Hemiacetalmeroterpenoids A-C and Astellolide Q with Antimicrobial Activity from the Marine-Derived Fungus Penicillium sp. N-5.

Four new compounds including three andrastin-type meroterpenoids hemiacetalmeroterpenoids A-C (1-3), and a drimane sesquiterpenoid astellolide Q (15), together with eleven known compounds (4-14) were isolated from the cultures of the marine-derived fungus Penicillium sp. N-5, while compound 14 was first isolated from a natural source. The structures of the new compounds were determined by analysis of detailed spectroscopic data, and the absolute configurations were further decided by a comparison of the experimental and calculated ECD spectra. Hemiacetalmeroterpenoid A (1) possesses a unique and highly congested 6,6,6,6,5,5-hexa-cyclic skeleton. Moreover, the absolute configuration of compound 14 was also reported for the first time. Compounds 1, 5 and 10 exhibited significant antimicrobial activities against Penicillium italicum and Colletrichum gloeosporioides with MIC values ranging from 1.56 to 6.25 μg/mL.

1. Introduction

Andrastins are meroterpenoids characterized by a 6,6,6,5-tetra-carbocyclic skeleton. They are biogenetically derived from 3,5-dimethylorsellinic acid (DMOA) and farnesyl diphosphate (FPP), synthesized via a mixed polyketide-terpenoid pathway, and usually possess a keto-enol tautomerism at the cyclopentane ring [1,2,3,4]. To date, over 40 andrastins have been reported with multiple potential biological activities, including cytotoxic [5], anti-inflammatory [6], antiproliferative [7] and antimicrobial activity [4]. The complex structures and potential biological activities of andrastins have attracted much attention in recent years [8,9,10].

Marine fungus is known to be a natural source of structurally diverse and biologically active metabolites for drug discovery [11,12,13,14,15,16]. Recently, a series of novel bioactive natural products from marine fungi were reported by our group [17,18,19,20,21,22]. In our ongoing search for new bioactive secondary metabolites from marine fungi, the fungus Penicillium sp. N-5, isolated from the rhizosphere soil of mangrove plant Avicennia marina, led to the isolation of four new compounds, hemiacetalmeroterpenoids A–C (1–3) and astellolide Q (15). Especially, hemiacetalmeroterpenoid A (1) was a new andrastin-type meroterpenoid containing a unique 6,6,6,6,5,5-hexa-cyclic skeleton. Meanwhile, eleven known compounds, including 3-deacetyl-citreohybridonol (4) [23] citreohybridone A (5) [24], 3,5-dimethylorsellinic acid-based meroterpenoid 2 (6) [5], andrastins A–C (7, 10, 13) [25], andrastone C (8) [26], penimeroterpenoid A (9) [4], 23-deoxocitreohybridonol (11) [1], 6α-hydroxyandrastin B (12) [1], and compound V (14) [27] were also obtained from the fungus N-5 (Figure 1). All the isolated compounds were investigated for their antimicrobial activity against two phytopathogenic fungi and four bacterial strains. Herein, we report the isolation, structural characterization and antibacterial activity of these compounds.

Figure 1

Structure of compounds 1–15.

2. Results

2.1. Structure Identification

Hemiacetalmeroterpenoid A (1) was obtained as a white powder. It molecular formula was assigned as C26H34O7 according to HRESIMS analysis at m/z 459.23709 [M+H]+ (calcd. 459.23773), indicating ten degrees of unsaturation. In the 1H NMR spectrum, the signal for one olefinic proton (δH 5.63), one methoxyl (δH 3.60), one methine (δH 1.47), four methylenes (δH 1.42, 1.62, 1.85, 1.91, 1.94, 2.11, 2.33 and 2.61) and six methyls (δH 1.03, 1.07, 1.19, 1.23, 1.33 and 1.49). The 13C NMR data exhibited 26 carbon resonances, including two olefinic carbons for one double bond (δC 127.2, 150.1), three carbonyl carbons for two ketone (δC 203.7 and 203.8), and one ester carbonyl (δC 169.3), one methine (δC 49.1), five methylenes (one oxygenated), seven methyls (one oxygenated), eight quaternary carbons (one highly oxygenated: δC 99.8) (Table 1). The NMR data established a nucleus of meroterpenoid characterized by an andrastin scaffold, structurally similar to the citreohybriddione C (Figures S2 and S3) [28]. Analysis of the 1H-1H COSY data led to the identification of two isolated spin-systems of C-1/C-2 and C-5/C-6/C-7. The HMBC from H2-1 to C-3, C-10, from H1-5 to C-10, and from H3-22 to C-3, C-4, C-5, C-23, ring A was formed. The HMBC correlations from H3-24 to C-7, C-8, C-9, from H1-11 to C-8, C-10 and from H2-21 to C-5, C-10 completed ring B. Then, the HMBC cross-peaks from H2-1, H2-6 to C-10 and from H3-23, H2-7 to C-5 indicated ring A and ring B were fused at C-5 and C-10. Then, HMBC correlations from H3-24 to C-14, C-15, from H3-20 to C-11, C-12, C-13, C-17, from H3-19 to C-12, C-13, C-14, C-17 and from H3-18 to C-15, C-16, C-17, ring C and ring D were constituted, and they were blended at C-13 and C-14. The HMBC correlations from H2-6, H1-11 to C-8, from H1-11 to C-10, suggested ring B and ring C were tightly connected. In addition, the HMBC correlation from H3-26 to C-25 implied the presence of a methyl carboxylate. A weak HMBC correlation from H3-26 to C-14 located the methyl carboxylate at C-14. Except one double bond, three carbonyls and four rings, ten degrees of unsaturation indicated that two new rings were required. According to the HMBC correlation from H2-21 to C-3 (δC 99.8), a 6-membered ring was confirmed between C-1, C-2, C-3, C-10, and C-21. Finally, another new 5-membered ring was formed by intramolecular dehydration of hydroxyl groups at C-12 and C-16. Thus, the planar structure of 1 was established as shown in Figure 2.

Table 1

1H NMR (600 MHz) and 13C NMR (150 MHz) of 1-3 in CD3OD.

Position	1		2		3
	δ C	δH (J in Hz)	δ C	δH (J in Hz)	δ C	δH (J in Hz)
1	34.7 (CH2)	1.42, m2.33, m	35.3 (CH2)	1.12, m2.19, m	34.8 (CH2)	1.15, m2.20, m
2	30.2 (CH2)	1.85, m2.16, m	30.3 (CH2)	1.74, m2.12, m	30.1 (CH2)	1.76, m2.14, m
3	99.8 (C)		99.5 (C)		99.5 (C)
4	41.4 (C)		41.3 (C)		41.3 (C)
5	49.1 (CH)	1.47, m	50.9 (CH)	1.33, m	51.4 (CH)	1.21, m
6	19.4 (CH2)	1.62, m1.91, m	20.5 (CH2)	1.55, m1.75, m	20.4 (CH2)	1.62, m1.81, m
7	32.3 (CH2)	1.94, m2.61, m	32.5 (CH2)	2.07, m2.76, m	32.9 (CH2)	1.94, m2.23, m
8	40.2 (C)		42.4 (C)		41.9 (C)
9	150.1 (C)		48.5 (CH)	1.89, t (2.7)	48.6 (CH)	1.98, t (2.7)
10	38.5 (C)		36.3 (C)		36.3 (C)
11	127.2 (CH)	5.63, s	124.2 (CH)	5.42, m	126.0 (CH)	5.60, m
12	77.4 (C)		137.7 (C)		133.7 (C)
13	54.4 (C)		57.5 (C)		60.6 (C)
14	73.4 (C)		69.7 (C)		69.2 (C)
15	203.7 (C)		190.7 (C)		171.9 (C)
16	76.7 (C)		113.5 (C)		131.9 (C)
17	203.8 (C)		201.4 (C)		202.1 (C)
18	7.9 (CH3)	1.19, s	6.6 (CH3)	1.57, s	8.8 (CH3)	1.55, s
19	11.0 (CH3)	1.33, s	18.0 (CH3)	1.18, s	17.4 (CH3)	1.20, s
20	24.2 (CH3)	1.23, s	20.2 (CH3)	1.82, s	19.1 (CH3)	1.75, s
21	74.4 (CH2)	3.55, d (7.6)4.39, d (8.7)	68.6 (CH2)	3.81, d (9.0)4.22, d (9.0)	68.5 (CH2)	3.82, d (8.9)4.21, d (9.0)
22	27.2 (CH3)	1.07, s	27.9 (CH3)	1.04, s	27.9 (CH3)	1.07, s
23	18.9 (CH3)	1.04, s	18.9 (CH3)	1.01, s	18.8 (CH3)	1.03, s
24	25.9 (CH3)	1.49, s	16.7 (CH3)	1.19, s	16.5 (CH3)	1.24, s
25	169.3 (C)		172.6 (C)		170.9 (C)
26	52.5 (CH3)	3.60, s	51.9 (CH3)	3.56,s	52.4 (CH3)	3.59,s
Ac-CH3					21.2 (CH3)	2.36, s
Ac-OCO					167.3 (C)

Figure 2

Key HMBC and COSY correlations of 1–3 and 15.

The relative configuration of compound 1 was defined by the NOESY correlations. The correlations of H2-21 with H3-23, H3-20 with H3-19, H3-24, and H3-18 with H3-19, H3-26 were observed in the NOESY spectrum, which means H3-18, H3-19, H3-20, H2-21, H3-23, H3-24 and H3-26 were on the same side. The NOESY correlations of H1-5 with H3-22 suggested that H1-5 and H3-22 were in the opposite face (Figure 3). The absolute configuration of 1 was determined by comparing the calculated ECD spectra generated by the time-dependent density functional theory (TDDFT) for two enantiomers 3R, 5S, 8S, 10S, 12R, 13S, 14R, 16R-1a and 3S, 5R, 8R, 10R, 12S, 13R, 14S, 16S-1b with the experimental one. Finally, the experimental ECD spectrum of 1 was nearly identical to the calculated ECD spectrum for 1a (Figure 4), clearly suggesting the 3R, 5S, 8S, 10S, 12R, 13S, 14R, 16R absolute configuration for 1.

Figure 3

Key NOE correlations of 1–3 and 14–15.

Figure 4

ECD spectra of compounds 1 (A), 2 and 3 (B), 14 and 15 (C) in CH3OH.

Hemiacetalmeroterpenoid B (2) was isolated as a white powder and had a molecular formula of C26H36O6, determined by HRESIMS data m/z 445.25772 [M+H]+ (calcd. 445.25847) with nine degrees of unsaturation. The 1H NMR spectrum of 2 displayed the signal for one olefinic proton (δH 5.42), one methoxyl (δH 3.56), two methines (δH 1.33 and 1.89), four methylenes (δH 1.12, 1.33, 1.55, 1.75, 2.07, 2.12, 2.19 and 2.76) and six methyls (δH 1.01, 1.04, 1.18, 1.19, 1.57 and 1.82). The 13C NMR data revealed 26 carbon resonances, involving four olefinic carbons for two double bonds (δC 113.5, 124.2, 137.7, 190.7), two carbonyl carbons for one ketone (δC 201.4), one ester carbonyl (δC 172.6) (Table 1). According to 1D NMR and 2D NMR data, the planar structure of 2 was similar to the co-isolated andrastin B (13). The obvious difference is that the acetyl group at the C-3 position of compound 2 disappears. Meanwhile, the HMBC from H2-21 to C-3 (δC 99.5) also indicated that a new 6-membered ring was formed between C-1, C-2, C-3, C-10 and C-21 (Figure 2).

The NOESY spectrum indicated that H1-5, H1-9 and H3-22 were on the same side based on the correlations of H1-5 with H1-9 and H3-22. On the contrary, it was suggested that H3-19, H3-21, H3-23, H3-24, and H3-26 were on the other side based on the NOESY correlations of H2-21 with H3-23 and H3-24, along with H3-19 with H3-24 and H3-26 (Figure 3). Thus, the relative configuration of 2 was determined to be 3R, 5S, 8S, 9R, 10S, 13R and 14R. The absolute configuration of the stereogenic centers in 2 was assigned as 3R, 5S, 8S, 9R, 10S, 13R and 14R by comparing its experimental ECD spectrum with that of the calculated model molecule (Figure 4).

Hemiacetalmeroterpenoid C (3) was also purified as a white powder. The molecular formula was specified as C28H38O7 (ten degrees of unsaturation) by HRESIMS (m/z 509.25015 [M+Na]+), which is 42 mass units higher than that of 2 (Figure S17). Analysis of its NMR data (Table 1) revealed the presence of the same partial structure as that found in compound 2. The only difference was 3 has an additional acetyl fragment. Finally, a weak HMBC correlation from Ac-CH3 to C-15 suggested that the acetyl fragment was attached to C-15 (Figure 2).

Because compound 3 has the same chiral center as 2, the NOESY correlation and experimental ECD spectrum of compound 3 were in agreement with those of 2 (Figure 3 and Figure 4). Thus, the absolute configuration of 3 was identified as 3R, 5S, 8S, 9R, 10S, 13R and 14R.

Compound 14 was obtained as a yellow powder. Analysis of its 1H NMR and 13C NMR data showed that the planar structure of 14 was the same as compound V, which was the product of the alkaline hydrolysis of parasiticolide A [27]. However, the absolute configuration of compound V was ambiguous.

The relative configuration of 14 was also defined by the NOESY correlation. The correlations of H3-14 with H1-5 and H1-6, and H2-13 with H2-15 were found in the NOESY spectrum, which means H1-5, H1-6, and H3-4 were on the same side, and H2-13 and H2-15 were on the opposite face (Figure 3). Thus, the absolute configuration of the stereogenic centers in 14 was assigned as 4R, 5R, 6S, 10S by comparing its experimental ECD spectrum with that of the calculated model molecule (Figure 4). Finally, compound 14 was named as astellolide J.

Astellolide Q (15) was also acquired as a yellow powder. It molecular formula was determined as C17H24O6 according to HRESIMS analysis at m/z 347.14578 [M+Na]+ (calcd. 347.14651), indicating six degrees of unsaturation. The 1H NMR of 15 showed two methyls (δH 1.15 and 2.08), four methylenes (δH 1.16, 1.45, 1.54, 1.78, 1.91, 2.05, 2.34 and 2.50), one methines (δH 1.74) one hydroxymethine (δH 4.55) and three hydroxy-methylenes (δH 3.34, 3.92, 4.09, 4.33, 4.84 and 5.04). In addition, according to the HSQC data, the 13C NMR data showed the presence of 17 carbon signals, including two ester carbonyl carbons (δC 173.1, 177.0) and two olefinic carbons (δC 124.0, 169.0), one methyl, seven methylenes (three oxygenated), two methines (one oxygenated), two aliphatic quaternary carbons (Table 2). Analysis of its 1H NMR and 13C NMR data in association with the 2D NMR data established a nucleus of drimane sesquiterpenoid characterized by an astellolide scaffold, structurally similar to the co-isolated compound 14 (Figures S26 and S27). It can be clearly observed that compound 15 has an additional acetyl fragment. Furthermore, the HMBC from H2-13 to Ac-OCO indicated that the acetyl fragment was linked to C-13 (Figure 3).

Table 2

1H NMR (400 MHz) and 13C NMR (100 MHz) of 15 in CD3OD.

Position	δ C	δH (J in Hz)	Position	δ C	δH (J in Hz)
1	35.3 (CH2)	1.45, m2.05, m	10	44.2 (C)
2	19.5 (CH2)	1.54, m1.78, m	11	71.8 (CH2)	5.00, d (17.7)4.84, d (17.6)
3	37.0 (CH2)	1.16, m1.91, m	12	177.0 (C)
4	39.3 (C)		13	68.1 (CH2)	4.44, d (11.2)4.62, d (5.4)
5	56.4 (CH)	1.74, s	14	28.1 (CH3)	1.16, s
6	63.6 (CH)	4.61, d (11.0)	15	65.7 (CH2)	3.76, d (12.0)4.33, d (11.9)
7	33.0 (CH2)	2.34, d, (18.9)2.50, d (18.3)	Ac-CH3	20.8 (CH3)	2.08, s
8	124.0 (C)		Ac-OCO	173.1 (C)
9	169.0 (C)

Finally, the NOESY correlation and experimental ECD spectrum of compound 15 were identical to those of 14 (Figure 3 and Figure 4). Thus, the absolute configuration of 15 was also assigned as 4R, 5R, 6S, 10S.

2.2. Antimicrobial Assay

Compounds 1–15 were investigated for their antimicrobial activities against two phytopathogenic fungi and four bacterial strains. As shown in Table 3, andrastin-type meroterpenoids have better antimicrobial activities against phytopathogenic fungus than against bacteria. Most of all the tested compounds (9 compounds out of total 15 compounds) displayed potent antimicrobial activities (MIC < 50 μg/mL). Among them, compounds 1, 5 and 10 exhibited remarkable antimicrobial activities against Penicillium italicum and Colletrichum gloeosporioides with MIC values of 6.25, 1.56, 6.25 and 6.25, 3.13, 6.25 μg/mL. Moreover, compound 1 showed inhibitory activities against Bacillus subtilis under concentration of 6.25 μg/mL. Compound 10 also displayed significant antimicrobial activity against Salmonella typhimurium with an MIC value of 3.13 μg/mL. Notably, compound 5 revealed potential antimicrobial activity against all the strains, the MIC values were lower than 25 μg/mL.

Table 3

Antimicrobial activity of compounds 1–15.

	Microbia	Methicillin-Resistent Staphyococcus aureus (μg/mL) a	Bacillussubtilis (μg/mL) a	Pseudomonas aeruginosa (μg/mL) a	Salmonella typhimurium (μg/mL) a	Penicillium italicum(μg/mL) a	Colletrichum gloeosporioides (μg/mL) a
Compound
1		25	6.25	>50	>50	6.25	6.25
2		>50	>50	25	>50	50	>50
3		>50	>50	>50	>50	50	>50
4		>50	>50	>50	>50	>50	>50
5		50	25	25	>50	1.56	3.13
6		>50	25	50	>50	12.50	25
7		>50	>50	>50	>50	25	25
8		>50	>50	>50	>50	>50	>50
9		>50	>50	>50	>50	>50	>50
10		25	12.50	25	3.13	6.25	6.25
11		>50	>50	>50	>50	>50	>50
12		>50	>50	>50	>50	>50	>50
13		50	>50	>50	>50	50	>50
14		>50	>50	>50	>50	>50	>50
15		>50	>50	>50	>50	25	25
Ampicillin		0.13	0.13	0.07	0.13	-	-
Ketoconazole		-	-	-	-	0.78	0.78

a: The deviation value of three parallel experiments; -: No test.

As for the study of the structure–activity relationship (SAR), it was found that the degree of oxidation at C-21 had different effects on the activities of the compounds. The compound with methyl (10) at C-21 has significantly antimicrobial activity, followed by the aldehyde group (7), and hydroxymethyl (13) was the weakest. In-depth analysis showed that apart from the degree of oxidation at C-21, keto-enol tautomerism at the cyclopentane ring also had obvious influences on the antimicrobial activities of compounds. Compared to compounds 7 and 13 (enol form), compounds 8 and 9 (keto form) showed no activities against all strains (Table 3).

3. Experimental Methods

3.1. General Experimental Procedures

The NMR were tested on a Bruker Avance 600 MHz spectrometer (Karlsruhe, Germany) at room temperature. Optical rotations data were recorded on an MCP300 (Anton Paar, Shanghai, China). UV were tested using a Shimadzu UV-2600 spectrophotometer (Shimadzu, Kyoto, Japan). IR spectra were recorded on IR Affinity-1 spectrometer (Shimadzu, Kyoto, Japan). HR-ESI-MS spectra were tested on a ThermoFisher LTQ-Orbitrap-LC-MS spectrometer (Palo Alto, CA, USA). LC-MS/MS data was performed on a Q-TOF manufactured by Waters and a Waters Acquity UPLC BEH C18 column (1.7 µm, 2.1 × 100 mm). Recoated silica gel plates (Qingdao Huang Hai Chemical Group Co., Qingdao, China, G60, F-254), Column chromatography (CC) and Sephadex LH-20 (Amersham Pharmacia, Stockholm, Sweden) were used to purify the compounds.

3.2. Fungal Material

Fungus N-5 was isolated from the rhizosphere soil of mangrove plant Avicennia marina (collected in October 2021 from Nansha Mangrove National Nature Reserve in Guangdong Province, China). It was identified as Penicillum sp. by the ITS region (deposited in GenBank, accession no ON926808), and fungus N-5 was deposited at Sun Yat-sen University, China.

3.3. Fermentation

The fungus Penicillum sp. N-5 was cultured in one hundred 1000 mL Erlenmeyer flasks at 25 °C for 30 days; these contained autoclaved rice solid-substrate medium composed of 50 g rice and 50 mL 3‰ saline water.

3.4. Extraction and Purification

After incubation, the mycelia and solid rice medium were extracted four times with EtOAc, and 75 g of residue was obtained. Next, the residue was separated by a gradient of petroleum ether/EtOAc from 9:1 to 0:10 (v/v) on silica gel CC and divided into six fractions (Fr.1–Fr.6). Fr. 2 (10 g) was separated to Sephadex LH-20 (methanol) to yield three sub-fractions (SFrs. 2.1–2.3). SFrs.2.3 (1.2 g) was applied to silica gel CC (DCM/MeOH v/v, 100:1) and further purified by reversed-phase (RP) high performance liquid chromatography (HPLC; 90–10% MeCN/H2O for 25 min) to obtain compounds 1 (5 mg) and 3 (7 mg). Fr. 3 (16 g) was also separated to Sephadex LH-20 (methanol) to yield four sub-fractions (SFrs. 3.1–3.4). SFrs.3.1 (1.6 g) was separated to silica gel CC (DCM/MeOH v/v, 80:1) and further purified by reversed-phase (RP) high performance liquid chromatography (HPLC; 75–25% MeCN/H2O for 22 min) to yield compounds 2 (11 mg) and 15 (6 mg).

Hemiacetalmeroterpenoid A (1): white powder, m.p. 122.8–124.1 °C; -52 (c 0.02, MeOH), UV (MeOH) λmax (log ε): 206 (2.52) (Figure S33); ECD (MeOH) λmax (∆ε): 240 (+5.47), 301 (−1.14), 362 (+0.61); 1H (600 MHz, CD3OD) and 13C NMR (150 MHz, CD3OD) data, see Table 1; HR-ESI-MS: m/z 459.23709 [M+H]+ (calcd. for C26H35O7, 459.23773).

Hemiacetalmeroterpenoid B (2): white powder, m.p. 106.9–108.4 °C; −56 (c 0.02, MeOH), UV (MeOH) λmax (log ε): 205 (2.83), 238 (1.36) (Figure S34); ECD (MeOH) λmax (∆ε): 206 (−11.92), 248 (+3.38), 311 (−1.19); 1H (600 MHz, CD3OD) and 13C NMR (150 MHz, CD3OD) data, see Table 1; HR-ESI-MS: m/z 445.25772 [M+H]+ (calcd. for C26H37O6, 445.25847).

Hemiacetalmeroterpenoid C (3): white powder, m.p. 100.8–102.6 °C; −66 (c 0.02, MeOH), UV (MeOH) λmax (log ε): 205 (2.51), 260 (1.78) (Figure S35); ECD (MeOH) λmax (∆ε): 206 (−18.31), 240 (+12.72), 310 (−2.18); 1H (600 MHz, CD3OD) and 13C NMR (150 MHz, CD3OD) data, see Table 1; HR-ESI-MS: m/z 509.25015 [M+Na]+ (calcd. for C28H38O7Na, 509.25097).

Astellolide J (14): yellow powder, m.p. 202.9–204.5 °C; +16 (c 0.02, MeOH), UV (MeOH) λmax (log ε): 216 (3.15) (Figure S36); ECD (MeOH) λmax (∆ε): 203 (−1.82), 225 (+3.27); 1H (400 MHz, CD3OD) and 13C NMR (100 MHz, CD3OD) data; HR-ESI-MS: m/z 305.13565 [M+Na]+ (calcd. for C15H22O5Na, 305.13594).

Astellolide Q (15): yellow powder, m.p. 160.1–162.2 °C; +12 (c 0.02, MeOH), UV (MeOH) λmax (log ε): 218 (3.62) (Figure S37); ECD (MeOH) λmax (∆ε): 232 (+5.19); 1H (400 MHz, CD3OD) and 13C NMR (100 MHz, CD3OD) data, see Table 2; HR-ESI-MS: m/z 347.14578 [M+Na]+ (calcd. for C17H24O6Na, 347.14578).

3.5. ECD Calculation

Firstly, ECD calculations of compounds 1–3 and 14–15 were performed by the Gaussian 09 program and Spartan’14. Next, the conformations with a Boltzmann population (>5%) were selected for optimization and calculation in methanol at B3LYP/6-31+G (d, p). Finally, the ECD spectra were generated by the program SpecDis 1.6 (University of Würzburg, Würzburg, Germany) and drawn by OriginPro 8.0 (OriginLab, Ltd., Northampton, MA, USA) from dipole-length rotational strengths by applying Gaussian band shapes with sigma = 0.30 eV [29,30].

3.6. Bioassays Antimicrobial Activity

Antimicrobial activity assay was performed as previously described in [31,32].

4. Conclusions

In summary, three new andrastin-type meroterpenoids (1–3), one new drimane sesquiterpenoid (15) and one sesquiterpenoid J (14) that was first isolated from a natural source, together with ten known compounds (4–13) were isolated from the cultures of the rhizosphere soil of mangrove plant Avicennia marina fungus Penicillium sp. N-5. Their structures were determined by the analysis of NMR, HR-MS and ECD spectra. All the isolated compounds were investigated for their antimicrobial activities against two phytopathogenic fungi and four bacterial strains. Among them, compounds 1, 5 and 10 exhibited significant inhibition against Penicillium italicum and Colletrichum gloeosporioides with MIC values of 6.25, 1.56, 6.25 and 6.25, 3.13, 6.25 μg/mL. Notably, compound 5 showed potential antimicrobial activity against all the strains and the MIC values were lower than 25 μg/mL. Moreover, andrastin-type meroterpenoid antimicrobial activity against phytopathogenic fungi was reported for the first time.