Flavonoids and Alkaloids from Marine-Derived Actinomycete Streptomyces sp. C011

Cite this paper: Vietnam J. Chem., 2020, 58(5), 610-614 Article DOI: 10.1002/vjch.202000046 610 Wiley Online Library © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH Flavonoids and Alkaloids from Marine-Derived Actinomycete Streptomyces sp. C011 Tran Thi Thanh Hoa 1,2 , Vu Van Nam 1 , Doan Thi Mai Huong 1,3* , Phi Thi Dao 1 , Nguyen Nam Phuong 4 , Le Thi Hong Minh 1 , Vu Thi Quyen 1 , Nguyen Mai Anh 1 , Brian T. Murphy 5 , Ho Thi Minh Ly 2 , Pham Van Cuong 1,3* 1 Institute of Marine Biochemistry, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay district, Hanoi 10000, Viet Nam 2 National Institute of Hygiene and Epidemiology, 1 Yersin, Hai Ba Trung district, Hanoi 10000, Viet Nam 3 Graduate University of Science and Technology, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay district, Hanoi 10000, Viet Nam 4 Hanoi Amsterdam High School for the gifted, Hoang Minh Giam, Cau Giay district, Hanoi 10000, Viet Nam 5 Department of Pharmaceutical Sciences, College of Pharmacy, University of Illinois at Chicago, 1200 West Harrison St., IL 60607, USA Submitted March 26, 2020; Accepted April 19, 2020 Abstract Five secondary metabolites including three flavonoids, 6-lavandulyl-5,7,2′,4′-tetrahydroxyflavanone (1), 5′- lavandulyl-2′-methoxy-2,4,4′,6′-tetrahydroxychalcone (2), 6-lavandulyl-7-methoxy-5,2′,4′-trihydroxyflavanone (3), and two alkaloids, tryptoline (4), and norharman (5) were isolated from the culture broth of Streptomyces sp. C011. Their structures were determined by spectral data analysis, including MS, 2D NMR, and CD spectrum. All the separated compounds were evaluated for their antimicrobial activities. Compounds 1, 2, 3 and 5 exhibited antimicrobial activity. Keywords. Streptomyces, marine microorganism, actinomycetes, flavonoid, alkaloid. 1. INTRODUCTION Streptomyces comprises over of 500 described species, and belongs to the Streptomycetaceae family. [1-2] The genus Streptomyces is the largest source of bioactive secondary metabolites , such as antitumorals, antivirals, antifungals, immunosuppressants, anti-hypertensives, and antibiotics. [3-5] During our screening program, the ethyl acetate extract of Streptomyces sp. C011 exhibited antimicrobial activity against a gram-positive (E. faecalis ATCC29212, S. aureus ATCC25923, B. cereus ATCC13245) bacteria strain and a fungus strain (C. albicans ATCC10231) with a MIC value of 64, 128, 64, 32 μg/mL, respectively. In this paper, we reported the isolation and structural elucidation of five compound, 6-lavandulyl-5,7,2′,4′- tetrahydroxy flavanone (1), 5′-lavandulyl-2′- methoxy-2,4,4′,6′-tetrahydroxychalcone (2), 6- lavandulyl-7-methoxy-5,2′,4′-trihydroxyflavanone (3), tryptoline (4), and norharman (5) from the extract of the culture broth of Streptomyces sp. C011. Figure 1: Compounds 1-5 isolated from Streptomyces sp. C011 2. MATERIALS AND METHODS 2.1. General Experimental Procedures Optical rotations were recorded on a Polax-2L Vietnam Journal of Chemistry Doan Thi Mai Huong et al. © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 611 polarimeter in MeOH. CD spectra were measured on a Chirascan CD spectrometer. HR-ESI-MS spectra were obtained using an Agilent 6550 iFunnel Q-TOF LC/MS system. The ESI-MS were recorded on an Agilent 1100 LC-MSD Trap spectrometer. All NMR spectra were recorder on a Bruker 500 MHz instrument (Avance 500). TLC silica gel Merck 60 F254 was used as thin-layer chromatography. Column chromatography (CC) was performed on silica-gel (Kieselgel 60) or Sephadex LH-20. 2.2. Marine materials Streptomyces sp. C011 was isolated from a marine crinoid in the sea of Van Phong (Khanh Hoa, Vietnam) in December 2016 and was identified by Prof. Do Cong Thung of Institute of Marine Environment and Resources - Vietnam Academy of Science and Technology (VAST). Voucher specimens were deposited at the Institute of Marine Environment and Resources, Hai Phong, Vietnam. The strain C011 was identified belonging to the genus Streptomyces by using 16S rRNA gene sequence analysis. Strain C011 was cultured in 50 L of high-nutrient medium A1+ (yeast extract: 4 g/L; peptone: 2 g/L; soluble starch: 10 g/L; instant ocean: 30 g/L; CaCO3: 1 g/L; pH 7.0) for 10 days at 28 °C while shaking at 150 rpm. 2.3. Extraction and isolation The culture broth (50 L) of Streptomyces sp. C011 strain was filtered. Then this culture solution was subjected to amberlite-XAD 16 column (Ø 10) and eluted with 40 L of MeOH, combined with concentration under reduced pressure to obtain methanol residue (C011, 172 g). The extract C011 was chromatographed on a Dianion column, eluting with MeOH/H2O (0/100→100/0, v/v) to provide eight fractions, F1-F8. Fraction F2 (17.0 g) was chromatographed on a silica gel column eluting with a gradient of dichloromethane/acetone (100/0→50/50, v/v) to give six sub-fractions, F2.1–F2.6. Sub-fraction F2.2 (0.48 g) was chromatographed on a Sephadex LH-20 column using MeOH to give 5 sub-subfraction, F2.2.1-F2.2.5. Compound 1 (2.5 mg) and 2 (2.1 mg) were obtained from F2.2.2 on a silica gel column eluting with CH2Cl2/EtOAc (100/0→0/100, v/v). Sub-fraction F2.4 (0.6 g) was chromatographed on a Sephadex LH-20 column eluting with MeOH to yield compound 4 (3.2 mg). Fraction F4 (7.0 g) was chromatographed on a silica gel column eluting with CH2Cl2/acetone (100/0→0/100, v/v) to obtain four sub-fractions, F4.1-F4.4. Sub-fraction F4.3 was chromatographed on Sephadex LH-20 column eluting with MeOH to obtain compound 3 (1.7 mg). Fraction F5 (12.0 g) was subjected to CC on silica gel, eluted with CH2Cl2/acetone gradient to obtain five sub-fractions, F5.1-F5.5. The purification of the sub-fraction F5.5 was performed on Sephadex LH-20 column using MeOH, then separated by CC on silica gel eluted with CH2Cl2/acetone (100/0→40/60, v/v) to result compound 5 (3.0 mg). 6-lavandulyl-5,7,2′,4′-tetrahydroxyflavanone (1): Yellow solid, [α]D 27 = +3.1 o (c 0.2, MeOH). CD (MeOH) nm (Δ): 205 (-6.6), 221 (+8.3), 292 (-5.9), 312 (+0.9). HR-ESI-MS: m/z 425.1960 [M+H] + (Calcd. for [C25H29O6] + , 425.1964). 1 H-NMR (CD3OD, 500 MHz) δH (ppm): 1.50 (3H, s, H-6′′), 1.59 (3H, s, H-7′′), 1.65 (3H, s, H-10′′), 2.02 (2H, m, H-3′′), 2.50 (1H, m, H-2′′), 2.60 (2H, m, H-1′′), 2.74 (1H, dd, J = 2.5, 17.0 Hz, Ha-3), 2.98 (1H, dd, J = 13.5, 17.0 Hz, Hb-3), 4.54 (1H, d, J = 2.0 Hz, Ha-9′′), 4.60 (1H, m, Hb-9′′), 4.99 (1H, m, H-4′′), 5.57 (1H, dd, J = 3.0, 13.5 Hz, H-2), 5.91 (1H, s, H-8), 6.36 (1H, dd, J = 2.0, 8.0 Hz, H-5′), 6.38 (1H, d, J = 2.5 Hz, H-3′), 7.32 (1H, d, J = 8.0 Hz, H-6´). 13C-NMR (CD3OD, 125 MHz) δC (ppm): 17.83 (C-6′′), 19.22 (C-10′′), 25.84 (C-7′′), 28.0 (C-1′′), 32.33 (C-3′′), 43.30 (C-3), 48.48 (C-2′′), 75.76 (C-2), 96.40 (C-8), 103.18 (C-10), 103.41 (C-3′), 107.68 (C-5′), 108.73 (C-6), 111.14 (C-9′′), 118.39 (C-1′), 124.84 (C-4′′), 128.61 (C-6′), 132.0 (C-5′′), 149.78 (C-8′′), 156.67 (C-2′), 159.57 (C-4´), 162.61 (C-5), 163.22 (C-9), 167.01 (C-7), 198.85 (C-4). 5′-lavandulyl-2′-methoxy-2,4,4′,6′- tetrahydroxychalcone (2): Yellow solid, [α]27D = -1.9 (c 0.5, CH2Cl2), HR-ESI-MS: m/z 439.2117 [M+H] + (Calcd. for [C26H31O6] + , 439.2121). 1 H- NMR (CD3OD, 500 MHz) δH (ppm): 1.57 (3H, s, H- 6′′), 1.64 (3H, s, H-7′′), 1.72 (3H, s, H-10′′), 2.09 (2H, m, H-3′′), 2.55 (1H, m, H-2′′), 2.63 (2H, d, J = 8.0 Hz, H-1′′), 3.89 (3H, s, OCH3), 4.57 (1H, d, J = 2.5 Hz, Ha-9′′), 4.61 (1H, m, Hb-9′′), 5.06 (1H, t, J = 6.5 Hz, H-4′′), 5.97 (1H, s, H-3′), 6.31 (1H, m, H-5), 6.33 (1H, d, J = 2.0 Hz, H-3), 7.39 (1H, d, J = 8.5 Hz, H-6), 7.94 (1H, d, J = 15.5 Hz, H-α), 8.02 (1H, d, J = 15.5 Hz, H-β). 13C-NMR (CD3OD, 125 MHz) δC (ppm): 17.88 (C-6′′), 19.05 (C-10′′), 25.91 (C- 7′′), 28.15 (C-1′′), 32.43 (C-3′′), 48.01 (C-2′′), 56.05 (OCH3), 91.59 (C-3′), 103.67 (C-3), 106.51 (C-1′), 108.85 (C-5′), 108.96 (C-5), 111.13 (C-9′′), 116.25 (C-1), 125.04 (C-4′′), 125.42 (C-α), 131.56 (C-6), 131.77 (C-5′′), 139.77 (C-β), 149.86 (C-8′′), 160.31 (C-2), 162.26 (C-4), 162.43 (C-4′), 164.08 (C-2′), 166.63 (C-6′), 194.75 (C-γ). 6-lavandulyl-7-methoxy-5,2′,4′- trihydroxyflavanone (3): White solid, [α]D 27 = -28.3 (c 0.8, MeOH). HR-ESI-MS: m/z 439.2115 [M+H] + Vietnam Journal of Chemistry Flavonoids and alkaloids from © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 612 (Calcd. for [C26H31O6] + , 439,2121). 1 H-NMR (CD3OD, 500 MHz) δH (ppm): 1.49 (3H, s, H-12), 1.58 (3H, s, H-13), 1.65 (3H, s, H-16), 2.04 (2H, m, H-9), 2.51 (1H, m, H-8), 2.63 (1H, d, J = 5.5 Hz, Ha- 7), 2.65 (1H, d, J = 5.5 Hz, Hb-7), 3.82 (3H, s, -OCH3), 4.54 (1H, d, J = 2.5 Hz, Ha-15), 4.59 (1H, dd, J = 1.5, 2.5 Hz, Hb-15), 4.98 (1H, t, J = 7.0 Hz, H-10), 6.11 (1H, s, H-5), 6.35 (1H, d, m, H-3′), 6.37 (1H, m, H-5′), 7.32 (1H, d, J = 8.5 Hz, H-6′). 13C- NMR (CD3OD, 125 MHz) δC (ppm): 17.82 (C-6′′), 19.18 (C-10′′), 25.85 (C-7′′), 28.19 (C-1′′), 32.37 (C- 3′′), 48.20 (C-3, C-2′′), 55.92 (-OCH3), 75.46 (C-2), 93.35 (C-8), 103.39 (C-3′), 105.74 (C-10), 107.64 (C-5′), 109.57 (C-6), 111.15 (C-9′′), 118.48 (C-1′), 124.81 (C-4′′), 128.48 (C-6′), 132.02 (C-5′′), 149.78 (C-8′′), 156.64 (C-2′), 159.46 (C-4′), 161.86 (C-7), 164.86 (C-5), 164.86 (C-9), 193.89 (C=O). Tryptoline (4): White solid, mp. 204-205 o C. ESI-MS: m/z 173 [M+H] + . 1 H-NMR (CD3OD) δH (ppm): 2.78 (2H, t, J = 5.5 Hz, H-4), 3.15 (2H, t, J = 5.5 Hz, H-3), 6.96 (1H, ddd, J = 1.0, 8.0, 9.0 Hz, H- 6), 3.99 (2H, s, H-1), 7.05 (1H, ddd, J = 1.5, 7.5, 9.0 Hz, H-7), 7.27 (1H, dd, J = 1.0, 8.0 Hz, H-8), 7.40 (1H, d, J = 7.5 Hz, H-5). 13 C-NMR (125 MHz, CD3OD) δC (ppm): 22.72 (C-4), 43.51 (C-1), 44.59 (C-3), 108.28 (C-4a), 111.71 (C-5), 118.33 (C-8), 119.58 (C-6), 121.86 (C-7), 128.74 (C-4b), 133.31 (C-9a), 137.66 (C-8a). Norharman (5): White solid, mp. 198-200 o C; ESI-MS: m/z 169 [M+H] + . 1 H-NMR (500 MHz, CD3OD) δH (ppm): 7.29 (1H, dd, J = 2.5, 8.0 Hz, H- 6), 7.58 (1H, dd, J = 0.5, 8.5 Hz, H-7), 7.59 (1H, d, J = 8.5 Hz, H-8), 8.11 (1H, d, J = 5.5 Hz, H-4), 8.21 (1H, d, J = 8.0 Hz, H-5), 8.31 (1H, d, J = 5.5 Hz, H- 3), 8.81 (1H, s, H-1). 13 C-NMR (125 MHz, CD3OD) δC (ppm): 112.84 (C-8), 116.08 (C-4), 120.85 (C-6), 122.22 (C-4b), 122.72 (C-5), 129.75 (C-7), 130.46 (C-4a), 134.11 (C-1), 137.80 (C-9a), 138.42 (C-3), 142.77 (C-8a). 3. RESULTS AND DISCUSSION Compound 1 was obtained yellow amorphous solid, and was optically active [α]D 27 = +3.1 o (c 0.2, MeOH). Its molecular formula was determined as C25H28O6 by HR-ESI-MS at m/z 425.1960 [M+H] + (Calcd. for [C25H29O6] + , 425.1964). The 13 C-NMR, DEPT and HSQC spectra of 1 showed the signals of 25 carbons, including three methyl groups at δC 17.83 (C-6′′), 19.22 (C-10′′), 25.84 (C-7′′), one carbonyl group at δC 198.85 (C-4), four methylene groups, two sp 3 methine groups, five sp 2 methine groups, and ten quaternary carbons. The 1H-NMR spectrum of 1 showed the signal of one aromatic proton of A ring at δH 5.91 (1H, s, H-8), three ABX aromatic protons of B ring at δH 6.36 (1H, dd, J = 2.0, 8.0 Hz H-5′), 6.38 (1H, d, J = 2.5 Hz, H-3′), 7.32 (1H, d, J = 8.0 Hz, H-6´), three protons of C ring at δH 5.57 (1H, dd, J = 3.0, 13.5 Hz, H-2), 2.74 (1H, dd, J = 2.5, 17.0 Hz, Ha-3), 2.98 (1H, dd, J = 13.5, 17.0 Hz, Hb-3) suggested the presence of flavanone moiety. In addition, the signal of three methyl groups at δH 1.50 (3H, s, H-6′′), 1.59 (3H, s, H-7′′), 1.65 (3H, s, H-10′′), one sp2 methylene group at δH 4.54 (1H, d, J = 2.0 Hz, Ha-9′′), 4.60 (1H, m, Hb-9′′), one olefinic proton at δH 4.99 (1H, m, H-4′′), and a number aliphatic protons from 2.02 to 2.98 ppm were also noted. The 1 H- 1 H COSY data revealed three spin-spin coupling systems: CH2- 1′′/H-2′′/CH2-3′′/H-4′′, H-5′/H-6′, and H-2/CH2-3 (figure 2). In the HMBC spectrum, cross-peaks of H-2′′ with C-8′′, C-9′′, C-10′′, C-4′′, C-6; H-4′′ with C-6′′, C-7′′; and those of H-1′′ with C-3′′, C-2′′, C-8′′ indicated the lavandulyl group in the structure of 1. Futhermore, HMBC corelation of the proton of CH2- 1′′ with C-5, C-6 and C-7 indicated the linkage of the lavandulyl group at C-6 (figure 2). A negative Cotton effect at 292 nm (Δ -5.9), and a positive Cotton effect at 312 nm (Δ +0.9) were observed in the CD spectrum of 1 revealing the S-configuration for carbon C-2. [6-8] Consequently, the structure of 1 was elucidated as 6-lavandulyl-5,7,2′,4′- tetrahydroxyflavanone. [8-9] Compound 2 was obtained as an optically active [α]27D = -1.9 (c 0.5, CH2Cl2). The HR-ESI-MS data exhibited a quasi-molecular ion [M+H] + at m/z 439.2117 (Calcd. for [C26H31O6] + , 439.2121). Along with the 13 C-NMR data, a molecular formula of C26H30O6 was suggested for 2. Comparison of the 1 H-NMR and 13 C-NMR spectra with those of 1 revealed the same substructures, lavandulyl group, A ring and B ring systems for compound 2. However, the CH=CH system [δH 7.94 (1H, d, J = 15.5 Hz, H- α), δC 125.42 (C-α); δH 8.02 (1H, d, J = 15.5 Hz, H- β), δC 139.77 (C-β)] were observed in the 1D-NMR of 2 instead of the resonances of the coupling system CH-2/CH2-3 in the structure of 1. Three spin-spin coupling systems of 2 were established from their 1 H- 1 H COSY spectrum analysis such as CH2-1′′/H- 2′′/CH2-3′′/H-4′′, H-α/H-β, and H-5/H-6. The connection of these systems was established by HMBC correlations (figure 2). The HMBC correlations between H-β and C-6 (δC 109.57)/C-2 (δC 160.31)/C-γ (δC 194.75) determined the linkage of the C-β with C-1 of A ring. HMBC correlations from H-1′′ to C-4′, C-5′ and C-6′, suggested the position of lavandulyl group at C-5′. Additionally, the positions of the methoxy group at C-2′ were defined by HMBC correlations of methoxy protons Vietnam Journal of Chemistry Doan Thi Mai Huong et al. © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 613 with C-2′. Thus, complete analyses of the 2D-NMR spectra and comparison with the reported data allowed determining the structure of 2 to be 5′- lavandulyl-2′-methoxy-2,4,4′,6′- tetrahydroxychalcone. [7-9] Figure 2: The key HMBC and COSY correlations of compounds 1 and 2 Compound 3 was obtained as an optically active [α]D 27 = -28.3 (c 0.8, MeOH). The molecular formula of 3 was deduced to be C26H30O6 based on its HR- ESI-MS at m/z: 439.2115 [M+H] + (Calcd. for [C26H31O6] + , 439.2121). The 1D-NMR of compound 3 showed the signals similar of compound 1, except for the presence of a methoxy group (δH 3.82, δC 55.92) in 3. Analyses of the NMR spectra, [α]D, and comparison with previously reported literature, [8-9] compound 3 was identified as 6-lavandulyl-7- methoxy-5,2′,4′-trihydroxyflavanone. Compound 4 was obtained as white solid, mp. 204-205 o C. The ESI-MS spectrum of 4 showed the pseudomolecular ion peak at m/z 173 [M+H] + . Considering the 13 C-NMR data, a molecular formula of C11H12N2 was suggested for 4. In the 1 H-NMR spectrum, the presence of an 1,2-disubstituted benzene ring [δH 7.40 (1H, d, J = 7.5 Hz, H-5), 7.27 (1H, dd, J = 1.0, 8.0 Hz, H-8), 7.05 (1H, ddd, J = 1.5, 7.5, 9.0 Hz, H-7), 6.96 (1H, ddd, J = 1.0, 8.0, 9.0 Hz, H-6)], and the signals of proton at δH from 2.78 to 3.99 were noted. The 13 C-NMR and DEPT spectra of 4 showed signals of 11 carbons, including four methine sp 2 groups, three methylene sp 3 groups and four quaternary carbons. The ESI-MS, NMR data of 4 was in agreement with that reported for tryptoline. [10] Compound 5 was isolated as white solid, mp. 198-200 o C. ESI-MS showed the proton adduct ion [M+H] + at m/z 169. The 13 C-NMR spectra of 5 showed signals of 11 cacbon, including seven sp 2 methine groups and four quaternary carbons. The carbon chemical shift of C-1 (δC 134.11), C-9a (δC 137.80), C-3 (δC 138.42), C-8a (δC 142.77) suggested their linkage to nitrogen. The 1 H-NMR spectrum showed the signals of an 1,2-disubstituted benzene ring at δH 7.29 (1H, dd, J = 2.5, 8.0 Hz, H- 6), 7.58 (1H, dd, J = 0.5, 8.5 Hz, H-7), 7.59 (1H, d, J = 8.5 Hz, H-8), 8.21 (1H, d, J = 8.0 Hz, H-5), and three aromatic protons at δH 8.11 (1H, d, J = 5.5 Hz, H-4), 8.31 (1H, d, J = 5.5 Hz, H-3), 8.81 (1H, s, H-1). Intensive analysis of the 2D-NMR spectra defined the structure of 5 as norharman. Its NMR data were consistent with those reported in the literature. [11] All the separated compounds (1-5) were evaluated for their antibacterial activity against three Gram-positive bacteria (Enterococcus faecalis, Staphylococcus aureus, and Bacillus cereus), three Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa and Salmonella enterica), and antiyeast property against Candida albicans. Compound 1 exhibited antimicrobial activity against E. faecalis and S. aureus, B. cereus, P. aeruginosa, S. enterica and C. albicans with MIC values of 1 to 8 µg/mL. Compound 2 showed inhibitory activity against Gram-positive, Gram-negative and C. albicans with MIC values of 4 to 16 µg/mL. Compound 3 showed inhibitory activity for all test streams with MIC values of 16 to 128 µg/mL. Compound 5 was selectively inhibited S. aureus with MIC value of 32 µg/mL while compound 4 provided a MIC value greater than 256 µg/mL (table 1). Table 1: Antibacterial and antifungal activities of compounds 1-5 (MIC: μg/mL) Compounds Gram-positive Gram-negative Yeast E. faecalis S. aureus B. cereus E. coli P. aeruginosa S. enterica C. albicans 1 1 1 1 >256 1 8 1 2 8 8 8 4 8 8 16 3 32 32 16 128 32 32 32 4 >256 >256 >256 >256 >256 >256 >256 5 >256 32 >256 >256 >256 >256 >256 Streptomycin 256 256 128 32 256 128 - Cyclohexamide - - - - - - 32 Vietnam Journal of Chemistry Flavonoids and alkaloids from © 2020 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 614 4. CONCLUSION Five secondary metabolites including three flavonoids, 6-lavandulyl-5,7,2′,4′-tetrahydroxy flavanone (1), 5′-lavandulyl-2′-methoxy-2,4,4′,6′- tetrahydroxychalcone (2), 6-lavandulyl-7-methoxy- 5,2′,4′-trihydroxyflavanone (3), and two alkaloids, tryptoline (4), and norharman (5) were isolated from the culture broth of Streptomyces sp. C011. Their chemical structures were determined by means of spectroscopic methods including 1D, 2D-NMR, MS and CD data. Acknowledgements. We thank to Prof. Do Cong Thung, Institute of Marine Environment and Resources for marine sample collection. This research was funded by the Fogarty International Center of the National Institutes of Health under Award Number D43TW010530. REFERENCES 1. V. S. Bernan, M. Greenstein, W. M. Maiese. Marine microorganisms as a source of new natural products, Adv. Appl. Microbiol., 1997, 43, 57-90. 2. A. Hasani, A. Kariminik, K. Issazadeh. Streptomycetes: Characteristics and Their Antimicrobial Activities, Int. J. 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