PTP1B Inhibitory Secondary Metabolites from an Antarctic Fungal Strain Acremonium sp. SF-7394

Chemical investigation of the Antarctic lichen-derived fungal strain Acremonium sp. SF-7394 yielded a new amphilectane-type diterpene, acrepseudoterin (1), and a new acorane-type sesquiterpene glycoside, isocordycepoloside A (2). In addition, three known fungal metabolites, (−)-ternatin (3), [D-Leu]-ternatin (4), and pseurotin A (5), were isolated from the EtOAc extract of the fungal strain. Their structures were mainly elucidated by analyzing their NMR and MS data. The absolute configuration of 1 was proposed by electronic circular dichroism calculations, and the absolute configuration of the sugar unit in 2 was determined by a chemical method. The inhibitory effects of the isolated compounds on protein tyrosine phosphatase 1B (PTP1B) were evaluated by enzymatic assays; results indicated that acrepseudoterin (1) and [D-Leu]-ternatin (4) dose-dependently inhibited the enzyme activity with IC50 values of 22.8 ± 1.1 μM and 14.8 ± 0.3 μM, respectively. Moreover, compound 1 was identified as a competitive inhibitor of PTP1B.


Introduction
The fungal genus Acremonium has been identified in various sources such as soil, plants, and marine organisms [1]. Secondary metabolites derived from Acremonium species have been reported to contain steroids, terpenoids, meroterpenoids, polyketides, alkaloids, and peptides, which show a variety of biological activities, especially anti-bacterial, antifungal, and cytotoxic effects [1]. Some examples of these biologically active metabolites include cephalosporin antibiotics [2], cytotoxic heptelidic acid chlorohydrin [3], anti-fungal acremoxanthone A [4], and antibiotic cephaibol B [5]. In the course of our ongoing search for bioactive secondary metabolites from Antarctic-derived fungal strains [6,7], the EtOAc extract obtained from cultures of Acremonium sp. SF-7394 was subjected to several separation steps such as column chromatography (CC) using Sephadex LH-20, reversed phase (RP) C 18 , and silica gel as a stationary phase, and RP C 18 preparative HPLC. As a result, two novel fungal metabolites including an amphilectane-type diterpene, acrepseudoterin (1), and an acorane-type sesquiterpene glycoside, isocordycepoloside A (2), were isolated. Additionally, three known fungal metabolites including two cyclic heptapeptides, (−)ternatin (3) [8], [D-Leu]-ternatin (4) [9], and pseurotin A (5) [10] were identified ( Figure 1). The evaluation of the inhibitory effects of the isolated compounds on the enzyme activity of protein tyrosine phosphatase 1B (PTP1B) was also conducted in this study. Details of the isolation, structure elucidation, and biological evaluation of these compounds are described herein.

Results and Discussion
The HRESIMS of compound 1 exhibited a sodium adduct ion at m/z 309.2196 [M + Na] + , indicating a molecular formula of C20H30O (calcd for C20H30ONa, 309.2194) and therefore the presence of six degrees of unsaturation in the molecule. Analysis of the 1 H, DEPT, and 13 C NMR spectra of 1 (Table 1) revealed the presence of a 1,2,3,4-tetrasubstituted aromatic ring, four methyl groups (all were doublets in the 1 H NMR spectrum), five methylene units (one of which was oxygenated), and five methines. This information accounted for four units of unsaturation, suggesting that the compound must possess two additional ring systems. A detailed analysis of the 2D NMR data was next performed to establish the planar structure of 1. The direct connectivity between hydrogens and carbons in the molecule was established by analyzing the HMQC data, and the spin systems in the molecule were defined by interpreting the COSY data. The COSY spectrum of 1 indicated that the two methyl groups (CH3-16 and CH3-17) were correlated with the methine proton, H-15; this methine proton was further connected to the methylene protons H2-14 that in turn showed a correlation with the methine proton at δH 3.35 (H-1). Analysis of the COSY data further extended the sequential spin system from H-1 to H-7; the two methyl groups, CH3-18 and CH3-19, were located at C-3 and C-7, respectively, based on COSY correlations between the respective protons. In addition, the presence of an isolated oxy-methylene unit (H2-20) and two mutually ortho-coupled aromatic hydrogens were evident in the COSY data. The connectivity between these spin systems and quaternary carbons was established by analyzing the HMBC spectrum ( Figure 2). HMBC correlations of the aromatic hydrogens H-9 and H-10 with the carbons in the aromatic/olefinic carbon region allowed the complete assignment of carbon chemical shifts for the 1,2,3,4-tetrasubstituted benzene ring. Moreover, the HMBC correlation of H-10 to the oxygenated methylene carbon (C-20) connected this carbon to C-11. HMBC correlations of H-7 with C-8 and C-9 and H-4 with C-8 and C-13 provided the connection between C-7 and C-8, and between C-4 and C-13, respectively. Finally, the HMBC correlation of H-2 with C-12 provided evidence

Results and Discussion
The HRESIMS of compound 1 exhibited a sodium adduct ion at m/z 309.2196 [M + Na] + , indicating a molecular formula of C 20 H 30 O (calcd for C 20 H 30 ONa, 309.2194) and therefore the presence of six degrees of unsaturation in the molecule. Analysis of the 1 H, DEPT, and 13 C NMR spectra of 1 (Table 1) revealed the presence of a 1,2,3,4-tetrasubstituted aromatic ring, four methyl groups (all were doublets in the 1 H NMR spectrum), five methylene units (one of which was oxygenated), and five methines. This information accounted for four units of unsaturation, suggesting that the compound must possess two additional ring systems. A detailed analysis of the 2D NMR data was next performed to establish the planar structure of 1. The direct connectivity between hydrogens and carbons in the molecule was established by analyzing the HMQC data, and the spin systems in the molecule were defined by interpreting the COSY data. The COSY spectrum of 1 indicated that the two methyl groups (CH 3 -16 and CH 3 -17) were correlated with the methine proton, H-15; this methine proton was further connected to the methylene protons H 2 -14 that in turn showed a correlation with the methine proton at δ H 3.35 (H-1). Analysis of the COSY data further extended the sequential spin system from H-1 to H-7; the two methyl groups, CH 3 -18 and CH 3 -19, were located at C-3 and C-7, respectively, based on COSY correlations between the respective protons. In addition, the presence of an isolated oxymethylene unit (H 2 -20) and two mutually ortho-coupled aromatic hydrogens were evident in the COSY data. The connectivity between these spin systems and quaternary carbons was established by analyzing the HMBC spectrum ( Figure 2). HMBC correlations of the aromatic hydrogens H-9 and H-10 with the carbons in the aromatic/olefinic carbon region allowed the complete assignment of carbon chemical shifts for the 1,2,3,4-tetrasubstituted benzene ring. Moreover, the HMBC correlation of H-10 to the oxygenated methylene carbon (C-20) connected this carbon to C-11. HMBC correlations of H-7 with C-8 and C-9 and H-4 with C-8 and C-13 provided the connection between C-7 and C-8, and between C-4 and C-13, respectively. Finally, the HMBC correlation of H-2 with C-12 provided evidence for the connection between C-12 and the only remaining connection site C-1. Therefore, the tricyclic planar structure of 1 was assigned as shown to possess a hexahydro-1H-phenalene ring system. The carbons in compound 1 were numbered according to the precedent pseudopterosins [11]. The structure of 1 is recognized as a new amphilectanetype diterpenoid [12,13], and the name acrepseudoterin is proposed for compound 1. for the connection between C-12 and the only remaining connection site C-1. Therefore, the tricyclic planar structure of 1 was assigned as shown to possess a hexahydro-1Hphenalene ring system. The carbons in compound 1 were numbered according to the precedent pseudopterosins [11]. The structure of 1 is recognized as a new amphilectane-type diterpenoid [12,13], and the name acrepseudoterin is proposed for compound 1.   for the connection between C-12 and the only remaining connection site C-1. Therefore, the tricyclic planar structure of 1 was assigned as shown to possess a hexahydro-1Hphenalene ring system. The carbons in compound 1 were numbered according to the precedent pseudopterosins [11]. The structure of 1 is recognized as a new amphilectane-type diterpenoid [12,13], and the name acrepseudoterin is proposed for compound 1.  for the connection between C-12 and the only remaining connection site C-1. Therefore, the tricyclic planar structure of 1 was assigned as shown to possess a hexahydro-1Hphenalene ring system. The carbons in compound 1 were numbered according to the precedent pseudopterosins [11]. The structure of 1 is recognized as a new amphilectane-type diterpenoid [12,13], and the name acrepseudoterin is proposed for compound 1.  ) correlations for 1. The energy-minimized 3D structure was obtained by Macromodel (Version 12.5, Schrodinger LLC) program.
The relative and absolute configuration of 1 was determined by analyzing the NOESY data ( Figure 2) and electron circular dichroism (ECD) calculations ( Figure 3). The NOESY spectrum of 1 showed correlations of H-4 with H-1 and H-7, indicating that these protons are positioned on the same face of the ring system. On the other hand, NOESY correlations of H-5α with H 3 -18 and H 3 -19 demonstrated the placement of these methyl groups on the opposite face of the ring system, addressing the relative configuration of all the stereocenters in the molecule. The absolute configuration of 1 was proposed by TDDFT (time-dependent density functional theory) computational calculations. The experimental ECD (electronic circular dichroism) spectrum for 1 showed a positive Cotton effect near 250 nm and a negative Cotton effect near 230 nm. After the geometry optimization of each enantiomer of 1 to obtain minimum energy conformers, TDDFT calculated the ECD spectra for the enantiomers; (1S, 3R, 4R, 7R)-1 (1a) and (1R, 3S, 4S, 7S)-1 (1b) were generated. Comparison of the experimental and calculated ECD spectra indicated that the experimental ECD curve of 1 was almost identical to that calculated for 1b (Figure 3), suggesting a 1R, 3S, 4S, 7S absolute configuration for 1.
groups on the opposite face of the ring system, addressing the relative configuration of all the stereocenters in the molecule. The absolute configuration of 1 was proposed by TDDFT (time-dependent density functional theory) computational calculations. The experimental ECD (electronic circular dichroism) spectrum for 1 showed a positive Cotton effect near 250 nm and a negative Cotton effect near 230 nm. After the geometry optimization of each enantiomer of 1 to obtain minimum energy conformers, TDDFT calculated the ECD spectra for the enantiomers; (1S, 3R, 4R, 7R)-1 (1a) and (1R, 3S, 4S, 7S)-1 (1b) were generated. Comparison of the experimental and calculated ECD spectra indicated that the experimental ECD curve of 1 was almost identical to that calculated for 1b (Figure 3), suggesting a 1R, 3S, 4S, 7S absolute configuration for 1. Amphilectane-type diterpenoids possess a structurally interesting tricyclic carbon skeleton and are divided into two groups based on their shared structural characteristics. The pseudopterosin group possesses a tricyclic ring system containing an aromatic ring, while the amphilectane groups possesses a perhydrophenalene ring [13]. Amphilectanetype diterpenoids belonging to the pseudopterosin group such as pseudopterosins [11], helioporin E [14], and pseudopteroxazole [15] generally possess a fully substituted benzene ring and an isobutenyl group. In addition, most compounds of this class were isolated from marine invertebrates, as monoglycosylated forms with various biological activities such as anti-cancer, anti-malarial, and anti-inflammatory effects [11,13]. However, to the best of our knowledge, amphilectane-type diterpenoids with a tetrasubstituted benzene ring, as in 1, have not been reported yet. Therefore, compound 1 represents a new amphilectane-type diterpenoid of fungal origin possessing unique structural features.
The molecular formula of compound 2 (C21H34O7) was determined on the basis of its HRESIMS and NMR data, indicating five units of unsaturation. Analysis of 1 H, 13 C, and DEPT NMR data of 2 (Table 2) indicated the presence of three methyl groups, six methylene units (two of which are oxygenated), eight sp 3 methines (six of which are oxygenated including one acetal), one sp 2 methine, and three quaternary carbons (one of which is sp 2 carbon). As only the resonances for a trisubstituted olefin (δ 121.5 and δ 141.2) were observed in the NMR data to account for unsaturation units, it was deduced that the compound must possess four rings to fulfill the required units of unsaturation. There were nine 1 H NMR signals in the region for oxygenated sp 3 hydrogens. This observation, together with five sp 3 oxygenated methines, including one acetal (δ 95.4, δ 75.6, δ 74.5 δ 74.1 and δ 72.1) and one oxygenated methylene (δ 62.9) signal in the 13 C NMR spectrum, were suggestive of a hexose moiety. This was also supported by contiguous COSY correlations of five oxymethines and one oxymethylene. Further chemical shift considerations and analysis of coupling constants among respective oxymethines (Table 2), along with the HMBC correlation of H-1′ with C-5′ confirmed the presence of a glucopyranose unit in the Amphilectane-type diterpenoids possess a structurally interesting tricyclic carbon skeleton and are divided into two groups based on their shared structural characteristics. The pseudopterosin group possesses a tricyclic ring system containing an aromatic ring, while the amphilectane groups possesses a perhydrophenalene ring [13]. Amphilectanetype diterpenoids belonging to the pseudopterosin group such as pseudopterosins [11], helioporin E [14], and pseudopteroxazole [15] generally possess a fully substituted benzene ring and an isobutenyl group. In addition, most compounds of this class were isolated from marine invertebrates, as monoglycosylated forms with various biological activities such as anti-cancer, anti-malarial, and anti-inflammatory effects [11,13]. However, to the best of our knowledge, amphilectane-type diterpenoids with a tetrasubstituted benzene ring, as in 1, have not been reported yet. Therefore, compound 1 represents a new amphilectane-type diterpenoid of fungal origin possessing unique structural features.
The molecular formula of compound 2 (C 21 H 34 O 7 ) was determined on the basis of its HRESIMS and NMR data, indicating five units of unsaturation. Analysis of 1 H, 13 C, and DEPT NMR data of 2 (Table 2) indicated the presence of three methyl groups, six methylene units (two of which are oxygenated), eight sp 3 methines (six of which are oxygenated including one acetal), one sp 2 methine, and three quaternary carbons (one of which is sp 2 carbon). As only the resonances for a trisubstituted olefin (δ 121.5 and δ 141.2) were observed in the NMR data to account for unsaturation units, it was deduced that the compound must possess four rings to fulfill the required units of unsaturation. There were nine 1 H NMR signals in the region for oxygenated sp 3 hydrogens. This observation, together with five sp 3 oxygenated methines, including one acetal (δ 95.4, δ 75.6, δ 74.5 δ 74.1 and δ 72.1) and one oxygenated methylene (δ 62.9) signal in the 13 C NMR spectrum, were suggestive of a hexose moiety. This was also supported by contiguous COSY correlations of five oxymethines and one oxymethylene. Further chemical shift considerations and analysis of coupling constants among respective oxymethines (Table 2), along with the HMBC correlation of H-1 with C-5 confirmed the presence of a glucopyranose unit in the molecule. Moreover, it was indicated that the aglycone of 2 must possess no exchangeable hydrogens because the glucose unit accounts for all the exchangeable hydrogens required by the molecular formula. Further structural elucidation of the aglycone of 2 was carried out by analysis of COSY, HMQC, and HMBC data. Detailed analysis of COSY and HMBC data confirmed the presence of a glucopyranose ring moiety in the molecule. Spin systems consisting of H-1- were connected via C-8 and C-9 linkage by HMBC correlation from H 3 -15 with C-9, and this unit was further extended to form a cyclohexene ring system on the basis of the HMBC correlations of H 2 -9 and H-7 with C-5. Furthermore, HMBC correlations of H-1 with C-6, H 2 -10 with C-4, and H-6 with C-1 supported the spiro-connection between the aforementioned cyclopentane and cyclohexene moieties, with C-5 being the spiro center. HMBC correlations from the singlet signal H 3 -13 with C-1, C-11, and C-12 led to the connection of the methyl group C-13 to the quaternary carbon C-11 and a connection between C-1 and C-11. Finally, HMBC correlations of H 2 -12 with C-1, C-6, and C-11 led to the assignment of the tetrahydropyran ring moiety in the molecule. Taken together, the aglycone moiety of 2 was assigned to a spiro [4.5]decane system with an additional six-membered ether ring, and the glucopyranose unit was located at C-11 based on the HMBC correlation of the anomeric proton H-1 with C-11, thus completing the planar structure of 2 as shown. correlation of the anomeric proton H-1′ with C-11, thus completing the planar structure of 2 as shown. The relative configuration of the aglycone moiety of 2 was proposed based on the analysis of NOESY correlations (Figure 4). The signal for H-1 correlated with H-6, H3-13, and H3-14, placing them on the same face of the molecule. Furthermore, NOESY crosspeaks between H-6 and H3-14 supported this assignment. Therefore, the relative configuration of 1 for the aglycone portion of the molecule was established as shown. The glucose unit was assigned to be connected through an α-linkage based on the coupling constant (J = 3.6 Hz) of the anomeric proton (δ 5.57). To address the absolute configuration of the glucose unit in the molecule, HPLC analysis of the diastereomeric thiocarbamoyl-thiazolidine derivatives was performed [16]. In this analysis, compound 1 was hydrolyzed by heating in 2 M HCl and neutralized with NH4OH. After drying in vacuo, the residue was dissolved in pyridine and derivatized with L-cysteine methyl ester and phenyl isothiocyanate, as described in the Experimental section. Direct HPLC analysis of the reaction mixture exhibited the peak with a retention time at 38.0 min, corresponding to that of the thiocarbamoyl-thiazolidine derivative of D-glucose (Supplementary Materials, Figure  S26). As the anomeric carbon C-1′ is connected to C-11 via ether linkage, and there is free rotation around this bond, the absolute configuration of the aglycone moiety of the molecule could not be assigned with confidence.
The aglycone structure of 2 has the same carbon skeleton as cordycepol A, which was reported as an unusual spiro [4.5]decane sesquiterpene (acorane skeleton) with an additional pyran ring system [17]. Hence, the originally proposed relative configurations at C-1 and C-12 of cordycepol A have been revised [18]. However, the relative configurations of C-1, C-5, and C-6 in compound 2 neither matched with those in the originally proposed nor of revised cordycepol A. In addition, glycosylated cordycepol A has not been reported to date. Therefore, compound 2 was identified as a unique acorane-type sesquiterpene, and it was named isocordycepoloside A.
To evaluate the biological effects of the compounds isolated in this study, the inhibitory effects against PTP1B activity were investigated. PTP1B has been recognized as a key negative regulator of insulin and leptin pathways and thus has become a new drug target for the treatment of type 2 diabetes mellitus and obesity [19]. In an enzymatic assay using a p-nitrophenol phosphate (pNPP) as an enzyme substrate, compounds 1 and [D-Leu]ternatin (4) inhibited the PTP1B activity in a dose-dependent manner with IC50 values of 22.8 ± 1.1 μM and 14.8 ± 0.3 μM, respectively. The inhibitory effects of the remaining compounds were less pronounced, displaying 12-44% inhibition rates at a concentration of 80 for the connection between C-12 and the only remaining connection site C-1. Therefore, the tricyclic planar structure of 1 was assigned as shown to possess a hexahydro-1Hphenalene ring system. The carbons in compound 1 were numbered according to the precedent pseudopterosins [11]. The structure of 1 is recognized as a new amphilectane-type diterpenoid [12,13], and the name acrepseudoterin is proposed for compound 1.  The relative and absolute configuration of 1 was determined by analyzing the NO-ESY data ( Figure 2) and electron circular dichroism (ECD) calculations (Figure 3). The NOESY spectrum of 1 showed correlations of H-4 with H-1 and H-7, indicating that these protons are positioned on the same face of the ring system. On the other hand, NOESY correlations of H-5α with H3-18 and H3-19 demonstrated the placement of these methyl ) and NOESY ( for the connection between C-12 and the only remaining connection site C-1. Therefore, the tricyclic planar structure of 1 was assigned as shown to possess a hexahydro-1Hphenalene ring system. The carbons in compound 1 were numbered according to the precedent pseudopterosins [11]. The structure of 1 is recognized as a new amphilectane-type diterpenoid [12,13], and the name acrepseudoterin is proposed for compound 1.  The relative and absolute configuration of 1 was determined by analyzing the NO-ESY data ( Figure 2) and electron circular dichroism (ECD) calculations (Figure 3). The NOESY spectrum of 1 showed correlations of H-4 with H-1 and H-7, indicating that these protons are positioned on the same face of the ring system. On the other hand, NOESY correlations of H-5α with H3-18 and H3-19 demonstrated the placement of these methyl ) correlations for 2. The energy-minimized 3D structure was obtained by Macromodel (Version 12.5, Schrodinger LLC) program.
The relative configuration of the aglycone moiety of 2 was proposed based on the analysis of NOESY correlations (Figure 4). The signal for H-1 correlated with H-6, H 3 -13, and H 3 -14, placing them on the same face of the molecule. Furthermore, NOESY cross-peaks between H-6 and H 3 -14 supported this assignment. Therefore, the relative configuration of 1 for the aglycone portion of the molecule was established as shown. The glucose unit was assigned to be connected through an α-linkage based on the coupling constant (J = 3.6 Hz) of the anomeric proton (δ 5.57). To address the absolute configuration of the glucose unit in the molecule, HPLC analysis of the diastereomeric thiocarbamoyl-thiazolidine derivatives was performed [16]. In this analysis, compound 1 was hydrolyzed by heating in 2 M HCl and neutralized with NH 4 OH. After drying in vacuo, the residue was dissolved in pyridine and derivatized with L-cysteine methyl ester and phenyl isothiocyanate, as described in the Experimental section. Direct HPLC analysis of the reaction mixture exhibited the peak with a retention time at 38.0 min, corresponding to that of the thiocarbamoyl-thiazolidine derivative of D-glucose (Supplementary Materials Figure S26). As the anomeric carbon C-1 is connected to C-11 via ether linkage, and there is free rotation around this bond, the absolute configuration of the aglycone moiety of the molecule could not be assigned with confidence.
The aglycone structure of 2 has the same carbon skeleton as cordycepol A, which was reported as an unusual spiro [4.5]decane sesquiterpene (acorane skeleton) with an additional pyran ring system [17]. Hence, the originally proposed relative configurations at C-1 and C-12 of cordycepol A have been revised [18]. However, the relative configurations of C-1, C-5, and C-6 in compound 2 neither matched with those in the originally proposed nor of revised cordycepol A. In addition, glycosylated cordycepol A has not been reported to date. Therefore, compound 2 was identified as a unique acorane-type sesquiterpene, and it was named isocordycepoloside A.
To evaluate the biological effects of the compounds isolated in this study, the inhibitory effects against PTP1B activity were investigated. PTP1B has been recognized as a key negative regulator of insulin and leptin pathways and thus has become a new drug target for the treatment of type 2 diabetes mellitus and obesity [19]. In an enzymatic assay using a p-nitrophenol phosphate (pNPP) as an enzyme substrate, compounds 1 and [D-Leu]ternatin (4) inhibited the PTP1B activity in a dose-dependent manner with IC 50 values of 22.8 ± 1.1 µM and 14.8 ± 0.3 µM, respectively. The inhibitory effects of the remaining compounds were less pronounced, displaying 12-44% inhibition rates at a concentration of 80 µM. In this assay, ursolic acid (IC 50 = 3.8 ± 0.5 µM) was employed as the positive control. Following this, we investigated the effect of compound 1 on the kinetic profile of PTP1B-catalyzed pNPP hydrolysis. PTP1B was incubated with different concentrations of p-NPP in the absence or presence of compound 1. The assay was performed using the same method as the PTP1B assay, and the full velocity curves were determined. Kinetic analysis revealed that the inhibition mode of compound 1 was a competitive mode as the Lineweaver-Burk plot showed an increase in K m , without changing the V max value ( Figure 5). This result indicates that compound 1 might bind to the active site within PTP1B. μM. In this assay, ursolic acid (IC50 = 3.8 ± 0.5 μM) was employed as the positive control. Following this, we investigated the effect of compound 1 on the kinetic profile of PTP1Bcatalyzed pNPP hydrolysis. PTP1B was incubated with different concentrations of p-NPP in the absence or presence of compound 1. The assay was performed using the same method as the PTP1B assay, and the full velocity curves were determined. Kinetic analysis revealed that the inhibition mode of compound 1 was a competitive mode as the Lineweaver-Burk plot showed an increase in Km, without changing the Vmax value ( Figure 5). This result indicates that compound 1 might bind to the active site within PTP1B.

Specimen Collection and Identification
The fungal strain Acremonium sp. SF-7394 was isolated from an unidentified lichen collected from the Marian Cove (S 62°13′09.16″, W 58°45′57.67″) on King George Island, Antarctica in January, 2017. Voucher specimens (SF-7394) have been deposited in the Korea Polar Research Institute. One gram of the sample was mixed with sterile seawater (10 mL), and a portion (0.1 mL) of the sample was processed according to the spread plate method in potato dextrose agar (PDA) medium containing sterile seawater. The isolates

Conclusions
In this study, two new terpenoid-type fungal metabolites named acrepseudoterin (1) and isocordycepoloside A (2) were isolated from extracts of the Antarctic lichen-derived fungal strain Acremonium sp. SF-7394 along with three previously described fungal metabolites. The structure elucidation of these fungal metabolites was carried out mainly by analysis of their NMR and MS data, and the absolute configurations of 1 and 2 were assigned by electronic circular dichroism calculations and a chemical method. In the biological evaluation of these metabolites, acrepseudoterin (1) and [D-Leu]-ternatin (4) were identified as mild inhibitors of protein tyrosine phosphatase 1B (PTP1B), which is considered as the drug target for the treatment of type 2 diabetes mellitus and obesity. Taken together, this study supports the hypothesis that the fungal metabolites from extreme environments including the Antarctic area could serve as valuable resources for biologically active compounds with novel structures [20].