane-type sesquiterpennoids, phellinuins A–G (1–7), together with one known compound 3β,11,12-trihydroxydrimene (8) were isolated from the cultures of mushroom Phellinus tuberculosus. Their structures were elucidated on the basis of NMR and MS spectroscopic data and by comparison with data reported in the literature. Electronic supplementary material The online version of this article (doi:10.1007/s13659-014-0002-x) contains supplementary material, which is available to authorized users.


Introduction
Phellinus is a genus of fungi in the family Hymenochaetaceae. Many species cause white rot. Its fruiting bodies, often growing on wood, are resupinate, sessile, and perennial. The flesh is tough and woody or cork-like, and brown in color [1]. The fungus Phellinus tuberculosus has a wide distribution in Yunnan province of China [2]. The crude extract of mushroom P. tuberculosus was reported to possess antioxidant activity, which exhibited potent radical scavenging activity [3]. However, the chemical constituents of P. tuberculosis has not reported yet. As our continuous search for natural products from higher fungi [4][5][6][7], we carried out the chemical investigation on cultures of P.
tuberculosus, which resulted in the isolation of seven new drimane-tpye sesquiterpennoids named phellinuins A-G (1-7) and one known compound (8) (Fig. 1). The structures of new compounds were determined on the basis of extensive spectroscopic analysis including NMR, MS, IR data, while the known compound was identified as 3b,11,12-trihydroxydrimene (8) by comparison with data reported in literature [8]. This paper describes their isolation and structural elucidation.  (Table 2) shows the presence of two methyls, six methylenes, four methines, and three quaternary carbons. In addition, the IR spectrum showed the presence of hydroxy group (3405 cm -1 ). Apart from one double bond, the remaining two degrees of unsaturation in 1 were assumed to be a bicyclic sesquiterpenoid. Detailed analysis of NMR data suggested that compound 1 should be a drimane-type sesquiterpenoid with a similar planar structure to that of 3a,11,15-trihydroxydrimene [9]. Analysis of 2D NMR data suggested that only Me-12 was oxygenated into an oxymethylene in 1, which was suggested by the HMBC correlations from d H 4.23 (1H, d, J = 11.8 Hz, H-12a) and 3.95 (1H, d, J = 11.8 Hz, H-12b) to d C 138.7 (s, C-8). The HMBC data further supported that the other parts of the planar structure of 1 were the same to those of 3a,11,15-trihydroxydrimene ( Fig. 2) [9]. In the ROESY spectrum (Fig. 2), the correlation of H-5/Me-15 suggested that C-14 was b oriented, while the correlation of Me-15/H-3, as well as the constant coupling of H-3 (dd, J = 11.8, 3.6 Hz), indicated OH-3 to be b oriented. On the basis of these data, the ROESY correlations of H-5/H-9 and Me-13/H-11 indicated that H-9 was a oriented, while Me-13 was b oriented. Therefore, compound 1 was established as 3b,11,12,14-tetrahydroxydrimene and named as phellinuin A.
Compound 2 (Tables 1  and 2) were very similar to those of compound 1, which indicated that both compounds had the same structure. However, the ROESY correlations of H-5/H-15 and H-15/H-3 indicated that Me-15 was oxygenated into an oxymethylene in 2, while C-14 should be a methyl (Fig. 2). Detailed analyses of other 2D NMR data suggested that the other parts of 2 were the same to those of   ). The IR spectrum displayed the absorption bands for C=O (1722 cm -1 ), OH (3418 cm -1 ), and C=C (1642 cm -1 ). All the NMR data suggested that compound 3 was closely related to 1 except one more O-acetyl group in 3. The Oacetyl group was substituted at C-11-as revealed by HMBC correlations from d H 4.30 (1H, dd, J = 12.0, 4.2 Hz, H-11a) and 4.20 (1H, overlap, H-11b) to d C 173.0 (s, OAc) and 52. 2 (d, C-9). The other 2D NMR data suggested that the other parts of 3 were the same to those of 1 (Fig. 2). Thus, the structure of compound 3 was elucidated as phellinuin C as shown in Fig. 1.
Compound 4 was also obtained as a colorless oil. HREIMS gave one pseudomolecular ion at m/z 312.1947 (calcd for C 17 H 28 O 5 , 312.1937). The 1D NMR data (Tables 1 and 2) were very similar with those of compound 3. However, the HMBC correlations from d H 4.70 (1H, d, J = 12.6 Hz, H-12a) and 4.53 (1H,d,J = 12.6 Hz, to d C 134.4 (s, C-8) and 173.0 (s, OAc) suggested that the O-acetyl group was substituted at C-12 in 4 rather than at C-11 in 3. The other parts of structure 4 were established to be the same with those of 3 by 2D NMR correlations (Fig. 2). Therefore, compound 4 was identified as phellinuin D.
Compound 5 was established as an O-acetyl derivative of 2, which was supported by the HMBC correlations from d H 4.32 (1H, dd, J = 11.4 and 4.2 Hz, H-11a) and 4.21 (1H, dd, J = 11.4 and 6.0 Hz, H-11b) to d C 137. 2 (s, C-8) and 173.0 (s, OAc). The other 2D NMR data suggested that the others parts of 5 were the same to those of 2. Therefore, the structure of compound 5 was established and named as phellinuin E.
Compounds 6 and 7 were identified as O-acetyl analogues of the known compound 3b,11,12-trihydroxydrimene (8) [8]. The HMBC data suggested that the O-acetyl group was substituted at C-11 in 6 and C-12 in 7, respectively (Fig. 2). Analyses of other 2D NMR data suggested that the other parts were the same to those of 8 (Fig. 2). Therefore, the structures of compounds 6 and 7 were established and named as phellinuin F (6) and phellinuin G (7), respectively.