Zosteropenillines: Polyketides from the Marine-Derived Fungus Penicillium thomii

1. Introduction

Marine-derived fungi are a prolific source of new secondary metabolites, many of which are biologically active [1,2,3]. In previously published works, we described the isolation and identification of 10 new meroterpenoids–austalides and seven new 6,6-spiroketals–sargassopenillines A–G from fungi Penicillium thomii and P. lividum associated with the brown alga Sargassum miyabei [4,5] and four new eudesmane-type sesquiterpenes–thomimarines A–D from P. thomii KMM 4667 associated with the sea grass Zostera marina [6]. Recently, we have isolated 11 new polyketides, pallidopenillines that have a polyketidic decalin scaffold from P. thomii associated with the brown alga Sargassum pallidum [7]. During our ongoing search for new natural compounds from marine-derived fungi, we investigated the strain P. thomii KMM 4674 isolated from the seagrass Z. marina. Herein, we report the isolation, structure elucidation and biological assay results of 12 new polyketides containing “decalin” motif produced by this fungus (Figure 1).

2. Results and Discussion

2.1. Structure Elucidation

The molecular formula of 1 was established to be C₁₅H₂₂O₃ from a HRESIMS peak at m/z 273.1461 [M + Na]⁺ and by ¹³C NMR analyses. A close inspection of ¹H NMR, ¹³C NMR, DEPT, and HSQC data of 1 (

Table 1. ¹³C NMR spectroscopic data (δ in ppm) for zosteropenillines A–F (1–6).

Position	1 *	2 *	3 *	4 **	5 **	6 *
1	60.9, CH2	60.9, CH2	60.9, CH2	60.9, CH2	60.9, CH2	57.6, CH2
2	39.9, CH2	39.9, CH2	39.9, CH2	39.9, CH2	37.9, CH2	48.6, CH2
3	210.2, C	210.4, C	210.3, C	210.9, C	206.0, C	217.6, C
4	62.8, CH	62.9, CH	62.7, CH	63.0, CH	63.7, CH	61.8, CH
5	37.5, CH	39.5, CH	38.9, CH	39.3. CH	38.5, CH	37.4, CH
6	28.7, CH2	28.8, CH2	38.7, CH2	29.3, CH2	29.0, CH2	29.4, CH2
7	32.7, CH2	29.1, CH2	24.9, CH2	34.9, CH2	31.8, CH2	32.9, CH2
8	40.2, CH	40.5, CH	69.7, C	32.8, CH	39.2, CH	40.6, CH
9	77.9, CH	35.2, CH2	44.5, CH2	40.9, CH2	79.2, CH	77.8, CH
10	48.6, CH	41.4, CH	36.9, CH	41.9, CH	53.5, CH	49.1, CH
11	130.1, CH	134.4, CH	134.4, CH	130.5, CH	67.3, CH	128.6, CH
12	131.6, CH	130.9, CH	131.1, CH	134.8, CH	72.7, CH	133.0, CH
13	74.7, C	75.0, C	75.0, C	75.2, C	77.5, C	69.1, C
14	23.2, CH3	23.3, CH3	23.3, CH3	23.3, CH3	22.0, CH3	28.8, CH3
15	18.4, CH3	68.1, CH2	31.5, CH3	22.3, CH3	19.1, CH3	18.4, CH3

* Chemical shifts were measured at 125.77 MHz in CDCl₃; ** Chemical shifts were measured at 176.04 MHz in CDCl₃.

and

Table 2. ¹H NMR spectroscopic data (δ, J in Hz) for zosteropenillines A–F (1–6).

Position	1 **	2 *	3 *	4 **	5 **	6 *
1	a: 4.11, ddd (12.0, 8.0, 1.2) b: 3.89, td (12.0, 3.0)	a: 4.11, ddd (11.8, 8.0, 1.0) b: 3.89 td (12.0, 3.0)	a: 4.11, ddd (11.8, 8.0, 1.0) b: 3.89, td (12.0, 2.9)	a: 4.11, ddd (11.7, 8.0, 1.4) b: 3.89, td (12.0, 3.0)	a: 4.22, dd (12.0, 9.0) b: 3.91, td (12.0, 4.0)	a: 3.91, ddd (11.7, 6.2, 4.2) b: 3.87, ddd (11.7, 6.2, 4.2)
2	a: 2.64, ddd (14.0, 12.0, 8.0) b: 2.21, ddt (14.0, 3.0, 1.2)	a: 2.66, ddd (14.1, 12.1, 8.0) b: 2.21, ddt (14.1, 3.0, 1.3)	a: 2.66, ddd (14.0, 12.1, 8.0) b: 2.21, ddt (13.9, 2.9, 1.3)	a: 2.68, ddd (14.0, 12.0, 3.0) b: 2.21, ddt (14.0, 3.0, 1.5)	a: 2.67, ddd (15.0, 12.0, 9.0) b: 2.21, dd (15.0, 4.0)	a: 2.86, ddd (18.4, 6.2, 4.2) b: 2.76, ddd (18.4, 6.2, 4.4)
4	2.09, dd (11.8, 1.2)	2.07, dd (11.3, 1.2)	2.10, dd (11.3, 1.2)	2.04, dd (11.5, 1.6)	2.11, d (11.7)	2.59, d (11.4)
5	1.89, tdd (11.8, 10.6, 3.2)	1.78, m	1.75, m	1.75, m	1.95, m	1.93, tdd (11.4, 10.4, 3.0)
6	a: 1.28, m b: 1.14, qd (13.0, 3.3)	a: 1.41, dq (13.2, 3.2) b: 1.14, qd (13.2, 3.5)	a: 1.69, m b: 1.41, m	a: 1.34, dq (13.3, 3.6) b: 1.11, qd (13.0, 3.8)	a: 1.33, m b: 1.11, m	a: 1.50, m b: 1.15, qd (12.7, 3.2)
7	a: 1.78, dq (12.7, 3.3) b: 1.08, qd (12.7, 3.6)	a: 1.85, dq (12.9, 3.4) b: 1.01, qd (12.9, 3.7)	a: 1.45, m b: 1.19, m	a: 1.75, m b: 0.96, m	a: 1.73, m b: 1.03, m	a: 1.77, m b: 1.12, qd (13.0, 3.3)
8	1.41, m	1.63, m		1.48, m	1.48, m	1.42, m
9	2.92, td (9.9, 5.8)	a: 1.91, dq (12.6, 3.5) b: 0.93, q (12.3)	a: 1.75, m b: 1.28, m	a: 1.77, m b: 0.87, q (12.2)	3.29, t (9.0)	2.92, t (9.9)
10	1.65, tt (10.4, 2.3)	1.74, m	2.15, ddd (13.3, 10.2, 3.5)	1.71, m	1.61, td (10.8, 9.0)	1.73, tt (10.3, 2.3)
11	6.24, dd (10.0, 2.4)	5.67, dd (9.8, 1.5)	5.63, brs	5.59, dd (9.9, 2.5)	4.38, t (10.5)	6.11, dd (10.0, 2.0)
12	5.69, dd (10.0, 2.6)	5.61, dd (9.8, 2.5)	5.63, brs	5.65, dd (9.8, 1.0)	3.78, d (10.5)	5.64, dd (10.0, 2.6)
14	1.26, s	1.26, s	1.26, s	1.25, s	1.36, s	1.30, s
15	1.03, d (6.5)	a: 3.50, dd (10.3, 6.3) b: 3.47, dd (10.3, 6.3)	1.25, s	0.91, d (6.6)	1.06, d (6.5)	1.03, d (6.5)
9-OH	1.55, d (6.3)

* Chemical shifts were measured at 500.13 MHz in CDCl₃; ** Chemical shifts were measured at 700.13 MHz in CDCl₃.

) revealed the presence of two methyl (δ_H 1.26, δ_C 23.2 and δ_H 1.03, δ_C 18.4) groups, four methylenes (δ_C 39.9, 32.7, 28.7), including one oxygen-bearing (δ_H 4.11, 3.89, δ_C 60.9), and seven methines (δ_H 1.89, δ_C 37.5, δ_H 1.41, δ_C 40.2, δ_H 1.65, δ_C 48.6, δ_H 2.09, δ_C 62.8, δ_H 6.24, δ_C 130.1, δ_H 5.69, δ_C 131.6), together with one oxygen-bearing (δ_H 2.92, δ_C 77.9), one carbonyl carbon (δ_C 210.2), and one oxygenated quaternary carbon (δ_C 74.7). These data and five unsaturated degrees from the molecular formula suggested that compound 1 possessed three rings. COSY-45 data and HMBC correlations (Figure 2) from H-4 (δ_H 2.09) to C-5 (δ_C 37.5), C-10 (δ_C 48.6), C-14 (δ_C 23.2), from H-5 (δ_H 1.89) to C-4 (δ_C 62.8), C-6 (δ_C 28.7), C-10, C-13 (δ_C 74.7), from H₂-6 (δ_H 1.28, 1.14) to C-5, C-7 (δ_C 32.7), C-8 (δ_C 40.2) and C-10, from H-7a (δ_H 1.78) to C-5, C-6, C-8 and C-15 (δ_C 18.4), from H-7b (δ_H 1.08) to C-9 (δ_C 77.9), from H-8 (δ_H 1.41) to C-7, C-9 and C-10, from H₃-15 (δ_H 1.03) to C-7, C-8 and C-9, from H-9 (δ_H 2.92) to C-10, C-11 (δ_C 130.1), C-15, from H-10 (δ_H 1.65) to C-11, C-12 (δ_C 131.6), from H-11 (δ_H 6.24) to C-13, from H-12 (δ_H 5.69) to C-4, C-13, and C-14 revealed the presence of a decalin moiety and established a Δ¹¹ double bond and the location of methyl groups at C-8 and C-13 in 1.

HMBC correlations from H-1a (δ_H 4.11) to C-2 (δ_C 39.9), C-3 (δ_C 210.2) and C-13, from H-2a (δ_H 2.64) to C-1 (δ_C 60.9), C-3, from H-2b (δ_H 2.21) to C-3, C-4 established a saturated γ-pyrone derivative moiety in 1. NOESY cross-peaks H₃-14 (δ_H 1.26)/H-4 (δ_H 2.09), H-1β (δ_H 3.89); H₃-15 (δ_H 1.03)/H-9 (δ_H 2.92); H-5/H-2β (δ_H 2.64), H-6β (δ_H 1.28), H-7β (δ_H 1.08), H-9; H-10 (δ_H 1.65)/H-6α (δ_H 1.14), H-8 (δ_H 1.41), H-4; H-9/H₃-15, H-5 and H-4/H-6α, H-10, H₃-14 indicated a trans-ring fusion of the A and B rings, cis-ring fusion of the B and C rings, the α-orientation of H₃-14 and 9-OH, and the β-orientation of H₃-15. The planar structure and relative configuration of 1 were unequivocally confirmed by X-ray analysis, which was carried out for a single crystal obtained by recrystallization from acetonitrile–water (Figure 2 and Figure S9).

Esterification of 1 with (R)- and (S)-MTPA chloride occurred at the C-9 hydroxy group to give the (S)- and (R)-MTPA esters 1a and 1b, respectively. The observed chemical shift differences Δδ (δ_S − δ_R) (Figure 3) indicated the 9R configuration. These data and observed NOESY correlations determined the absolute stereostructure of 1 as 4R, 5S, 8S, 9R, 10R, and 13S. Compound 1 was named zosteropenilline A.

The molecular formula of 2 was established to be C₁₅H₂₂O₃ from a HRESIMS peak at m/z 273.1474 [M + Na]⁺ and by ¹³C NMR analyses. The general features of the ¹³C NMR of 2 resembled those of 1 with the exception of the C-9–C-11 and C-15 carbon signals. COSY and HSQC spectra of 2 revealed the partially connectivity sequence of the protons in the A ring as CH₂(15)-CH(8)-CH₂(9)-CH(10). These data and HMBC correlations from H-9b (δ_H 0.93) to C-7 (δ_C 29.1), C-8 (δ_C 40.5), C-10 (δ_C 41.4), C-11 (δ_C 134.4), and C-15 (δ_C 68.1); and from H₂-15 (δ_H 3.50, 3.47) to C-7, C-8 and C-9, established the A ring structure, lacking the hydroxy group at C-9, and indicated the presence of a hydroxymethyl group at C-8 in 2. The NOESY cross-peaks H-4 (δ_H 2.07)/H-10 (δ_H 1.74), H₃-14 (δ_H 1.26); H-8 (δ_H 1.63)/H-9α (δ_H 1.91), H-10; H-5 (δ_H 1.78)/H-9β (δ_H 0.93); H-9β/H₂-15 (δ_H 3.50, 3.47) indicated the trans-ring fusion of the A and B ring, cis-ring fusion of the B and C ring, and the β-orientation of hydroxymethyl group at C-8. Compound 2 was named zosteropenilline B.

The molecular formula of 3 was established to be C₁₅H₂₂O₃ from a HRESIMS peak at m/z 273.1463 [M + Na]⁺ and by ¹³C NMR analyses. The ¹H and ¹³C NMR spectra (Table 1 and Table 2) for this compound were very similar to those obtained for zosteropenilline B (2) with the exception of the C-6–C-10 and C-15 carbon and proton signals. The HMBC correlations H-9a (δ_H 1.75)/C-8 (δ_C 69.7), C-10 (δ_C 36.9); H₃-15 (δ_H 1.25)/C-7 (δ_C 24.9), C-8, C-9 (δ_C 44.5) established the structure of 3 including the hydroxy and methyl groups at the C-8 position. The relative configuration of 3 was defined based on the observed NOESY correlations (Figure S27). Compound 3 was named zosteropenilline C.

The molecular formula of 4 was established to be C₁₅H₂₂O₂ from a HRESIMS peak at m/z 257.1510 [M + Na]⁺ and by ¹³C NMR analyses. The ¹H and ¹³C NMR data (Table 1 and Table 2) observed for 4 closely resembled those obtained for zosteropenilline B (2) with the exception of the C-7–C-9 and C-15 carbon and proton signals. The mutual correlations from H₃-15 to C-7 and C-9 established the structure of the A ring and location methyl group at C-8. Compound 4 was named zosteropenilline D.

The absolute configurations of zosteropenillines B–D (2–4) were determined on the basis of the ECD spectroscopy data. The geometry of the stable conformations of compounds 1–4 were optimized using general procedure, described in the experimental section of the paper. The internal rotations of the hydroxyl groups as well as the inversions of the six-membered rings A and C were accounted for during fulfilled conformational analysis. We found that for all these compounds ring C can exist in two stable conformations: “chair” and “boat”. The “chair” conformation is more stable for about ΔE^# (chair → boat) ≈ 2 kcal·mol⁻¹ and the barrier for interconversion between conformations is ΔE^# (chair → boat) ≈ 6 kcal·mol⁻¹. Analogously, ring A can also exist in “chair” and “boat” conformations. The “chair” conformation is more stable for about ΔE^# (chair → boat) ≈ 10 kcal·mol⁻¹ and the barrier for interconversion between conformations is ΔE^# (chair → boat) ≈ 14 kcal·mol⁻¹ (Figure 4 and Figure 5).

To obtain theoretical ECD spectra the excitation energies and the rotatory strengths for 1–4 were calculated using time-dependent density functional theory (TDDFT) with PBE1PBE exchange-correlation functional and cc-pvTz basis set [8]. A comparison of statistically averaged ECD spectra for 1–4 with corresponding experimental spectra is presented in Figure 6. The comparison of all theoretical spectra with the experimental ones showed that all spectra are qualitatively similar in the region λ ≥ 200 nm, where the pronounced Cotton effects occur, thus proving 4R, 5S, 8S, 9R, 10R, 13S absolute configuration for 1; 4R, 5S, 8S, 10R, 13S for 2; 4R, 5S, 8R, 10R, 13S for 3; 4R, 5S, 8S, 10R, 13S for 4.

The molecular formula of 5 was established to be C₁₅H₂₄O₃ from a HRESIMS peak at m/z 283.1538 [M − H]⁻ and by ¹³C NMR analyses. The COSY-45 data and HMBC correlations from H-4 (δ_H 2.11) to C-5 (δ_C 38.5), C-6 (δ_C 29.0), C-10 (δ_C 53.5), from H-5 (δ_H 1.95) to C-6, C-10, from H-6a (δ_H 1.33) to C-4 (δ_C 63.7), C-7 (δ_C 31.8) and C-10, from H-7a (δ_H 1.73) to C-5, C-9 (δ_C 77.2), from H₃-15 (δ_H 1.06) to C-7, C-8 (δ_C 39.2), C-9, from H-9 (δ_H 3.29) to C-5, C-11 (δ_C 67.3), from H-10 (δ_H 1.61) to C-5, C-9, C-11, from H-11 (δ_H 4.38) to C-12 (δ_C 72.7), and from H₃-14 (δ_H 1.36) to C-4, C-12, C-13 (δ_C 77.5) revealed the presence of a decalin moiety in 1 and established the location of methyl groups at C-8 and C-13 and hydroxy groups at C-9, C-11 and C-12. HMBC correlations from H-1a (δ_H 4.22) to C-2 (δ_C 37.9), C-3 (δ_C 206.0) and C-13, from H-2a (δ_H 2.67) to C-1 (δ_C 60.9), C-3, from H-4 (δ_H 2.11) to C-2 and C-3 established a saturated γ-pyrone derivative in 5 (Figure S40). The relative configuration of 5 was assigned based on NOESY cross-peaks (Figure 7) and ¹H-¹H coupling constants (Table 2). Observed NOESY correlations and magnitudes of the vicinal coupling constants between H-4 and H-5; H-5 and H-10; H-9 and H-10; H-10 and H-11; H-11 and H-12 indicated a trans-ring fusion of the A and B rings, cis-ring fusion of the B and C rings, the α-orientation of H₃-14, 9-OH, 11-OH groups and the β-orientation of H₃-15 and 12-OH groups. Compound 5 was named zosteropenilline E.

The molecular formula of 6 was established to be C₁₅H₂₄O₄ from a HRESIMS peak at m/z 291.1579 [M + Na]⁺ and by ¹³C NMR analyses. The ¹³C NMR data of 6 matched those for 1 with the exception of the C-1–C-3 and C-13–C-14 carbon signals. The structure of the decalin moiety and location of the methyl groups at C-8 and C-13 and oxygen functions at C-9 and C-13 were established as for zosteropenilline A (1) based on COSY and HMBC correlations. The COSY-45 data and HMBC correlations from H₂-1 (δ_H 3.91) to C-2 (δ_C 48.6) and C-3 (δ_C 217.6), from H₂-2 (δ_H 2.86, 2.76) to C-1 (δ_C 57.6) and C-3, and from H-4 (δ_H 2.59) to C-3 indicated the presence of a 3-hydroxy-1-oxopropyl residue (C-1–C-3 residue numbering) at C-4. The relative configuration of 6 was assigned on the basis of a NOESY experiment and ¹H-¹H coupling constants (Table 2). Compound 6 was named zosteropenilline F. Zosteropenilline F is an epimer of the pallidopenilline A (13) which was earlier isolated from the P. thomii associated with the brown alga Sargassum pallidum [7]. The ¹H and ¹³C NMR data observed for 6 closely resembled those obtained for pallidopenilline A (measured in CDCl₃) (Figures S58–S68) with the exception of the C-4, C-13 and C-14 carbon and proton signals The molecular formula of 7 was established to be C₁₅H₂₄O₃ from a HRESIMS peak at m/z 275.1621 [M + Na]⁺ and by ¹³C NMR analyses. The ¹³C NMR data (

Table 3. ¹³C NMR spectroscopic data (δ in ppm) for zosteropenillines G–L (7–12).

Position	7 *	8 **	9 *	10 **	11 *	12 **
1	58.1, CH2	57.9, CH2	58.0, CH2	58.0, CH2	57.9, CH2	58.0, CH2
2	49.3, CH2	43.6, CH2	42.1, CH2	49.2, CH2	48.9, CH2	49.5, CH2
3	214.3, C	214.0, C	213.5, C	214.1, C	211.2, C	213.2, C
4	63.5, CH	61.7, CH	59.6, CH	63.4, CH	61.6, CH	57.7, CH
5	41.3, CH	37.9, CH	40.3, CH	41.5, CH	39.4, CH	40.3, CH
6	29.4, CH2	30.5, CH2	29.9, CH2	28.7, CH2	32.4, CH2	32.1, CH2
7	34.8, CH2	31.9, CH2	32.6, CH2	28.9, CH2	27.9, CH2	28.1, CH2
8	32.9, CH	39.2, CH	40.4, CH	40.6, CH	41.1, CH	41.1, CH
9	40.9, CH2	82.3, CH	78.3, CH	35.2, CH2	38.3, CH2	37.2, CH2
10	42.1, CH	49.6, CH	47.2, CH	41.5, CH	166.3, C	144.5, C
11	131.9, CH	73.2, CH	130.6, CH	131.5, CH	120.0, CH	118.8, CH
12	133.7, CH	129.0, CH	129.3, CH	134.0, CH	200.3, C	68.0, CH
13	73.0, C	131.5, C	140.8, C	72.9, C	74.2, C	72.4, C
14	25.9, CH3	20.9, CH3	112.8, CH2	25.9, CH3	21.8, CH3	20.5, CH3
15	22.3, CH3	17.8, CH3	18.4, CH3	68.1, CH2	67.4, CH2	67.8, CH2

* Chemical shifts were measured at 125.77 MHz in CDCl₃; ** Chemical shifts were measured at 176.04 MHz in CDCl₃.

) observed for 7 closely resembled those obtained for zosteropenilline D (4) with the exception of the C-1–C-3 and C-13–C-14 carbon signals. The structure of the decalin moiety, location of the methyl groups at C-8 and C-13, oxygen functions at C-13 and 3-hydroxy-1-oxopropyl residue at C-4 were established by HMBC and COSY correlations (Figures S74 and S75). The relative configuration of 7 was assigned based on NOESY correlations H-4 (δ_H 2.89)/H-10 (δ_H 1.84); H-10/H-8 (δ_H 1.46) and H-5 (δ_H 1.48)/H₃-14 (δ_H 1.20) and H₃-15 (δ_H 0.89) recorded in CDCl₃ and 13-OH (δ_H 4.95)/H-4 correlation in spectrum of 7 recorded in DMSO-d₆ (Figure S77). Compound 7 was named zosteropenilline G.

The molecular formula of 8 was established to be C₁₅H₂₄O₄ from a HRESIMS peak at m/z 291.1571 [M + Na]⁺ and by ¹³C NMR analyses. The ¹H NMR, ¹³C NMR, DEPT and HSQC spectra of 8 (Table 3 and

Table 4. ¹H NMR spectroscopic data (δ, J in Hz) for zosteropenillines G–L (7–12).

Position	7 *	8 **	9 *	10 **	11 *	12 ***
1	a: 3.90, ddd (11.7, 7.1, 3.7) b: 3.86, ddd (11.7, 6.6, 3.7)	3.85, m (2H)	a: 3.91, ddd (11.5, 7.1, 3.9) b: 3.85, ddd (11.5, 6.8, 4.2)	a: 3.91, ddd (11.2, 6.9, 3.6) b: 3.87, ddd (11.2, 6.7, 3.7)	a: 3.96, ddd (11.5, 7.7, 3.7) b: 3.82, ddd (11.5, 6.7, 3.9)	a: 3.95, ddd (11.3, 7.5, 3.5) b: 3.82, ddd (11.3, 6.4, 3.6)
2	a: 3.04, ddd (18.0, 6.8, 3.8) b: 2.60, ddd (18.0, 7.1, 3.8)	a: 2.69, ddd (18.2, 6.6, 4.3) b: 2.64, ddd (18.2, 6.3, 4.3)	a: 2.83, ddd (18.3, 6.8, 3.8) b: 2.65, ddd (18.3, 6.8, 4.0)	a: 3.06, ddd (18.0, 7.1, 3.7) b: 2.61, ddd (18.0, 7.0, 3.7)	a: 3.14, ddd (18.0, 6.5, 3.6) b: 2.66, ddd (18.0, 7.6, 3.9)	a: 3.05, ddd (18.1, 6.5, 3.6) b: 2.69, ddd (18.0, 7.6, 3.7)
4	2.89, d (11.5)	2.92, m	3.15, dtd (12.1, 2.6, 0.9)	2.92, d (11.6)	3.01, d (9.8)	3.09, d (10.0)
5	1.48, m	1.69, m	1.68, m	1.52, dq (11.7, 2.7)	2.89, m	2.55, m
6	a: 1.70, m b: 0.93, m	a: 1.57, dq (13.2, 3.5) b: 1.17, qd (13.1, 3.5)	a: 1.53, m b: 1.14, m	a: 1.79, m b: 0.95, qd (12.3, 3.6)	a: 1.91, dq (12.9, 3.0) b: 1.15, qd (13.1, 3.3)	a: 1.74, m b: 1.12, m
7	a: 1.71, m b: 0.96, m	a: 1.70, m b: 1.03, qd (13.2, 3.5)	a: 1.77, m b: 1.10, m	a: 1.79, m b: 1.02, qd (12.4, 3.6)	a: 1.84, dq (13.1, 3.2) b: 1.29, m	a: 1.79, m b: 1.12, m
8	1.46, m	1.47, m	1.43, m	1.61, m	1.74, m	1.64, m
9	a: 1.73, m b: 0.77, q (12.4)	3.25, t (9.3)	2.89, t (9.9)	a: 1.87, m b: 0.82, q (13.0)	a: 2.60, dq (14.0, 2.5) b: 2.01, m	a: 2.39, dq (13.5, 2.5) b: 1.77, m
10	1.84, m	1.28, dt (11.9, 9.3)	1.85, t (10.0)	1.87, m
11	5.42, brs	4.32, dq (8.9, 2.1)	6.20, brs	5.44, brs	5.90, brs	5.60, dt (5.9, 2.1)
12	5.42, brs	5.53, q (1.8)	6.20, brs	5.44, brs		4.36, dd (5.9, 1.7)
14	1.20, s	1.60, brs	a: 4.99, dd (2.8, 1.3) b: 4.59, dt (2.3, 0.9)	1.20, s	1.19, s	1.20, s
15	0.89, d (6.5)	1.02, d (6.5)	1.05, d (6.5)	a: 3.47, dd (10.6, 6.6) b: 3.45, dd (10.6, 6.6)	a: 3.58, dd (10.5, 5.8) b: 3.54, dd (10.5, 5.8)	a: 3.50, dd (10.5, 5.9) b: 3.48, dd (10.4, 6.2)

* Chemical shifts were measured at 500.13 MHz in CDCl₃; ** Chemical shifts were measured at 700.13 MHz in CDCl₃.

) displayed obvious signals for two methyl (δ_H 1.60, δ_C 20.9 and δ_H 1.02, δ_C 17.8) groups, four methylenes (δ_C 43.6, 30.5, 31.9) including one oxygen-bearing (δ_H 3.85, 2H, δ_C 57.9), seven methines (δ_H 1.69, δ_C 37.9, δ_H 1.47, δ_C 39.2, δ_H 1.28, δ_C 49.6, δ_H 2.92, δ_C 61.7, δ_H 3.25, δ_C 82.3, δ_H 4.32, δ_C 73.2, δ_H 5.53, δ_C 129.0,) including two oxygen-bearing, one carbonyl carbon (δ_C 214.0) and one sp³ quaternary carbon (δ_C 131.5). The structure of a 1,2,3,4-tetrasubstituted cyclohexane ring and side chain in 8 were found by extensive NMR spectroscopy (¹H and ¹³C NMR, COSY, HSQC and HMBC) as for zosteropenillines E (5) and F (6). HMBC correlations from H-4 (δ_H 2.92) to C-5 (δ_C 37.9), C-12 (δ_C 129.0), C-13 (δ_C 131.5), from H-10 (δ_H 1.28) to C-5, C-11 (δ_C 73.2), C-12, from H-11 (δ_H 4.32) to C-12, C-13, and from H₃-14 (δ_H 1.60) to C-4 (δ_C 61.7), C-12, C-13 established a B ring structure, Δ¹² double bond and the location of the hydroxy group at C-11. The relative configuration of 8 was assigned based on NOESY cross-peaks H-4/H-10; H-5 (δ_H 1.69)/H-9 (δ_H 3.25), H-11, H₃-15 (δ_H 1.02); H-8 (δ_H 1.47)/H-10; H-9/H-11 and ¹H-¹H coupling constants (Table 4). Compound 8 was named zosteropenilline H.

The molecular formula of 9 was established to be C₁₅H₂₂O₃ from a HRESIMS peak at m/z 273.1462 [M + Na]⁺ and by ¹³C NMR analyses. Structures of an A ring and side chain in 9 were established as for zosteropenillines E (5) and F (6). Observed long-range COSY correlations H-4 (δ_H 3.15)/H₂-14 (δ_H 4.99, 4.59), H-12 (δ_H 6.20)/H-14b. and HMBC correlations from H-4 (δ_H 3.15) to C-13 (δ_C 140.8), C-14 (δ_C 112.8), from H-9 (δ_H 2.89) and H-10 (δ_H 1.85) to C-11 (δ_C 130.6) and from H₂-14 (δ_H 4.99, 4.59) to C-4 (δ_C 59.6), C-12 (δ_C 129.3), C-13 indicated the presence of a diene system at the C-11 and C-13(14) in 9. The relative configuration of 9 was assigned based on the NOESY correlations H-4/H-10; H-8 (δ_H 1.43)/H-10 and H-5 (δ_H 1.68)/H-9, H₃-15 (δ_H 1.05). Compound 9 was named zosteropenilline I.

The molecular formula of 10 was established to be C₁₅H₂₄O₄ from a HRESIMS peak at m/z 291.1573 [M + Na]⁺ and by ¹³C NMR analyses. The ¹³C NMR data (Table 3) observed for 10 matched the data reported for zosteropenilline G (7) with the exception of the C-7–C-9 and C-15 carbon signals. These data, together with the molecular mass difference of 16 mass units between 7 and 10, indicated the presence of the hydroxymethyl group at C-8 in 10 instead of a methyl group. NOESY cross-peaks H-4 (δ_H 2.92)/H-6b (δ_H 0.95), H-10 (δ_H 1.87); H-5 (δ_H 1.52)/H-7b (δ_H 1.02), H-9b (δ_H 0.82), H₃-14 (δ_H 1.20); H-7b/H-9b, H₂-15 (δ_H 3.47, 3.45); H-8 (δ_H 1.61)/H-6b, H-10 indicated the trans-ring fusion of the A and B rings, a β-orientation of the side chain, H₃-14 and hydroxymethyl group at C-8. Compound 10 was named zosteropenilline J.

The molecular formula of 11 was established to be C₁₅H₂₂O₅ from a HRESIMS peak at m/z 305.1370 [M + Na]⁺ and by ¹³C NMR analyses. The UV spectrum exhibits a λ_max at 242 nm (log ε 3.46), consistent with the enone system in 11. The COSY and HSQC spectra of 11 revealed the partial connectivity sequences of the protons in the A ring as CH(5)-CH₂(6)-CH₂(7)-CH(8) and CH₂(15)-CH(8)-CH₂(9). These data and HMBC correlations from H-9a (δ_H 2.60) to C-7 (δ_C 27.9), C-8 (δ_C 41.1) and C-15 (δ_C 67.4), from H-9b (δ_H 2.01) to C-10 (δ_C 166.3), from H₂-15 (δ_H 3.58, 3.54) to C-7, C-8 and C-9 (δ_C 38.3) established the structure of A ring. Long range correlations from H-4 (δ_H 3.01) to C-5 (δ_C 39.4), C-10, C-12 (δ_C 200.3) and C-13 (δ_C 74.2), from H-11 (δ_H 5.90) to C-5 and C-13 and from H₃-14 (δ_H 1.19) to C-4 (δ_C 61.6), C-12, C-13 determined the structure of B ring and indicated the 10-en-12-one position for the enone chromophore in 11. The structure of side chain in 11 was found by NMR spectroscopy as for zosteropenilline F (6). Observed NOESY correlations H-5 (δ_H 2.89)/H-9b (δ_H 2.01), H₃-14; H₂-15/H-9b indicated these protons to be on the same side of the molecule. These data and the magnitude of the coupling constant of the H-4 signal (δ_H 3.01, J = 9.8 Hz) indicated H-4 and 13-OH to be on the other side of molecule. Compound 11 was named zosteropenilline K.

The molecular formula of 12 was established to be C₁₅H₂₄O₅ from a HRESIMS peak at m/z 307.1501 [M + Na]⁺ and by ¹³C NMR analyses. The structure of the A ring in 12 was established based on COSY and HMBC correlations as for zosteropenilline K (11). HMBC correlations from H-11 (δ_H 5.60) to C-5 (δ_C 40.3), C-9 (δ_C 37.2), C-12 (δ_C 68.0), C-13 (δ_C 72.4), from H-12 (δ_H 4.36) to C-4 (δ_C 57.7), C-10 (δ_C 144.5), C-11 (δ_C 118.8), C-13, and from H₃-14 (δ_H 1.20) to C-4, C-12, C-13 established the structure of B ring, location oxygenated functions at C-12, C-13 and methyl group at C-13 in 12. The relative configuration of 12 was defined based on NOESY correlations H-5/H₃-14; H₃-14/H-12; H-4/H-6b; H-6b/H-8 and the magnitude of the coupling constant of the H-4 signal (δ_H 3.09, J = 10.0 Hz). Compound 12 was named zosteropenilline L. Besides the new zosteropenillines (1–12), a known pallidopenilline A (13) was also isolated from this fungus. For the first time, pallidopenilline A was found in fungus P. thomii KMM 4675 [7].

2.2. Bioassay Results

Compounds 2, 8, and 10 induced a moderate downregulation of NO production in LPS-stimulated macrophages at non-cytotoxic concentration of 10.0 µM. Respectively, NO levels in these cells were decreased by 27.7 ± 1.8, 20.6 ± 1.2, and 22.3 ± 3.8 percent, in comparison with LPS-pretreated control cells. The most effective substance was compound 2, which exhibited the maximal pronounced inhibition of NO formation in lipopolysaccharide-stimulated RAW 264.7 cells (Figure 8).

We have investigated the effect of the isolated zosteropenillines 1–3, 7, 8, 10, and 11 on the viability of human drug-resistant prostate cancer cells PC3 as well as on autophagy in these cancer cells. Induction of autophagy is a well-characterized phenomenon in prostate cancer, frequently associated with cancer cell survival and resistance to therapy [9,10]. Therefore, novel compounds that effectively inhibit prosurvival autophagy are of high interest [10,11]. p62 (or SQSTM) is a cargo protein that targets and binds other proteins to deliver them to autophagosomes for selective autophagy. During autophagy autophagosomes fuse with lysosomes and intra-autophagosomal components are degraded by lysosomal hydrolases. Therefore, an increased level of p62 has previously been associated with inhibition of autophagy flux. In our experiments MTT analysis revealed all compounds to be non-cytotoxic up to 100 µM (data not shown). Consequently, we investigated the effect of the zosteropenillines on the expression of autophagy-related cargo protein p62. Western blotting analysis revealed a slight increase in p62 levels in PC3 cells treated with all the investigated substances (Figure 9), suggesting the drug-induced inhibition of autophagy. The effect on p62 expression was similar to the effect of Bafilomycin A1 (Baf)—a well-established autophagy inhibitor. These results suggest that the investigated compounds are able to inhibit autophagy at non-cytotoxic concentrations and may sensitize human cancer cells to cytotoxic anticancer drugs.

3. Materials and Methods

3.1. General Experimental Procedures

Optical rotations were measured on a Perkin-Elmer 343 polarimeter (Perkin Elmer, Waltham, MA, USA) in MeOH. UV spectra were recorded on a Specord UV VIS spectrometer (Carl Zeiss, Jena, Germany) in MeOH and in n-hexane. IR spectra were determined on a Specord M 82 (Carl Zeiss) in CHCl₃. ECD spectra were measured with a Chirascan-Plus CD Spectrometer (Leatherhead, UK) in MeOH in n-hexane. X-ray crystallographic analysis was carried out on a Bruker Kappa APEX2 diffractometer with graphic-monochromated Mo K_α radiation. ¹H and ¹³C NMR spectra were recorded in CDCl₃ and in DMSO-d₆ on a Bruker Avance-500 (Bruker BioSpin GmbH, Rheinstetten, Germany) and Avance III-700 (Bruker BioSpin GmbH, Rheinstetten, Germany) spectrometers operating at 500.13 MHz and 125.77 MHz and 700.13 and 176.04 MHz, respectively, using TMS as an internal standard. HRESIMS spectra were obtained on an Agilent 6510 Q-TOF LC mass spectrometer (Agilent Technologies, Santa Clara, CA, USA). Low-pressure liquid column chromatography was performed using Si gel L (50/100 μm, Sorbpolimer, Imid, Krasnodar, Russia). Plates (4.5 × 6.0 cm) pre-coated with Si gel (5–17 μm, Sorbfil, Imid, Krasnodar, Russia) were used for thin layer chromatography. Preparative HPLC was carried out on a Shimadzu LC-20 (Shimadzu, USA Manufacturing, Canby, OR, USA) and Agilent 1100 (Agilent Technologies, Ratingen, Germany) chromatographs using an YMC ODS-AM (YMC Co, Ishikawa, Japan) (5 μm, 10 × 250 mm), YMC Si (YMC Co, Ishikawa, Japan) (5 μm, 10 × 250 mm), Supelco Discovery C-18 (Supelco Analytical, Bellefonte, PA, USA) (5 μm, 4.6 × 250 mm), Ultrasphere Si (Beckman Coulter Inc., Brea CA, USA) (5 μm, 4.6 × 250 mm) and Kromasil 3-CelluCoat (Kromasil, Bohus, Sweden) (4.6 × 150 mm) columns and Shimadzu RID-20A (Shimadzu Corporation, Kyoto, Japan) and Agilent 1100 (Agilent Technologies, Ratingen, Germany) refractometers.

3.2. Fungal Strain

The strain of the fungus Penicillium thomii KMM 4674 was isolated from superficial mycobiota of the rhizome sea-grass Zostera marina (Sea of Japan) and was identified on the basis of morphological evaluation.

3.3. Cultivation of P. thomii

The fungus was grown stationary at 22 °C for 21 days in 20 Erlenmeyer flasks (500 mL), each containing 20 g of rice, 20 mg of yeast extract, 10 mg of KH₂PO₄, and 40 mL of natural sea water (Marine Experimental Station of G.B. Elyakov Pacific Institute of Bioorganic Chemistry, Troitsa (Trinity) Bay, Sea of Japan) by Dr. Natalya Kirichuk.

3.4. Extraction and Isolation

At the end of the incubation period, the mycelia and medium were homogenized and extracted with EtOAc (1 L). The obtained extract was concentrated to dryness. The residue (2.46 g) was dissolved in H₂O–EtOH (4:1) (100 mL) and was extracted with n-hexane (0.2 L × 3) and EtOAc (0.2 L × 3). After evaporation of the EtOAc layer, the residual material (2.26 g) was passed over a silica column (3 × 14 cm), which was eluted first with n-hexane (200 mL) followed by a step gradient from 5% to 50% EtOAc in n-hexane (total volume: 5 L). Fractions of 250 mL were collected and combined on the basis of TLC (Si gel, toluene–isopropanol 6:1 and 3:1, v/v).

The n-hexane–EtOAc (75:25) eluate (146 mg) was purified on an YMC ODS-AM column eluting with MeOH–H₂O (80:20) to yield fractions A (15.4 mg), B (10 mg), C (2.3 mg), D (3.3 mg), and individual compound 7 (8.4 mg). Fraction A was purified on a Supelco C-18 eluting with CH₃CN–H₂O (25:75) to yield 3 (2.3 mg). Fraction B was purified on a Kromasil 3-CelluCoat column eluting with CH₃CN–H₂O (25:75) to yield 4 (3.0 mg). Fraction C was purified on an Ultrasphere Si column eluting with EtOAc–n-hexane–EtOH (50:50:5) to yield 9 (1.8 mg). Fraction D was purified on an Ultrasphere Si eluting with EtOAc–n-hexane–EtOH (100:100:5) to yield 5 (0.5 mg). The n-hexane–EtOAc (65:35) eluate (283 mg) was purified on a YMC ODS-AM column eluting with MeOH–H₂O (65:35) to yield 1 (11 mg), 6 (3.0 mg), 8 (6.1 mg), 10 (34.6 mg), 11 (4.6 mg) and 13 (100 mg). The n-hexane–EtOAc (60:40) eluate (200 mg) was purified on a YMC ODS-AM column eluting with MeOH–H₂O (65:35) to yield 2 (83 mg) and on a Supelco C-18 eluting with CH₃CN–H₂O (80:20) to yield 12 (1.6 mg).

3.5. Spectral Data

Zosteropenilline A (1): colorless crystals; ${[\mathsf{\alpha }]}_{\mathrm{D}}^{20}$ −125.0 (c 0.1, MeOH); UV (n-hexane) low intensity band; CD (c 0.05, n-hexane), λ_max (∆ε) 202 (−6.31), 300 (−0.77), 310 (−0.73), 321 (−0.40) nm; IR (CHCl₃) ν_max 3462, 2958, 2928, 1703, 1648, 1601, 1444, 1397, 1120, 1034 cm⁻¹; ¹H and ¹³C NMR data, see Table 1 and Table 2, Supplementary Figures S1–S8; HRESIMS [M + Na]⁺ m/z 273.1461 (calcd. for C₁₅H₂₂O₃Na 273.1461), [M + H]⁺ m/z 251.1636 (calcd. for C₁₅H₂₃O₃ 251.1642).

Zosteropenilline B (2): colorless crystals; ${[\mathsf{\alpha }]}_{\mathrm{D}}^{20}$ −161.6 (c 0.12, MeOH); UV (MeOH low intensity band; CD (c 0.07, MeOH), λmax (∆ε) 201 (−1.55), 291 (−0.23), 332 (+0.03), 365 (−0.03) nm; IR (CHCl₃) ν_max 3460, 2957, 2919, 1701, 1602, 1455, 1385, 1108, 1055 cm⁻¹; ¹H and ¹³C NMR data, see Table 1 and Table 2, Supplementary Figures S11–S19; HRESIMS [M + Na]⁺ m/z 273.1474 (calcd. for C₁₅H₂₂O₃Na 273.1461), [M − H]⁻ m/z 249.1496 (calcd. for C₁₅H₂₁O₃ 249.1496).

Zosteropenilline C (3): white solid; ${[\mathsf{\alpha }]}_{\mathrm{D}}^{20}$ −170.0 (c 0.1, MeOH); UV (MeOH) low intensity band; CD (c 0.07, MeOH), λ_max (∆ε) 204 (−9.86), 297 (−1.63) nm; IR (CHCl₃) ν_max 3604, 2973, 2927, 1705, 1602, 1453, 1375, 1140, 1044 cm⁻¹; ¹H and ¹³C NMR data, see Table 1 and Table 2, Supplementary Figures S20–S27; HRESIMS [M + Na]⁺ m/z 273.1463 (calcd. for C₁₅H₂₂O₃Na 273.1461), [M − H]⁻ m/z 249.1499 (calcd. for C₁₅H₂₁O₃ 249.1496).

Zosteropenilline D (4): amorphous; ${[\mathsf{\alpha }]}_{\mathrm{D}}^{20}$ −56.0 (c 0.06, MeOH); UV (MeOH) low intensity band; CD (c 0.06, MeOH), λ_max (∆ε) 204 (−4.01), 296 (−0.96) nm; IR (CHCl₃) ν_max 2956, 2929, 1706, 1602, 1456, 1376, 1121, 1069 cm⁻¹; ¹H and ¹³C NMR data, see Table 1 and Table 2, Supplementary Figures S28–S35; HRESIMS [M + Na]⁺ m/z 257.1510 (calcd. for C₁₅H₂₂O₂Na 257.1512).

Zosteropenilline E (5): amorphous; ${[\mathsf{\alpha }]}_{\mathrm{D}}^{20}$ −16.0 (c 0.05, MeOH); UV (MeOH) low intensity band; CD (c 0.05, MeOH), λ_max (∆ε) 206 (−0.27), 293 (−0.21), 299 (−0.22), 305 (−0.19), 339 (−0.03); ¹H and ¹³C NMR data, see Table 1 and Table 2, Supplementary Figures S36–S42; HRESIMS [M − H]⁻ m/z 283.1538 (calcd. for C₁₅H₂₃O₅ 283.1551).

Zosteropenilline F (6): white solid; ${[\mathsf{\alpha }]}_{\mathrm{D}}^{20}$ +9.1 (c 0.11, MeOH); UV (MeOH) low intensity band; CD (c 0.07, MeOH), λ_max (∆ε) 194 (+0.70), 204 (−1.14), 230 (−0.12), 293 (+0.08), 319 (−0.02) nm; IR (CHCl₃) ν_max 3621, 2976, 2928, 1702, 1602, 1450, 1390, 1046 cm⁻¹; ¹H and ¹³C NMR data, see Table 1 and Table 2, Supplementary Figures S43–S50; HRESIMS [M + Na]⁺ m/z 291.1579 (calcd. for C₁₅H₂₄O₄Na 291.1567), [2M + Na]⁺ m/z 559.3242 (calcd. for 2C₁₅H₂₄O₄Na 559.3241).

Zosteropenilline G (7): white solid; ${[\mathsf{\alpha }]}_{\mathrm{D}}^{20}$ −15.3 (c 0.034, MeOH); UV (MeOH) λ_max (log ε) low intensity band; CD (c 0.05, MeOH), λ_max (∆ε) 199 (−1.85), 218 (−1.07), 244 (+0.11), 287 (+0.57) nm; IR (CHCl₃) ν_max 3623, 3459, 2884, 1704, 1670, 1602, 1455, 1391, 1056 cm⁻¹; ¹H and ¹³C NMR data, see Table 3 and Table 4, Supplementary Figures S69–S77; HRESIMS [M + Na]⁺ m/z 275.1621 (calcd. for C₁₅H₂₄O₃Na 275.1618), [M − H]⁻ m/z 251.1646 (calcd. for C₁₅H₂₃O₃ 251.1653).

Zosteropenilline H (8): amorphous; ${[\mathsf{\alpha }]}_{\mathrm{D}}^{20}$ +83.4 (c 0.11, MeOH); UV (MeOH) low intensity band; CD (c 0.06, MeOH), λ_max (∆ε) 209 (+3.62), 295 (+1.98) nm; IR (CHCl₃) ν_max 3617, 3489, 2959, 2929, 1703, 1602, 1456, 1383, 1055 cm⁻¹; ¹H and ¹³C NMR data, see Table 3 and Table 4, Supplementary Figures S78–S85; HRESIMS [M + Na]⁺ m/z 291.1571 (calcd. for C₁₅H₂₄O₄Na 291.1567), [2M + Na]⁺ m/z 559.3236 (calcd. for 2C₁₅H₂₄O₄Na 559.3241).

Zosteropenilline I (9): white solid; ${[\mathsf{\alpha }]}_{\mathrm{D}}^{20}$ +80.0 (c 0.07, MeOH); UV (MeOH) low intensity band; CD (c 0.04, MeOH), λ_max (∆ε) 204 (−6.61), 247 (−1.13) nm; ¹H and ¹³C NMR data, see Table 3 and Table 4, Supplementary Figures S86–S93; HRESIMS [M + Na]⁺ m/z 273.1462 (calcd. for C₁₅H₂₂O₃Na 273.1461), [2M + Na]⁺ m/z 523.3029 (calcd. for 2C₁₅H₂₂O₃Na 523.3030).

Zosteropenilline J (10): colorless crystals; ${[\mathsf{\alpha }]}_{\mathrm{D}}^{20}$ −52.9 (c 0.71, MeOH); UV (MeOH) low intensity band; CD (c 0.06, MeOH), λ_max (∆ε) 196 (−3.81), 213 (+0.35), 238 (+0.05), 295 (−2.15) nm; IR (CHCl₃) ν_max 3605, 3497, 2959, 2929, 1702, 1602, 1456, 1383, 1061 cm⁻¹; ¹H and ¹³C NMR data, see Table 3 and Table 4, Supplementary Figures S94–S101; HRESIMS [M + Na]⁺ m/z 291.1573 (calcd. for C₁₅H₂₄O₄Na 291.1567), [2M + Na]⁺ m/z 559.3236 (calcd. for 2C₁₅H₂₄O₄Na 559.3241).

Zosteropenilline K (11): amorphous; ${[\mathsf{\alpha }]}_{\mathrm{D}}^{20}$ +11.1 (c 0.09, MeOH); UV (MeOH) λ_max (log ε) 242 (3.46) nm; CD (c 0.06, MeOH), λ_max (∆ε) 193 (0.75), 219 (−4.62), 244 (+0.65), 258 (−0.13), 279 (0.46), 294 (0.41), 318 (0.35) nm; IR (CHCl₃) ν_max 3617, 3464, 2958, 2927, 1702, 1671, 1653, 1604, 1456, 1390, 1059 cm⁻¹; ¹H and ¹³C NMR data, see Table 3 and Table 4, Supplementary Figures S102–S109; HRESIMS [M + Na]⁺ m/z 305.1370 (calcd. for C₁₅H₂₂O₅Na 305.1359).

Zosteropenilline L (12): amorphous; ${[\mathsf{\alpha }]}_{\mathrm{D}}^{20}$ −54 (c 0.05, MeOH); UV (MeOH) low intensity band; CD (c 0.05, MeOH), λ_max (∆ε) 196 (−1.29), 210 (+0.14), 298 (−1.12), 349 (+0.04) nm; ¹H and ¹³C NMR data, see Table 3 and Table 4, Supplementary Figures S110–S117; HRESIMS [M + Na]⁺ m/z 307.1501 (calcd. for C₁₅H₂₄O₅Na 307.1516).

Pallidopenilline A (13): colorless crystals; ${[\mathsf{\alpha }]}_{\mathrm{D}}^{20}$ −21. (c 0.1, MeOH); UV (MeOH) λ_max (log ε) low intensity band; CD (c 0.1, MeOH), λ_max (∆ε) 196 (−9.89), 213 (+1.14), 294 (−1.78) nm; ¹H and ¹³C NMR data, Supplementary Figures S51–S65; HRESIMS [M + Na]⁺ m/z 291.1575 (calcd. for C₁₅H₂₄O₅Na 291.1567).

3.6. Preparation of (S)-MTPA and (R)-MTPA Esters of 1

To a solution of 1 (1.75 mg) in pyridine were added 4-dimethylaminopyridine (a few crystals) and (R)-MTPA-Cl (1.2 μL) at room temperature, and the mixture was stirred for 1.5 h. After evaporation of the solvent, the residue was purified by HPLC on an YMC Si (5 μm, 10 × 250 mm) column eluted with n-hexane–acetone (85:15) to afford the (S)-MTPA ester of 1 (1a). The (R)-MTPA ester of 1 (1b) was prepared similarly manner using (S)-MTPA-Cl. NMR data of (R, S)-MTPA esters of 1 (Figure S10). HRESIMS (1a) m/z 489.1864 [M + Na]⁺ (calcd. for C₂₅H₂₉F₃O₅Na, 489.1859), m/z 955.3830 [2M + Na]⁺ (calcd for C₅₀H₅₈F₆O₁₀Na, 955.3826); HRESIMS (1b) m/z 489.1858 [M + Na]⁺ (calcd. for C₂₅H₂₉F₃O₅Na, 489.1859), m/z 955.3815 [2M + Na]⁺ (calcd for C₅₀H₅₈F₆O₁₀Na, 955.3826).

3.7. X-ray Crystal Data for 1

Experimental intensity data for C₁₅H₂₂O₃ were collected at T = 296(2) K (α-C₁₅H₂₂O₃) on a BRUKER Kappa APEX2 diffractometer with graphite monochromated Mo K_α radiation (λ = 0.71073 Å). Intensity data were corrected for absorption using the multi-scan method. The structures were solved using direct methods and refined by least-squares calculation in anisotropic approximation for non-hydrogen atoms. Hydrogen atoms were placed at idealized positions and refined using a riding model. Data collection, reduction, and refinement of the lattice parameters were performed using the Apex II software package [12]. All calculations were performed with SHELXL/PC program [13]. Selected bond lengths and hydrogen bonds are listed in the Supplementary Materials, Figure S8. Supplementary crystallographic data (accession numbers CCDC 1522593) can be obtained free of charge from the Cambridge Crystallographic Data Center via http://www.ccdc.cam.ac. uk/data_request/cif (or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, UK; fax: + 44 1223 336 033 or email: [email protected]).

3.8. Quantum Chemical Modeling

The conformational analyses of 1 in a hexane solvent and for 2–4 in a CH₃OH solvent were done using density functional theory (DFT) with the exchange-correlation functional PBE1PBE [14], the polarization continuum model (PCM) [15] and 6-311+G(d) split-valence basis set, implemented in the Gaussian 03 package of programs [16]. The molecular cavity was modeled according to unified force field (radii = UFF). The statistical weights (g_im) of different conformations of 1–4 were obtained according to Equation (1):

$$g_{im}=\frac{e^{-\Delta G_{im}/RT}}{{{\displaystyle \sum }}_i{e}^{-\Delta G_{im}/RT}}$$

(1)

where the summation was done over all possible conformations of 1–4 and ∆G_im = G_i − G_m; G = E_el + G_tr,T + G_rot,T + G_vib,T is a sum of electronic, translational, rotational, and vibrational contributions to the Gibbs free energy, calculated at temperature T = 298.15 K; the subscript “m” denotes conformation, for which G is minimal. The excitation energies and the rotatory strengths were calculated using time-dependent density functional theory (TDDFT). Theoretical ECD spectra (∆ε_calc(λ)) were simulated as a superposition of Gauss-type functions, individual for each transition from electronic ground state to the i-th calculated excited electronic state (1 ≤ i ≤ 50). The same value ξ = 0.20 eV for the bandwidths at 1/e peak heights was used. The total theoretical ECD spectra were obtained after statistical averaging:

$${\epsilon }_{calc}\left(\lambda \right)={\displaystyle \sum }_i{g}_i·\Delta {\epsilon }_{i,calc}\left(\lambda \right)$$

(2)

The scaled theoretical and experimental ECD spectra were obtained according to Equation (3):

$${\epsilon }_{scaled}\left(\lambda \right)=\frac{\Delta \epsilon \left(\lambda \right)}{\left|\Delta \epsilon \left({\lambda }_{peak}\right)\right|}$$

(3)

where the denominator |∆ε(λ_peak)| is a modulo of the peak value for the chosen characteristic band in the corresponding ECD spectrum.

3.9. Measurement of Nitric Oxide Content

RAW 264.7 murine macrophages were plated into 96-well microplates and incubated at 37 °C with 5% CO₂ for 2 h. After adhesion, cells were incubated with tested compounds (10.0 µM) for 24 h. For endogenously generated NO detection studies, the cells were coincubated with 10 µM of FA–OMe fluorescent probe for 8 h [17]. Prior to fluorescence registration, the cells were washed three times with PBS and then bathed in 200 µL/well of PBS. Green fluorescence of cells was registered at λ_ex = 460 nm and λ_em = 524 nm. In each experiment LPS from E. coli serotype 055:B5 (1.0 µg/mL, Sigma-Aldrich, St. Louis, MO, USA) were used as a positive control. Fluorescent intensity was measured using plate reader PHERAstar FS (BMG Labtech GmbH, Ortenberg, Germany).

3.10. Statistical Analysis

All assays were performed at least in triplicate. The results are expressed as the mean ± standard error (SD). A Student’s t-test was used to evaluate the data with the significance level of p < 0.05. The means and standard errors for each treatment were calculated and plotted using SigmaPlot 3.02 software (Jandel Scientific, San Rafael, CA, USA).

3.11. Cell Lines and Culture Conditions

The human prostate cancer cells line PC-3 was purchased from ATCC. Cells were cultured according to the manufacturer’s instructions in 10% FBS/RPMI media (Invitrogen, Paisley, UK) containing penicillin/streptomycin (Invitrogen). Cells were continuously kept in culture for a maximum of three months, and were routinely inspected microscopically for stable phenotype and regularly checked for contamination with mycoplasma. Cell line authentication was recently performed by DSMZ (Braunschweig, Germany) using highly polymorphic short tandem repeat loci [18].

3.12. In Vitro MTT-Based Drug Sensitivity Assay

The in vitro cytotoxicity of individual substances was evaluated using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, which was performed as previously described [19].

3.13. Western Blotting

Western blotting was performed as described before [19]. For detection of the proteins following primary and secondary antibody were used: anti-SQSTM/p62 (#5114, 1:1000, Cell Signaling Technology, Danvers, MA, USA), anti-α-tubulin (T5168, 1:10,000, Sigma-Aldrich, St. Louis, MO, USA), anti-mouse IgG-HRP (NXA931, 1:10,000, GE Healthcare, Little Chalfont, UK), anti-rabbit IgG-HRP (Cell Signaling Technology, Danvers, MA, USA, #7074, 1:5000). Signals were detected using the ECL chemiluminescence system (Thermo Scientific, Rockford, IL, USA) according to the manufacturer’s protocol. Relative optical density of the signal intensity of the bands was quantified with Quantity One 4.6 software (Bio-Rad, Hercules, CA, USA) and normalized first, against corresponding signal of α-tubulin (loading control), and second, against the signal of control sample. Mean values of two independent experiments ± SEM are presented. SEM values were calculated using GraphPad Prism software v. 5.01 (GraphPad Prism software Inc., La Jolla, CA, USA).

4. Conclusions

Zosteropenillines A–L (1–12) belong to the series of lovastatin-related polyketides that are formed by an enzymatic intramolecular Diels–Alder cycloaddition of a linear hexaketide precursor [20,21,22]. Polyketides containing “decalin” moiety exhibit diverse biological properties such as anticancer, antimicrobial, neurotrophic, and growth-stimulating activity [23,24,25,26,27]. Twelve new polyketides, named zosteropenillines A–L (1–12), have been isolated from the extract of the marine-derived fungus Penicillium thomii. The absolute configuration zosteropenilline A (1) was determined by a combination of the modified Mosher’s method, X-ray analysis, and NOESY data. Absolute configurations of zosteropenillines B–D (2–4) were determined by time-dependent density functional theory (TD-DFT) calculations of ECD spectra. Zosteropenillines B, G, and I at a non-toxic concentration of 10.0 µM induced a moderate downregulation of NO production in macrophages stimulated with LPS.