Photopiperazines AâD, Photosensitive Interconverting

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Cite This: J. Nat. Prod. XXXX, XXX, XXX−XXX

Photopiperazines A−D, Photosensitive Interconverting Diketopiperazines with Significant and Selective Activity against U87 Glioblastoma Cells, from a Rare, Marine-Derived Actinomycete of the Family Streptomycetaceae Min Cheol Kim,† Reiko Cullum,† Henrique Machado,† Alexander J. Smith,† Inho Yang,† Jeffrey J. Rodvold,‡ and William Fenical*,†,‡,§ Downloaded via GUILFORD COLG on August 1, 2019 at 14:40:52 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

†

Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093-0204, United States ‡ Moores Comprehensive Cancer Center, University of California, San Diego, La Jolla, California 92093, United States § Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, California 92093-0204, United States S Supporting Information *

ABSTRACT: Photopiperazines A−D (1−4), unsaturated diketopiperazine derivatives, were isolated from the culture broth of a rare, marine-derived actinomycete bacterium, strain AJS-327. This strain shows very poor 16S rRNA sequence similarity to other members of the actinomycete family Streptomycetaceae, indicating it is likely a new lineage within this group. The structures of the photopiperazines were defined by analysis of HR-ESI-TOF-MS spectra in conjunction with the interpretation of 1D and 2D NMR data. The photopiperazines are sensitive to light, causing interconversion among the four olefin geometrical isomers, which made purification of each isomer challenging. The photopiperazines are highly cytotoxic metabolites that show selective toxicity toward U87 glioblastoma and SKOV3 ovarian cancer cell lines.

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(3, 4). It was subsequently discovered that the photopiperazines were photochemically interconverting and that the purification of the minor isomers 3 and 4 could not be fully achieved. Consequently, the structure elucidation of these isomers was undertaken as multicomponent mixtures often highly enhanced in one isomer.

s a continuation of our current interest in the examination of marine microorganisms for the production of agents of potential use in the treatment of cancer,1−3 we examined an unusual actinomycete strain (strain AJS-327) isolated from a sponge fragment sample collected in La Jolla, California. Phylogenetic analysis of this strain showed a weak relationship to the closest related strains within the family Streptomycetaceae (96% similarity to the closest type strain with 1378 bp considered). This weak relationship indicates that strain AJS327 represents a distinct new lineage within the family Streptomycetaceae. Strain AJS-327 was cultivated in a seawater-based medium for 7 days. Ethyl acetate extraction of the whole culture broth led to a rich organic extract that showed significant growth inhibitory activity against four diverse cancer cell lines. LC-MS analysis of active fractions showed a complex of peaks with identical long-wavelength absorptions at 280 and 370 nm. Fractionation of the organic extract led to mixtures rich in photopiperazines A−D (1−4), which were difficult to fully purify. HPLC separation using C-18 RP conditions gave samples of photopiperazines A and B (1, 2) at 70−80% purity, but failed to fully resolve the minor photopiperazines C and D © XXXX American Chemical Society and American Society of Pharmacognosy

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RESULTS AND DISCUSSION

By HPLC analysis the long-wavelength-absorbing photopiperazines eluted between 29 and 32 min. Each peak of the complex showed identical mass spectrometric properties with [M + H]+ m/z values of 296.1393 (Figure 1).4 Subsequently, all three peaks (A−C) were isolated and analyzed by NMR and mass spectrometric methods. Calculations of the relative amounts of each isomer, based upon NMR integration and isolated peak weights, illustrated that the relative concentrations of the photopiperazines were A = 33.5%, B = 39.7%, C = 8.4%, and D = 18.4%. Received: May 6, 2019

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DOI: 10.1021/acs.jnatprod.9b00429 J. Nat. Prod. XXXX, XXX, XXX−XXX

Journal of Natural Products

Article

correlations of H-15 to carbonyl carbon C-11 and to C-12 (δC 125.7), C-17 (δC 22.8), and C-18 (δC 22.8) indicated the diketopiperazine ring was substituted with an indole ring and an isopropyl group at C-8 and C-15, thus suggesting that the origin of this metabolite involved an initial cyclization of tryptophan and leucine. The obvious challenge in assigning the full stereostructure of photopiperazine A (1) was to decipher the configurations of C8, C-9, and C-12, 15 double bonds. To undertake this challenge, it was conceived that the lactam carbonyl functionalities should exert a significant deshielding effect on the C-8 and C-15 proton chemical shifts when these olefins are in Z-configurations. We were pleased to find that a classic natural product, albonoursin,5 had been synthesized, and all four possible olefin isomers were defined using similar reasoning. Synthetic albonoursin analogues with Z olefin geometries showed C-8 and C-12 proton shifts deshielded by ∼0.5 and ∼0.4 ppm by comparison with the E isomers. Similarly, deshielded shifts were observed when the C-15 or C16 protons were in close proximity to the C-11 carbonyl. By comparing data with the synthetic isomers of albonoursin, photopiperazine A (1) was confidently assigned as the 8Z, 12Z isomer. While the photopiperazines are new natural products, a photopiperazine without olefin configuration was reported as a byproduct of a synthesis to prepare 2,5-dioxygenated-4oxides.6 Peak 2 (rt 30.7 min) was also isolated as a pale yellow, amorphous powder. The major component, photopiperazine B (2), composed approximately 70% of the mixture, with photopiperazine D (4) being present at 30%. HRESIMS data for 2 indicated the same molecular formula as 1. Also, the 1H NMR spectroscopic data for 2 were very similar to those of 1 except for the different chemical shifts of some protons (Figures 2 and S13). Analysis of the 2D NMR spectroscopic data indicated that 2 shared the same fundamental composition as 1. The relationship of 1 and 2 could be defined by geometrical differences at C-8, δH 7.06 for 1/δH

Peak 1 (tR 29.6 min), obtained as a pale yellow, amorphous powder, was found to be a mixture of photopiperazines A (1) and C (3) in a 1.0 to 0.2 ratio. The molecular formula of photopiperazine A (1) was assigned as C17H17N3O2 (indicating 11 degrees of unsaturation) based on HRESIMS data coupled with NMR analysis. The 1H NMR spectrum of 1 showed four sequential coupled aromatic proton signals [H-4 (δH 7.66, d, J = 7.9 Hz), H-5 (δH 7.12, t, J = 7.5 Hz), H-6 (δH 7.18, t, J = 7.5 Hz), H-7 (δH 7.43, d, J = 8.1 Hz)], along with a singlet proton H-2 (δH 8.05) assigned as an indole proton (Table 1). This assignment was confirmed by the observation of HMBC correlations from H-2 to C-3a (δC 127.7) and C-7a (δC 136.2). The 1H NMR spectrum of 1 also showed two deshielded protons H-8 (δH 7.06 s) and H-15 (δH 5.68, d, J = 10.4), a methine proton (δH 2.97), and two doublet methyl groups (δH 0.99, d, J = 6.5). In the 13C NMR spectrum two carbonyl carbon signals, C-14 (δC 158.8) and C-11 (δC 158.0), were observed, which when considered with 2D NMR and UV absorption data, indicated that 1 possessed an unsaturated diketopiperazine subunit (Table 1). HMBC correlations from H-8 to the carbonyl carbon C-14 and to C-2 (δC 127.3) and

Figure 1. HPLC profile of the AJS-327 organic extract (Phenomenex Luna 10.0 × 250 mm column using a linear gradient of 30% to 60% MeCN/ H2O over 40 min) detected at 210 nm, illustrating three distinct photopiperazine-containing peaks (containing compounds A−D) between 29 and 32 min and the identical UV spectra obtained from each peak. B



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Table 1. 1H (500 MHz) and 13C (125 MHz) NMR Spectroscopic Data for the Photopiperazines A−D (1−4) in DMSO-d6 1 C#

δC,a type

2 3 3a 4 5 6 7 7a 8 9 11 12 14 15 16 17 18 1-NH 10-NH 13-NH

127.3, CH 108.3, C 127.7, C 118.6, CH 120.5, CH 122.7, CH 112.4, CH 136.2, C 108.5, CH 122.6, C 158.0, C 125.7, C 158.8, C 125.0, CH 24.3, CH 22.8, CH3 22.8, CH3

2

δH, mult (J in Hz) 8.05, s

7.66, 7.12, 7.18, 7.43,

d (7.9) t (7.5) t (7.5) d (8.1)

7.06, s

5.68, d (10.4) 2.97, m 0.99, d (6.5) 0.99, d (6.5) 11.72, s 10.19, s 9.54, s

δC, type 127.1, CH 108.3, C 127.5, C 118.5, CH 120.5, CH 122.6, CH 112.4, CH 136.1, C 107.3, CH 122.6,b C 158.4, C 125.7, C 158.5, C 130.1, CH 25.6, CH 23.4, CH3 23.4, CH3

3

δH, mult (J in Hz)

δC,a type

8.03, s

7.64, 7.10, 7.17, 7.43,

130.3, CH 109.0, C 128.9, C 117.7, CH 120.5, CH 122.4, CH 112.4, CH 136.1, C 113.2, CH 121.9, C 157.6, C 126.5, C 158.8, C 122.9, CH 25.6, CH 23.4, CH3 23.4, CH3

d (7.9) t (7.5) t (7.5) d (8.0)

6.97, s

5.39, d (9.7) 3.69, m 0.98, d (6.7) 0.98, d (6.7) 11.70, s 10.34, s 9.46, s

a

Assignments were made on the basis of HMBC/HSQC experimental data. multiplicity of this signal was not observed due to peak overlapping.

b13

4


7.58, 7.13, 7.16, 7.43,

d (7.5) mc mc mc

6.95, s

5.54, d (10.4) 2.97, m 0.98, d (6.5) 0.98, d (6.5) 11.53, s 10.01, s 10.48, s

δC,a type 130.3, CH 108.9, C 128.9, C 117.6, CH 120.5, CH 122.6, CH 112.4, CH 136.1, C 112.2, CH 121.9, C 157.8, C 126.2, C 158.2, C 128.3, CH 25.5, CH 23.8, CH3 23.8, CH3


7.57, 7.12, 7.16, 7.43,

d (7.7) mc mc mc

6.91, s

5.34, d (9.6) 3.76, mc 0.96, d (6.7) 0.96, d (6.7) 11.50, s 10.19, s 10.39, s

C NMR chemical shift was obtained from 2D HMBC data. cThe

Figure 2. 1H NMR spectrum of photopiperazines A (1, top), B (2, middle), and C (3, bottom). (a, b) The chemical shift differences between the C-15 and C-16 protons when the C-12−C-15 olefin is oriented E rather than Z. Note the minor presence of photopiperazine D (4) as defined by its C-15 doublet protons in (b). (c) Reaction mixture after long-wavelength UV (365 nm) irradiation for 2 h, illustrating significant conversion to 3. Note the significant deshielded effects of the C-2 indole proton, indicating the proximity of this proton to the C-14 carbonyl.

C



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6.97 for 2, and C-15, δH 5.68 for 1/δH 5.39 for 2. This relationship was also supported by differences in proton chemical shifts at H-2 (δH 8.05 for 1 to δH 8.03 for 2) of the indole ring and H-16 (δH 2.97 for 1 to δH 3.69 for 2) of the isopentene substituent. Comparison of these chemical shifts to those for the synthetic albonoursin isomers clearly showed that 2 is the C-8 Z, C-12 E isomer. The structures of photopiperazines C and D (3, 4) were assigned by analysis of the relevant proton and 13C NMR shifts recorded in mixtures. By comparison with the synthetic albonoursin isomers, photopiperazine C was assigned as the C-8 E, C-12 Z isomer, whereas photopiperazine D was assigned as the C-8 E, C-12 E isomer. Photopiperazines C and D were relatively minor components relative to 1 and 2. This can potentially be due to the unfavorable steric interaction of the indole ring and the C-14 carbonyl. Photoisomerization of 1−4. When we purified photopiperazine A (1) as a single HPLC peak (peak 1, Figure 1), an impurity was always observed at a ratio of about 1:0.2 even though we used amber vials and worked under dim light conditions. The same complexity was observed when peak B was isolated, illustrating a small impurity of photopiperazine D (4). Peak 3, when analyzed by NMR, was quite surprisingly found to be a mixture of 1−4. Clearly, clean HPLC peaks are unlikely to be complex mixtures. Consequently, we envisioned that photoisomerization was taking place during isolation and purification. To further explore this concept, photopiperazine A (1) was exposed to long-wavelength UV light (365 nm) for two hours in a Pyrex NMR tube. The ratio of 1 to 3 was inverted from 1:0.2 to 1:1.3, indicating significant conversion of 1 to 3. Subsequent storage of this mixture under room light conditions returned the isomeric mixture to its original composition in a 6 h period (Figures 2 and S1). Amino acid cyclic dimers, commonly called diketopiperazines (DKPs), are a widely distributed class of compounds, very commonly found in microbial extracts.7,8 Although once considered simple breakdown products of protein metabolism, these molecules are now known to possess a wide spectrum of biological activities, which include antitumor and cancer cell cytotoxicity, antimicrobial, antiviral, and immunosuppressive activities, and some are iron-binding siderophores.9 While in the past, DKPs were considered to be ubiquitous and unimportant, it has now been demonstrated that their biosynthesis involves specific biosynthetic pathways, represented by nonribosomal peptide synthetases (NRPSs) and cyclodipeptide synthases (CDPSs).10−13 The closest wellknown naturally occurring analogue to the photopiperazines is albonoursin (5). This compound is known to be produced by a CDPS pathway coupled with a cyclic dipeptide oxidase (CDO), the latter of which produces the unsaturated exocyclic double bonds. The reported biosynthetic gene cluster (BGC) of albonoursin was detected and amplified using the known CDO peptide sequence to yield a 3.8 kb DNA fragment.12 When cloned in the expression host Streptomyces lividans, this cluster led to the production of 5.

Photopiperazine Biosynthetic Gene Cluster. Using the albonoursin BGC as a reference, we carefully examined the sequenced genome for actinomycete strain AJS-327 and have identified an analogous cluster that contains genes (albA, B, and C) that are ca. 53% similar to those found in the albonoursin cluster (Figure 3.).14 Hence it appears that strain AJS-327 has the genetic capacity to produce the photopiperazines by analogous biosynthetic processes. It has been previously reported that the cyclodipeptide synthases confer specificity to the amino acids incorporated and that this is dictated by the amino acids present in two protein pockets, P1 and P2. The cyclodipeptide synthase in AJS-327 is of the NYH family, and while one of the pockets (P1) presents a sequence similarity to previously described tryptophan specificity, the second one (P2) is different from previously identified pockets (see Figures S17 and S18).15,16 Although albonoursin is closely related to the photopiperazines, the literature does not mention the photochemical isomerism we observed for 1−4. Another prominent and related molecule is plinabulin (6, NPI-2358), a semisynthetic unsaturated DKP derived from the fungal metabolite phenylahistin (halimide).17−23 Plinabulin is a highly cytotoxic metabolite targeting tubulin that acts as a vascular-disrupting agent, causing the interruption of tumor blood flow. The drug appears to act by targeting tumor vascular endothelial cells, resulting in tumor necrosis. Plinabulin has a unique target on the tubulin polymer and is being developed for the treatment of cancer. Currently, plinabulin is in worldwide phase III clinical trials for nonsmall-cell lung cancer.23 A number of other exodidehydro-DKPs have also been isolated from microorganisms, and several have been synthesized.24−27 This includes neihumicin from the actinomycete Micromonospora neihuensis25 and several metabolites, XR330, XR334, and 3,6-dibenzylidene-2,5-dioxopiperazine, produced by members of the genus Streptomyces.26,27 Bioactivity of Photopiperazines. The photopiperazines A−D, tested as a mixture of geometrical isomers A (33.5%), B (39.7%), C (8.4%), and D (18.4%), defined as “DKP mixture”, showed potent and selective growth inhibition of human U87 glioblastoma brain cancer and SKOV3 ovarian cancer cell lines with IC50 values of 1.2 × 10−4 μg/mL (4.1 × 10−4 μM) and 2.2 × 10−4 μg/mL (7.5 × 10−4 μM), respectively, after a five-day treatment. The dose−response and selectivity of these agents is further illustrated in Figure 4 by IC50 values of 1.6 μg/mL (5.4 μM) for MDA-MB-231 breast cancer and HCT116 human colon carcinoma, being 12 000-fold less sensitive. It is tempting to speculate that the mechanism of action of the photopiperazines is similar or identical to that of plinabulin, but evidence to demonstrate vascular disruption and tubulin binding is not yet available.

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EXPERIMENTAL SECTION

General Experimental Procedures. UV spectra were measured with a Beckman Coulter DU800 spectrophotometer with a path length of 1 cm, and IR spectra were acquired on a PerkinElmer 1600 FT-IR spectrometer. The 1D and 2D NMR spectroscopic data were obtained on a JEOL 500 MHz NMR spectrometer. Chemical shifts are reported in ppm units (δ), and coupling constants are reported in hertz. NMR chemical shifts were referenced to the residual solvent peaks (δH 2.50 and δC 40.0 for DMSO-d6). High-resolution ESI-TOF mass spectrometric data were recorded on an Agilent 6530 AccurateMass Q-TOF mass spectrometer coupled to an Agilent 1260 LC system with a Phenomenex Luna C18 column (4.6 × 100 mm, 5 μm, flow rate 0.7 mL/min). Preparative HPLC separations were D



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Figure 3. Comparison of the biosynthetic gene cluster observed in the genome of strain AJS-327 with that reported for albonoursin (5). g of yeast, 2 g of peptone, and 1 L of seawater), shaking at 180 rpm for 4 days at 27 °C. After 96 h, the culture medium was used to inoculate 8 × 2.8 L Fernbach flasks each containing 1 L of seawaterbased A1 medium and shaken at 180 rpm at 27 °C. After 7 days of cultivation, the broth was extracted with 16 L of EtOAc, and the solvent was removed under vacuum to yield 1.3 g of organic extract. Isolation of Photopiperazines A−D (1−4). The organic extract (1.3 g) was subjected to silica vacuum flash chromatography, using a step gradient with CH2Cl2 and MeOH (100% CH2Cl2 to 100% MeOH) to afford seven fractions. LC-MS analysis illustrated that the photopiperazines were concentrated in fraction 5. Fraction 5 (850 mg) was then fractionated by C-18 reversed-phase semipreparative HPLC (Phenomenex Luna C-18 column, 250 × 10, 10 μm; 3 mL/ min; 30% to 60% MeCN/H2O over 40 min; UV detection at 210 nm) to yield 1 (mix 3.7 mg, tR 29.6 min) and 2 (mix 4.1 mg, tR 30.7 min). Photopiperazine A (1): (approximately 80% pure) pale yellow, amorphous powder; UV (MeCN) λmax (log ε) 220 (4.24), 2.80 (4.10), 372 (4.27) nm; IR (KBr) νmax 3391, 3175, 2957, 1669, 1458, 1064 cm−1; 1H and 13C NMR data, Table 1; HRESIMS m/z 296.1393 [M + H]+ (calcd for C17H18N3O2, 296.1399). Photopiperazine B (2): (approximately 70% pure) pale yellow, amorphous powder; UV (MeCN) λmax (log ε) 220 (4.23), 280 (4.09) 370 (4.25) nm; IR (KBr) νmax 3395, 3179, 2956, 1673, 1459, 1065 cm−1; 1H and 13C NMR data, Table 1; HRESIMS m/z 296.1395 [M + H]+ (calcd for C17H18N3O2, 296.1399). Photopiperazines C and D (3, 4). These minor analogues were not isolated or purified. They occurred in mixtures with 1 and 2. Their NMR spectroscopic properties, however, were readily extracted from 2D NMR data and are reported in Table 1. Cancer Cell Growth Inhibition Bioassays. Human glioblastoma U87 brain cancer, ovarian cancer SKOV3, breast cancer MDA-MB231, and colorectal carcinoma HCT116 cancer cells were grown in RPMI (Corning) supplemented with 10% fetal bovine serum (HyClone) and 1% penicillin/streptomycin/L-glutamine, nonessential amino acids, sodium pyruvate, and HEPES. For IC50 determination, cells were plated in low density and treated across a titration of specified compound (w/v) in biologic triplicate. After 5 days of treatment, cell abundance was determined by following the AlamarBlue (Thermo) cell viability protocol. Briefly, AlamarBlue was loaded at 1:10 v/v dilution into each well and allowed to be properly metabolized by cells. After incubating for 3−6 h, fluorescence intensity was measured using a Tecan plate reader (excitation: 560 nm, emission: 590 nm). Absorbance values were then normalized to the lowest concentration (1 × 10−5 μg/mL) to determine percent survival. Normalized absorbance values were then plotted and used to calculate IC50 values using nonlinear regression analysis software (Prism). UV Irradiation of Photopiperazines A (1) and B (2). Separate solutions of 1 (2 mg) and 2 (2.5 mg) in DMSO-d6 (200 μL) were prepared and irradiated in 3 mm Pyrex NMR tubes using a model UVGL-25 (UVP Inc., Mineralight lamp, 115 V 60 Hz; 365 nm) for 2 h. The course of the reaction was followed by recording 1H NMR

Figure 4. Growth inhibition response curves (IC50 in μg/mL) for the photopiperazine mixture (1−4) against two sensitive and two far less sensitive cancer cell lines. performed using a Shimadzu SCL-10A with a Shimadzu SPD-10A UV/vis detector and a semipreparative reversed-phase C18 column (Phenomenex Luna, 10.0 × 250 mm, 10 μm) using variable percentages of MeCN in H2O at a flow rate of 3.0 mL/min. Isolation and Phylogenetic Analysis of Strain AJS-327. Strain AJS-327 was isolated from a detached sponge fragment (unidentified) collected in December 2016 on the beach 200 m south of Scripps Institution of Oceanography Pier in La Jolla, CA. The sponge sample was collected in a sterile 50 mL tube and transported to the laboratory within one hour, where it was cut into small fragments with sterile scissors, and fragments were streaked onto A1 medium-based agar plates (10 g of soluble potato starch, 4 g of yeast extract, 2 g of peptone, 750 mL of naturally sourced and filtered seawater that was obtained from the Scripps Institution of Oceanography Pier in La Jolla, 250 mL of distilled H2O, and 18 g of agar). Strain AJS-327 was isolated using the sterile loop method and subcultured using the same agar medium. The strain was identified by partial (1380 bp) 16S rDNA sequence analysis using NCBI BLASTn search (GenBank accession no. MK817028). The closest matching type strains were Streptomyces cacoi strain NBRC 12748 (96% identity; accession number NR_041061.1), Streptomyces oryzae strain NBRC 109761 (96% identity; accession number NR_146025.1), Streptomyces artemisiae strain YIM 63135 (96% identity; accession number NR_116242.1), and Streptomyces armeniacus strain NBRC 12555 (96% identity; accession number NR_112247.1). The poor matches strongly indicate that our strain represents a novel lineage, likely a new genus within the actinomycete family Streptomycetaceae. Cultivation and Extraction. Strain AJS-327 was initially cultured in a 1 L volume using a seawater-based A1 medium (10 g of starch, 4 E



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Pernodet, J. L.; Gondry, M.; Belin, P. Nat. Chem. Biol. 2015, 11, 721− 727. (17) Yamazaki, Y.; Tanaks, K.; Nicholson, B.; Deyanat-Yazdi, G.; Potts, B.; Yoshida, T.; Oda, A.; Kitagawa, T.; Orikasa, S.; Kiso, Y.; Yasui, H.; Akamatsu, M.; Chinen, T.; Usui, T.; Shinozaki, Y.; Yakushiji, F.; Miller, B. R.; Neuteboom, S.; Palladino, M.; Kanoh, K.; Lloyd, G. K.; Hayashi, Y. J. Med. Chem. 2012, 55, 1056−1071. (18) Kanoh, K.; Kohno, S.; Asari, T.; Harada, T.; Katada, J.; Muramatsu, M.; Kawashima, H.; Sekiya, H.; Uno, I. Bioorg. Med. Chem. Lett. 1997, 7, 2847−2852. (19) Singh, A. V.; Bandi, M.; Raje, N.; Richardson, P.; Palladino, M. A.; Chauhan, D.; Anderson, K. C. Blood 2011, 117, 5692−5700 (also see http://drugapprovalsint.com/plinabulin/). (20) Hayashi, Y.; Yamazaki-Nakamura, Y.; Yakushiji, F. Chem. Pharm. Bull. 2013, 61, 889−901. (21) Kanzaki, H.; Yanagisawa, S.; Kanoh, K.; Nitoda, T. J. Antibiot. 2002, 55, 1042−1047. (22) Nicholson, B.; Lloyd, G. K.; Miller, B. R.; Palladino, M. A.; Kiso, Y.; Hayashi, Y.; Neuteboom, S. T. Anti-Cancer Drugs 2006, 17, 25−31. (23) Yamazaki, Y.; Sumikura, M.; Hidaka, K.; Yasui, H.; Kiso, Y.; Yakushiji, F.; Hayashi, Y. Bioorg. Med. Chem. 2010, 18, 3169. (24) Arunrattiyakorn, P.; Ikeda, B.; Nitoda, T.; Kanzaki, H. Biosci., Biotechnol., Biochem. 2007, 71, 830−833. (25) Yang, L.-M.; Wu, R.-Y.; McPhail, A. T.; Yokoi, T.; Lee, K.-H. J. Antibiot. 1988, 41, 488−493. (26) Gerber, N. N. J. Org. Chem. 1967, 32, 4055−4059. (27) Bryans, J.; Charlton, P.; Chicarelli-Robinson, I.; Collins, M.; Faint, R.; Latham, C.; Shaw, I.; Trew, S. J. Antibiot. 1996, 49, 1014.

data. After 2 h, the reaction mixture was returned to room light, and the composition monitored for the next 6 h (see Figure S1).

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jnatprod.9b00429. Additional information (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: (858) 534-2133. ORCID

William Fenical: 0000-0002-8955-1735 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is, in part, the result of financial support from the NIH, National Cancer Institute, under grant R13 CA044848. REFERENCES

(1) Hughes, C. C.; Yang, Y.-L.; Liu, W.-T.; Dorrestein, P. C.; La Clair, J. J.; Fenical, W. J. Am. Chem. Soc. 2009, 131, 12094−12096. (2) Trzoss, L.; Fukuda, T.; Costa-Lotufo, L. V.; Jimenez, P.; La Clair, J. J.; Fenical, W. Proc. Natl. Acad. Sci. U. S. A. 2014, 111, 14687− 14692. (3) Asolkar, R. N.; Singh, A.; Jensen, P. R.; Aalbersberg, W.; Carte, B. K.; Feussner, K.-D.; Subramani, R.; Di Pasquale, A.; Rheingold, A. L.; Fenical, W. Tetrahedron 2017, 73, 2234−2241. (4) The organic extract of this strain is unusually rich in secondary metabolites, containing numerous polyketides, terpenoids, meroterpenoids, nonribosomal peptides, and compounds produced by other biosynthetic pathways. (5) Shin, C.-g.; Hayakawa, M.; Kazutoshi, M.; Yoshimura, J. Tetrahedron Lett. 1977, 10, 863−866. (6) Kita, Y.; Akai, S.; Fujioka, H.; Tamura, Y.; Tone, H.; Taniguchi, Y. J. Chem. Soc., Perkin Trans. 1 1994, 7, 875−884. (7) Borthwick, S. D. Chem. Rev. 2012, 112, 3641−3716. (8) Mishra, A. K.; Choi, J.; Choi, S. J.; Baek, K. H. Molecules 2017, 22, 1796−1809. (9) Cornacchia, C.; Cacciatore, I.; Baldassarre, L.; Mollica, A.; Feliciani, F.; Pinnen, F. Mini-Rev. Med. Chem. 2012, 12, 2−12. (10) Belin, P.; Moutiez, M.; Lautru, S.; Seguin, J.; Pernodet, J. L.; Gondry, M. Nat. Prod. Rep. 2012, 29, 961−979. (11) Gu, B.; He, S.; Yan, X.; Zhang, L. Appl. Microbiol. Biotechnol. 2013, 97, 8439−8453. (12) Lautru, S.; Gondry, M.; Genet, R.; Pernodet, J.-L. Chem. Biol. 2002, 9, 1355−1364. (13) Borgman, P.; Lopez, R. D.; Lane, A. L. Org. Biomol. Chem. 2019, 17, 2305−2314. (14) Genomic DNA derived from actinomycete strain AJS-327 was sequenced by a combination of Pac-Bio and Illumina sequencing. The compiled data indicated a genome size of 6 744 653 bps with 71.68% GC composition. The full genome can be accessed at GenBank, accession no. SKBR00000001. The sequence data were annotated using AntiSMASH to generate numerous putative biosynthetic gene clusters. Full analytical details of the genome will be published elsewhere. (15) Gondry, M.; Jacques, I. B.; Thai, R.; Babin, M.; Canu, N.; Seguin, J.; Belin, P.; Pernodet, J.-L.; Mountez, M. Front. Microbiol. 2018, 9, 6−14. (16) Jacques, I. B.; Moutiez, M.; Witwinowski, J.; Darbon, E.; Martel, C.; Seguin, J.; Favry, E.; Thai, R.; Lecoq, A.; Dubois, S.; F


Photopiperazines AâD, Photosensitive Interconverting

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