Cyclohexanone and Phenolic Acid Derivatives from Endophytic Fungus Diaporthe foeniculina

Compound 1 was separated into acicular crystals. Its molecular formula C12H18O4 is established on the basis of (+) -Hresims M/Z 227.1274 (m + H)+ (the calculated value of C12H19O4, 227.1278), implying a fourth degree hydrogen deficiency. IR spectra of 1 logically reveal the presence of carbonyl and free hydroxyl functional groups by characteristic resonance absorption at 1,616 and 3,381 cm-1, respectively. 1H NMR data of 1 showed a series of typical proton signals, These signals have significant effects on the three oxymethyl fractions [δH 3.73 (1H, M, H-2), 3.29 (1H, M, H-3), 3.26 (1H, M, H-4)] and three methyl fractions [δH 1.48 (3H, D, J = 6.2Hz, H-9), 1.68 (3 H, s, H – 11), 1.16 (3 H, d, J = 6.3 Hz, H – 10)]. The 13C NMR data were combined with HSQC spectra of 1 to resolve 12 carbon resonances attributed to three methyl groups, one methylene group, four hypomethyl groups, and four quaternary carbons, including a carbonyl functional group (δC 204.1).

 

In 1H-1H COSY spectrum, the cross peak of H3-11/H-6/H2-5 indicated the presence of fragment A (C-11/C-6/C-5). From H3-10 to C-5 (δC 33.1), C-6 (δC 41.5) and C-7 (δC 204.1), H-11 to C-7, C-8 (δC 115.9) and C-8A (δC 171.0), H2-5 to C-7 and C-8A and fragments A coupling significantly indicates the presence of a cyclohexanone ring (ring A) with a carbonyl group at c-7 and two methyl groups linked at C-6 and C-8, respectively. In addition, The HMBC of H-2 to C-4 (δC 76.0) and C-8A, H-9 to C-2 (δC 79.1) and C-3 (δC 76.3) and 1H-1H COZY were obvious The correlation spin system B (C-4A /C-4/C-3/C-2/C-9) confirms the existence of pyran ring B. Therefore, the plane structure of 1 holds.

 

Key NOE correlations of H-2/H-4, H-4/ H-4A, and H-4A /H3-11 confirm that these protons are coplanar and designated as α oriented. Then, the NOE correlation between H-5 and H3-9 indicates that methyl groups on C-9 are β -oriented. So the relative configuration of 1 holds. The absolute configuration of 1 was finally determined by single crystal X-ray diffraction experiment, which provided perfect evidence for the absolute configuration of 1 with Flack parameter 0.02 (5). In addition, this conclusion was verified by ECD calculation. At this point, the structure analysis of compound 1 was completed, and its absolute structure was deduced as 2S, 3R, 4S, 4aS, 6S, commonly known as anisin A.

 

Compound 2 is acicular crystal. Its molecular formula is determined as C12H18O4 based on the protonated molecular peak at M/Z 227.1275 (M + H)+ in its HRESIMS spectrum, requiring four unsaturations. The 1D NMR data of 2 are almost the same as that of 1, except for the absence of hydroxyl group at the C-3 position of 2. This can be further enhanced by the 1H-1H COZY cross peak of H-2/H -3/H-4 and the main HMBC correlation from H3-9 to C-2 and C-3 and carbon manure of C-3 (δC 39.0).

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