Phyllomeroterpenoids A-C, Multi-biosynthetic Pathway Derived Meroterpenoids from the TCM Endophytic Fungus Phyllosticta sp. and their Antimicrobial Activities

Phyllomeroterpenoids A−C (1−3), multi-biosynthetic pathway derived meroterpenoids from amino acid/pentose phosphate/terpenoid pathways, were isolated from the TCM endophytic fungus Phyllosticta sp. J13-2-12Y, together with six biosynthetically related compounds (4−9). All structures were determined by extensive spectroscopic analysis, chemical derivatization, and ECD experiments. A plausible biosynthetic pathway of 1−3 was proposed. In addition, the antimicrobial activities of all isolated compounds were evaluated against Staphylococcus aureus 209P (bacterium) and Candida albicans FIM709 (fungus).

The structure of 1 is composed of a guignardone moiety and a guignardianone moiety, so the observed ECD of 1 should result from the summed contributions of these two moieties based on the ECD additivity rule in diketones 19 . According to the structure, 7 can represent the contribution of the guignardone moiety, while 4 or the enantiomer of 4 can represent the contribution of the guignardianone moiety. The simulated ECD curve of 1, which was the sum of the experimental ECD data of 4 and 7, was similar to that of the experimental ECD curve of 1 (Fig. 3), therefore we deduced that the configuration of C-11′ in 1 should be the same as that in 4. Thus, the absolute configuration of 1 was determined as 4S, 6R, 9S, 10R, 14R, 11′S.
Phyllomeroterpenoid B (2) (Table S2) and the comparison of NMR data with (S, Z)-guignardianone C (4) (Table S4) revealed that 2 was the ester of a guignardone-type meroterpenoid and a guignardianone unit. A precise comparison of 1D NMR data of 2 (Table 1) Table S5) showed an obviously downfield shifted carbon at C-15, which suggested that the esterification was at C-15 in 2. Therefore, the planar structure of 2 was established as shown in Fig. 1. Combined with the carbon NMR data comparison with (S, Z)-guignardianone C (4) (Table S4), the key NOESY correlations (Table S2) between H-5′/H-9′ and H 3 -13′/H 3 -14′ revealed the configuration of the double bond of ∆ 2′ as Z. With the same alkaline hydrolysis experiment ( Figures S4-S6) and the comparison analysis of the simulated ECD with the experimental ECD data (Fig. 4) as described in 1, the absolute configuration of 2 was determined as 4S, 6R, 9S, 10R, 14R, 11′S.
Phyllomeroterpenoid C (3) was obtained as a yellowish oil, and its molecular formula was the same as that of 1 (C 31 H 34 O 9 ) as determined by HRESIMS. Based on comparison of the NMR data with (S, Z)-guignardianone C (4) 15,16 and detailed NMR analyses (Table S3), the planar structure of 3 was established as shown in Fig. 1, and the assignments of NMR data can be found in Table 1.
With the same comparison analysis of the simulated ECD with the experimental ECD data (Fig. 6) as described in 1, the absolute configuration of 3 was determined as 4S, 6R, 9S, 10S, 12S, 14R, 11′S.
The antimicrobial activities of the isolated compounds were evaluated against Staphylococcus aureus 209P (bacterium) and Candida albicans FIM709 (fungus). All compounds exhibited different antimicrobial activities (Table 2). Especially, 6 displayed obvious antimicrobial activities against S. aureus 209P and C. albicans FIM709 with MIC values of 4 μg/mL.